The SQL Server DELETE Query is used to delete the existing records from a table.

You have to use WHERE clause with DELETE query to delete selected rows, otherwise all the records would be deleted.

Syntax

Following is the basic syntax of DELETE query with WHERE clause −

DELETE FROM table_name
WHERE [condition];

You can combine N number of conditions using AND or OR operators.

Example

Consider the CUSTOMERS table having the following records −

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Following command is an example, which would DELETE a customer, whose ID is 6 −

DELETE FROM CUSTOMERS
WHERE ID = 6;

CUSTOMERS table will now have the following records.

ID  NAME       AGE       ADDRESS              SALARY
1   Ramesh     32        Ahmedabad            2000.00
2   Khilan     25        Delhi                1500.00
3   kaushik    23        Kota                 2000.00
4   Chaitali   25        Mumbai               6500.00
5   Hardik     27        Bhopal               8500.00
7   Muffy      24        Indore               10000.00

If you want to DELETE all the records from CUSTOMERS table, you do not need to use WHERE clause. DELETE query would be as follows −

DELETE FROM CUSTOMERS;

CUSTOMERS table now will not have any record.

T-SQL – Overview

In 1970”s the product called ”SEQUEL”, structured English query language, developed by IBM and later SEQUEL was renamed to ”SQL” which stands for Structured Query Language.

In 1986, SQL was approved by ANSI (American national Standards Institute) and in 1987, it was approved by ISO (International Standards Organization).

SQL is a structure query language which is a common database language for all RDBMS products. Different RDBMS product vendors have developed their own database language by extending SQL for their own RDBMS products.

T-SQL stands for Transact Structure Query Language which is a Microsoft product and is an extension of SQL Language.

Example

MS SQL Server – SQLT-SQL

ORACLE – SQLPL-SQL

T-SQL – Data Types

SQL Server data type is an attribute that specifies types of data of any object. Each column, variable and expression has related data type in SQL Server. These data types can be used while creating tables. You can choose a particular data type for a table column based on your requirement.

SQL Server offers seven categories including other category of data types for use.

Exact Numeric Types

Numeric and decimal are Fixed precision and scale data types and are functionally equivalent.

Approximate Numeric Types

Date and Time Types

Character Strings

Unicode Character Strings

Binary Strings

Other Data Types

• sql_variant − Stores values of various SQL Server-supported data types, except text, ntext, and timestamp.

• timestamp − Stores a database-wide unique number that gets updated every time a row gets updated.

• uniqueidentifier − Stores a globally unique identifier (GUID).

• xml − Stores XML data. You can store XML instances in a column or a variable (Introduced in SQL Server 2005).

• cursor − A reference to a cursor.

• table − Stores a result set for later processing.

• hierarchyid − A variable length, system data type used to represent position in a hierarchy (Introduced in SQL Server 2008).

T-SQL – Create Tables

Creating a basic table involves naming the table and defining its columns and each column”s data type.

The SQL Server CREATE TABLE statement is used to create a new table.

Syntax

Following is the basic syntax of CREATE TABLE statement −

CREATE TABLE table_name(
   column1 datatype,
   column2 datatype,
   column3 datatype,
   .....
   columnN datatype,
   PRIMARY KEY( one or more columns ));

CREATE TABLE is the keyword telling the database system what you want to do. In this case, you want to create a new table. The unique name or identifier for the table follows the CREATE TABLE statement. Then in brackets comes the list defining each column in the table and what sort of data type it is. The syntax becomes clearer to understand with the following example.

A copy of an existing table can be created using a combination of the CREATE TABLE statement and the SELECT statement. You can check complete details at Create Table Using another Table.

Example

In this example, let’s create a CUSTOMERS table with ID as primary key and NOT NULL are the constraints showing that these fields cannot be NULL while creating records in this table −

CREATE TABLE CUSTOMERS(
   ID   INT              NOT NULL,
   NAME VARCHAR (20)     NOT NULL,
   AGE  INT              NOT NULL,
   ADDRESS  CHAR (25) ,
   SALARY   DECIMAL (18, 2),
   PRIMARY KEY (ID));

You can verify if your table has been created successfully by looking at the message displayed by the SQL server, otherwise you can use the following command −

exec sp_columns CUSTOMERS

The above command produces the following output.

TABLE_QUALIFIER   TABLE_OWNER   TABLE_NAME   COLUMN_NAME   DATA_TYPE   TYPE_NAME
   PRECISION   LENGTH SCALE   RADIX   NULLABLE   REMARKS   COLUMN_DEF   SQL_DATA_TYPE
   SQL_DATETIME_SUB   CHAR_OCTET_LENGTH   ORDINAL_POSITION   IS_NULLABLE   SS_DATA_TYPE

TestDB    dbo    CUSTOMERS   ID        4    int      10   4    0      10     0
   NULL   NULL   4   NULL    NULL      1    NO       56

TestDB    dbo    CUSTOMERS   NAME      12   varchar  20   20   NULL   NULL   0
   NULL   NULL   12   NULL   20        2    NO       39

TestDB    dbo    CUSTOMERS   AGE       4    int      10   4    0      10     0
   NULL   NULL   4   NULL    NULL      3    NO       56

TestDB    dbo    CUSTOMERS   ADDRESS   1    char     25   25   NULL   NULL   1
   NULL   NULL   1   NULL    25   4    YES  39

TestDB    dbo    CUSTOMERS   SALARY    3    decimal  18   20   2      10     1
   NULL   NULL   3   NULL    NULL      5    YES      106

You can now see that CUSTOMERS table is available in your database which you can use to store required information related to customers.

T-SQL – Drop Tables

The SQL Server DROP TABLE statement is used to remove a table definition and all data, indexes, triggers, constraints, and permission specifications for that table.

Note − You have to be careful while using this command because once a table is deleted then all the information available in the table would also be lost forever.

Syntax

Following is the basic syntax of DROP TABLE statement −

DROP TABLE table_name;

Example

Let us first verify CUSTOMERS table and then we will delete it from the database −

Exec sp_columns CUSTOMERS;

The above command shows the following table.

TABLE_QUALIFIER   TABLE_OWNER   TABLE_NAME   COLUMN_NAME   DATA_TYPE   TYPE_NAME
   PRECISION   LENGTH SCALE   RADIX   NULLABLE   REMARKS   COLUMN_DEF   SQL_DATA_TYPE
   SQL_DATETIME_SUB   CHAR_OCTET_LENGTH   ORDINAL_POSITION   IS_NULLABLE   SS_DATA_TYPE

TestDB    dbo    CUSTOMERS   ID        4   int        10   4    0      10     0
   NULL   NULL   4   NULL    NULL      1   NO         56

TestDB    dbo    CUSTOMERS   NAME      12  varchar    20   20   NULL   NULL   0
   NULL   NULL   12   NULL   20        2   NO         39

TestDB    dbo    CUSTOMERS   AGE       4   int        10   4    0      10     0
   NULL   NULL   4   NULL    NULL      3   NO         56

TestDB    dbo    CUSTOMERS   ADDRESS   1   char       25   25   NULL   NULL   1
   NULL   NULL   1   NULL    25        4   YES        39

TestDB    dbo    CUSTOMERS   SALARY   3   decimal     18   20   2      10     1
   NULL   NULL   3   NULL    NULL     5   YES         106

CUSTOMERS table is available in the database, so let us drop it. Following is the command for the same.

DROP TABLE CUSTOMERS;
Command(s) completed successfully.

With the above command, you will not get any rows.

Exec sp_columns CUSTOMERS;
No rowsdata will be displayed

T-SQL – INSERT Statement

The SQL Server INSERT INTO statement is used to add new rows of data to a table in the database.

Syntax

Following are the two basic syntaxes of INSERT INTO statement.

INSERT INTO TABLE_NAME [(column1, column2, column3,...columnN)]
VALUES (value1, value2, value3,...valueN);

Where column1, column2,…columnN are the names of the columns in the table into which you want to insert data.

You need not specify the column(s) name in the SQL query if you are adding values for all the columns of the table. But make sure the order of the values is in the same order as the columns in the table. Following is the SQL INSERT INTO syntax −

INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN);

Example

Following statements will create six records in CUSTOMERS table −

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, ''Ramesh'', 32, ''Ahmedabad'', 2000.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, ''Khilan'', 25, ''Delhi'', 1500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (3, ''kaushik'', 23, ''Kota'', 2000.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (4, ''Chaitali'', 25, ''Mumbai'', 6500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (5, ''Hardik'', 27, ''Bhopal'', 8500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (6, ''Komal'', 22, ''MP'', 4500.00 );

Syntax

You can create a record in CUSTOMERS table using second syntax as follows −

INSERT INTO CUSTOMERS VALUES (7, ''Muffy'', 24, ''Indore'', 10000.00 );

All the above statements will produce the following records in CUSTOMERS table −

ID  NAME       AGE         ADDRESS              SALARY
1   Ramesh     32          Ahmedabad            2000.00
2   Khilan     25          Delhi                1500.00
3   kaushik    23          Kota                 2000.00
4   Chaitali   25          Mumbai               6500.00
5   Hardik     27          Bhopal               8500.00
6   Komal      22          MP                   4500.00
7   Muffy      24          Indore               10000.00

Populate One Table Using Another Table

You can populate data into a table through SELECT statement over another table provided another table has a set of fields, which are required to populate first table. Following is the syntax −

INSERT INTO first_table_name
   SELECT column1, column2, ...columnN
      FROM second_table_name
      [WHERE condition];

T-SQL – SELECT Statement

SQL Server SELECT statement is used to fetch the data from a database table which returns data in the form of result table. These result tables are called result-sets.

Syntax

Following is the basic syntax of SELECT statement −

SELECT column1, column2, columnN FROM table_name;

Where, column1, column2…are the fields of a table whose values you want to fetch. If you want to fetch all the fields available in the field, then you can use the following syntax −

SELECT * FROM table_name;

Example

Consider the CUSTOMERS table having the following records −

ID  NAME       AGE       ADDRESS             SALARY
1   Ramesh     32        Ahmedabad           2000.00
2   Khilan     25        Delhi               1500.00
3   kaushik    23        Kota                2000.00
4   Chaitali   25        Mumbai              6500.00
5   Hardik     27        Bhopal              8500.00
6   Komal      22        MP                  4500.00
7   Muffy      24        Indore              10000.00

Following command is an example, which would fetch ID, Name and Salary fields of the customers available in CUSTOMERS table −

SELECT ID, NAME, SALARY FROM CUSTOMERS;

The above command will produce the following output.

ID  NAME          SALARY
1   Ramesh        2000.00
2   Khilan        1500.00
3   kaushik       2000.00
4   Chaitali      6500.00
5   Hardik        8500.00
6   Komal         4500.00
7   Muffy         10000.00

If you want to fetch all the fields of CUSTOMERS table, then use the following query −

SELECT * FROM CUSTOMERS;

The above will produce the following output.

ID  NAME       AGE       ADDRESS              SALARY
1   Ramesh     32        Ahmedabad            2000.00
2   Khilan     25        Delhi                1500.00
3   kaushik    23        Kota                 2000.00
4   Chaitali   25        Mumbai               6500.00
5   Hardik     27        Bhopal               8500.00
6   Komal      22        MP                   4500.00
7   Muffy      24        Indore               10000.00

T-SQL – UPDATE Statement

The SQL Server UPDATE Query is used to modify the existing records in a table.

You can use WHERE clause with UPDATE query to update selected rows otherwise all the rows would be affected.

Syntax

Following is the basic syntax of UPDATE query with WHERE clause −

UPDATE table_name
SET column1 = value1, column2 = value2...., columnN = valueN
WHERE [condition];

You can combine N number of conditions using AND or OR operators.

Example

Consider the CUSTOMERS table having the following records −

ID  NAME       AGE       ADDRESS             SALARY
1   Ramesh     32        Ahmedabad           2000.00
2   Khilan     25        Delhi               1500.00
3   kaushik    23        Kota                2000.00
4   Chaitali   25        Mumbai              6500.00
5   Hardik     27        Bhopal              8500.00
6   Komal      22        MP                  4500.00
7   Muffy      24        Indore              10000.00

Following command is an example, which would update ADDRESS for a customer whose ID is 6 −

UPDATE CUSTOMERS
SET ADDRESS = ''Pune''
WHERE ID = 6;

CUSTOMERS table will now have the following records −

ID  NAME       AGE       ADDRESS             SALARY
1   Ramesh     32        Ahmedabad           2000.00
2   Khilan     25        Delhi               1500.00
3   kaushik    23        Kota                2000.00
4   Chaitali   25        Mumbai              6500.00
5   Hardik     27        Bhopal              8500.00
6   Komal      22        Pune                4500.00
7   Muffy      24        Indore              10000.00

If you want to modify all ADDRESS and SALARY column values in CUSTOMERS table, you do not need to use WHERE clause. UPDATE query would be as follows −

UPDATE CUSTOMERS
SET ADDRESS = ''Pune'', SALARY = 1000.00;

CUSTOMERS table will now have the following records.

ID  NAME       AGE       ADDRESS          SALARY
1   Ramesh     32        Pune             1000.00
2   Khilan     25        Pune             1000.00
3   kaushik    23        Pune             1000.00
4   Chaitali   25        Pune             1000.00
5   Hardik     27        Pune             1000.00
6   Komal      22        Pune             1000.00
7   Muffy      24        Pune             1000.00

T-SQL – DELETE Statement

The SQL Server DELETE Query is used to delete the existing records from a table.

You have to use WHERE clause with DELETE query to delete selected rows, otherwise all the records would be deleted.

Syntax

Following is the basic syntax of DELETE query with WHERE clause −

DELETE FROM table_name
WHERE [condition];

You can combine N number of conditions using AND or OR operators.

Example

Consider the CUSTOMERS table having the following records −

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Following command is an example, which would DELETE a customer, whose ID is 6 −

DELETE FROM CUSTOMERS
WHERE ID = 6;

CUSTOMERS table will now have the following records.

ID  NAME       AGE       ADDRESS              SALARY
1   Ramesh     32        Ahmedabad            2000.00
2   Khilan     25        Delhi                1500.00
3   kaushik    23        Kota                 2000.00
4   Chaitali   25        Mumbai               6500.00
5   Hardik     27        Bhopal               8500.00
7   Muffy      24        Indore               10000.00

If you want to DELETE all the records from CUSTOMERS table, you do not need to use WHERE clause. DELETE query would be as follows −

DELETE FROM CUSTOMERS;

CUSTOMERS table now will not have any record.

T-SQL – WHERE Clause

The MS SQL Server WHERE clause is used to specify a condition while fetching the data from single table or joining with multiple tables.

If the given condition is satisfied, only then it returns a specific value from the table. You will have to use WHERE clause to filter the records and fetch only necessary records.

The WHERE clause is not only used in SELECT statement, but it is also used in UPDATE, DELETE statement, etc., which we would examine in subsequent chapters.

Syntax

Following is the basic syntax of SELECT statement with WHERE clause −

SELECT column1, column2, columnN
FROM table_name
WHERE [condition]

You can specify a condition using comparison or logical operators like >, <, =, LIKE, NOT, etc. The following example will make this concept clear.

Example

Consider the CUSTOMERS table having the following records −

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Following command is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000.

SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE SALARY > 2000;

The above command will produce the following output.

ID  NAME       SALARY
4   Chaitali   6500.00
5   Hardik     8500.00
6   Komal      4500.00
7   Muffy      10000.00

Following command is an example, which would fetch ID, Name and Salary fields from the CUSTOMERS table for a customer with the name ‘Hardik’. It is important to note that all the strings should be given inside single quotes (””) whereas numeric values should be given without any quote as in the above example −

SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE NAME = ''Hardik

The above command will produce the following output.

ID  NAME     SALARY
5   Hardik   8500.00

T-SQL – LIKE Clause

The MS SQL Server LIKE clause is used to compare a value to similar values using wildcard operators. There are two wildcards used in conjunction with the LIKE operator −

• The percent sign (%)
• The underscore (_)

The percent sign represents zero, one, or multiple characters. The underscore represents a single number or character. The symbols can be used in combinations.

Syntax

Following is the basic syntax of % and _.

SELECT *column-list FROM table_name
WHERE column LIKE ''XXXX%''

or

SELECT *column-list FROM table_name
WHERE column LIKE ''%XXXX%''

or

SELECT *column-list FROM table_name
WHERE column LIKE ''XXXX_''

or

SELECT *column-list FROM table_name
WHERE column LIKE ''_XXXX''

or

SELECT  *column-list FROM table_name
WHERE column LIKE ''_XXXX_''

You can combine N number of conditions using AND or OR operators. XXXX could be any numeric or string value.

Example

Following are a number of examples showing WHERE part having different LIKE clause with ”%” and ”_” operators.

Consider the CUSTOMERS table having the following records.

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Following command is an example, which will display all the records from CUSTOMERS table where SALARY starts with 200.

SELECT * FROM CUSTOMERS
WHERE SALARY LIKE ''200%

The above command will produce the following output.

ID   NAME     AGE     ADDRESS       SALARY
1    Ramesh   32      Ahmedabad     2000.00
3    kaushik  23      Kota          2000.00

T-SQL – ORDER BY Clause

The MS SQL Server ORDER BY clause is used to sort the data in ascending or descending order, based on one or more columns. Some database sort query results in ascending order by default.

Syntax

Following is the basic syntax of ORDER BY clause.

SELECT column-list
FROM table_name
[WHERE condition]
[ORDER BY column1, column2, .. columnN] [ASC | DESC];

You can use more than one column in the ORDER BY clause. Make sure whatever column you are using to sort, that column should be in column-list.

Example

Consider the CUSTOMERS table having the following records −

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Following command is an example, which would sort the result in ascending order by NAME and SALARY.

SELECT * FROM CUSTOMERS
   ORDER BY NAME, SALARY

The above command will produce the following output.

ID  NAME       AGE       ADDRESS           SALARY
4   Chaitali   25        Mumbai            6500.00
5   Hardik     27        Bhopal            8500.00
3   kaushik    23        Kota              2000.00
2   Khilan     25        Delhi             1500.00
6   Komal      22        MP                4500.00
7   Muffy      24        Indore            10000.00
1   Ramesh     32        Ahmedabad         2000.00

Following command is an example, which would sort the result in descending order by NAME.

SELECT * FROM CUSTOMERS
   ORDER BY NAME DESC

The above command will produce the following result −

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
7   Muffy      24        Indore             10000.00
6   Komal      22        MP                 4500.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
5   Hardik     27        Bhopal             8500.00
4   Chaitali   25        Mumbai             6500.00

T-SQL – GROUP BY Clause

The SQL Server GROUP BY clause is used in collaboration with the SELECT statement to arrange identical data into groups.

The GROUP BY clause follows the WHERE clause in a SELECT statement and precedes the ORDER BY clause.

Syntax

Following is the basic syntax of GROUP BY clause. The GROUP BY clause must follow the conditions in the WHERE clause and must precede the ORDER BY clause if one is used.

SELECT column1, column2
FROM table_name
WHERE [ conditions ]
GROUP BY column1, column2
ORDER BY column1, column2

Example

Consider the CUSTOMERS table is having the following records −

ID  NAME       AGE       ADDRESS          SALARY
1   Ramesh     32        Ahmedabad        2000.00
2   Khilan     25        Delhi            1500.00
3   kaushik    23        Kota             2000.00
4   Chaitali   25        Mumbai           6500.00
5   Hardik     27        Bhopal           8500.00
6   Komal      22        MP               4500.00
7   Muffy      24        Indore           10000.00

If you want to know the total amount of salary on each customer, then following will be the GROUP BY query.

SELECT NAME, SUM(SALARY) as [sum of salary] FROM CUSTOMERS
   GROUP BY NAME;

The above command will produce the following output.

NAME        sum of salary
Chaitali    6500.00
Hardik      8500.00
kaushik     2000.00
Khilan      1500.00
Komal       4500.00
Muffy       10000.00
Ramesh      2000.00

Let us now consider the following CUSTOMERS table having the following records with duplicate names.

ID  NAME       AGE       ADDRESS           SALARY
1   Ramesh     32        Ahmedabad         2000.00
2   Khilan     25        Delhi             1500.00
3   kaushik    23        Kota              2000.00
4   Chaitali   25        Mumbai            6500.00
5   Hardik     27        Bhopal            8500.00
6   Komal      22        MP                4500.00
7   Muffy      24        Indore            10000.00

If we want to know the total amount of salary on each customer, then following will be GROUP BY query.

SELECT NAME, SUM(SALARY) as [sum of salary] FROM CUSTOMERS
   GROUP BY NAME

The above command will produce the following output.

NAME        sum of salary
Hardik      8500.00
kaushik     8500.00
Komal       4500.00
Muffy       10000.00
Ramesh      3500.00

T-SQL – DISTINCT Clause

The MS SQL Server DISTINCT keyword is used in conjunction with SELECT statement to eliminate all the duplicate records and fetching only unique records.

There may be a situation when you have multiple duplicate records in a table. While fetching such records, it makes more sense to fetch only unique records instead of fetching duplicate records.

Syntax

Following is the basic syntax of DISTINCT keyword to eliminate duplicate records.

SELECT DISTINCT column1, column2,.....columnN
FROM table_name
WHERE [condition]

Example

Consider the CUSTOMERS table having the following records.

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Let us see how the following SELECT query returns duplicate salary records.

SELECT SALARY FROM CUSTOMERS
   ORDER BY SALARY

The above command will produce the following output where salary 2000 comes twice which is a duplicate record from the original table.

SALARY
1500.00
2000.00
2000.00
4500.00
6500.00
8500.00
10000.00

Let us now use DISTINCT keyword with the above SELECT query and see the result.

SELECT DISTINCT SALARY FROM CUSTOMERS
   ORDER BY SALARY

The above command produces the following output where we do not have any duplicate entry.

SALARY
1500.00
2000.00
4500.00
6500.00
8500.00
10000.00

T-SQL – Joining Tables

The MS SQL Server Joins clause is used to combine records from two or more tables in a database. A JOIN is a means for combining fields from two tables by using values common to each.

Consider the following two tables, (a) CUSTOMERS table is as follows −

ID  NAME       AGE       ADDRESS             SALARY
1   Ramesh     32        Ahmedabad           2000.00
2   Khilan     25        Delhi               1500.00
3   kaushik    23        Kota                2000.00
4   Chaitali   25        Mumbai              6500.00
5   Hardik     27        Bhopal              8500.00
6   Komal      22        MP                  4500.00
7   Muffy      24        Indore              10000.00

(b) Another table is ORDERS as follows −

OID  DATE                       CUSTOMER_ID        AMOUNT
100  2009-10-08 00:00:00.000    3                  1500.00
101  2009-11-20 00:00:00.000    2                  1560.00
102  2009-10-08 00:00:00.000    3                  3000.00
103  2008-05-20 00:00:00.000    4                  2060.00

Let us join these two tables in our SELECT statement as follows −

SELECT ID, NAME, AGE, AMOUNT
   FROM CUSTOMERS, ORDERS
   WHERE  CUSTOMERS.ID = ORDERS.CUSTOMER_ID
OR
SELECT A.ID, A.NAME, A.AGE, B.AMOUNT
   FROM CUSTOMERS A inner join  ORDERS B on A.ID = B.Customer_ID

The above command will produce the following output.

ID   NAME      AGE    AMOUNT
2    Khilan    25     1560.00
3    kaushik   23     1500.00
3    kaushik   23     3000.00
4    Chaitali  25     2060.00

It is noticeable that the join is performed in the WHERE clause. Several operators can be used to join tables, such as =, <, >, <>, <=, >=, !=, BETWEEN, LIKE, and NOT; they can all be used to join tables. However, the most common operator is the equal symbol.

MS SQL Server Join Types −

There are different types of joins available in MS SQL Server −

• INNER JOIN − Returns rows when there is a match in both tables.

• LEFT JOIN − Returns all rows from the left table, even if there are no matches in the right table.

• RIGHT JOIN − Returns all rows from the right table, even if there are no matches in the left table.

• FULL JOIN − Returns rows when there is a match in one of the tables.

• SELF JOIN − This is used to join a table to itself as if the table were two tables, temporarily renaming at least one table in the MS SQL Server statement.

• CARTESIAN JOIN − Returns the Cartesian product of the sets of records from the two or more joined tables.

T-SQL – Sub-Queries

A sub-query or Inner query or Nested query is a query within another SQL Server query and embedded within the WHERE clause. A sub query is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved.

Sub queries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN, etc.

There are a few rules that sub queries must follow −

• You must enclose a subquery in parenthesis.

• A subquery must include a SELECT clause and a FROM clause.

• A subquery can include optional WHERE, GROUP BY, and HAVING clauses.

• A subquery cannot include COMPUTE or FOR BROWSE clauses.

• You can include an ORDER BY clause only when a TOP clause is included.

• You can nest sub queries up to 32 levels.

Subqueries with SELECT Statement

Syntax

Subqueries are most frequently used with the SELECT statement. Following is the basic syntax.

SELECT column_name [, column_name ]
FROM   table1 [, table2 ]
WHERE  column_name OPERATOR
   (SELECT column_name [, column_name ]
   FROM table1 [, table2 ]
   [WHERE])

Example

Consider the CUSTOMERS table having the following records.

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Let us apply the following subquery with SELECT statement.

SELECT *
   FROM CUSTOMERS
   WHERE ID IN (SELECT ID FROM CUSTOMERS WHERE SALARY > 4500)

The above command will produce the following output.

ID  NAME       AGE       ADDRESS          SALARY
4   Chaitali   25        Mumbai           6500.00
5   Hardik     27        Bhopal           8500.00
7   Muffy      24        Indore           10000.00

Subqueries with INSERT Statement

Sub queries also can be used with INSERT statements. The INSERT statement uses the data returned from the subquery to insert into another table. The selected data in the subquery can be modified with any of the character, date, or number functions.

Syntax

Following is the basic syntax.

INSERT INTO table_name [ (column1 [, column2 ]) ]
   SELECT [ *|column1 [, column2 ]
   FROM table1 [, table2 ]
   [ WHERE VALUE OPERATOR ]

Example

Consider a table CUSTOMERS_BKP with similar structure as CUSTOMERS table. Following is the syntax to copy complete CUSTOMERS table into CUSTOMERS_BKP.

INSERT INTO CUSTOMERS_BKP
   SELECT * FROM CUSTOMERS
   WHERE ID IN (SELECT ID FROM CUSTOMERS)

Subqueries with UPDATE Statement

The subquery can be used in conjunction with the UPDATE statement. Either single or multiple columns in a table can be updated when using a subquery with the UPDATE statement.

Syntax

Following is the basic syntax.

UPDATE table
SET column_name = new_value
[ WHERE OPERATOR [ VALUE ]
   (SELECT COLUMN_NAME
   FROM TABLE_NAME)
   [ WHERE) ]

Example

Let us assume we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table.

Following command example updates SALARY by 0.25 times in CUSTOMERS table for all the customers whose AGE is greater than or equal to 27.

UPDATE CUSTOMERS
   SET SALARY = SALARY * 0.25
   WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP WHERE AGE >= 27 )

This will impact two rows and finally CUSTOMERS table will have the following records.

ID  NAME       AGE       ADDRESS             SALARY
1   Ramesh     32        Ahmedabad           500.00
2   Khilan     25        Delhi               1500.00
3   kaushik    23        Kota                2000.00
4   Chaitali   25        Mumbai              6500.00
5   Hardik     27        Bhopal              2125.00
6   Komal      22        MP                  4500.00
7   Muffy      24        Indore              10000.00

Subqueries with DELETE Statement

The subquery can be used in conjunction with the DELETE statement like with any other statements mentioned above.

Syntax

Following is the basic syntax.

DELETE FROM TABLE_NAME
[ WHERE OPERATOR [ VALUE ]
   (SELECT COLUMN_NAME
   FROM TABLE_NAME)
   [ WHERE) ]

Example

Let us assume we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table.

Following command example deletes records from CUSTOMERS table for all the customers whose AGE is greater than or equal to 27.

DELETE FROM CUSTOMERS
   WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP WHERE AGE >=27 )

This would impact two rows and finally CUSTOMERS table will have the following records.

ID  NAME       AGE       ADDRESS          SALARY
2   Khilan     25        Delhi            1500.00
3   kaushik    23        Kota             2000.00
4   Chaitali   25        Mumbai           6500.00
6   Komal      22        MP               4500.00
7   Muffy      24        Indore           10000.00

T-SQL – Stored Procedures

The MS SQL Server Stored procedure is used to save time to write code again and again by storing the same in database and also get the required output by passing parameters.

Syntax

Following is the basic syntax of Stored procedure creation.

Create procedure <procedure_Name>
As
Begin
<SQL Statement>
End
Go

Example

Consider the CUSTOMERS table having the following records.

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Following command is an example which would fetch all records from the CUSTOMERS table in Testdb database.

CREATE PROCEDURE SelectCustomerstabledata
AS
SELECT * FROM Testdb.Customers
GO

The above command will produce the following output.

ID  NAME       AGE       ADDRESS           SALARY
1   Ramesh     32        Ahmedabad         2000.00
2   Khilan     25        Delhi             1500.00
3   kaushik    23        Kota              2000.00
4   Chaitali   25        Mumbai            6500.00
5   Hardik     27        Bhopal            8500.00
6   Komal      22        MP                4500.00
7   Muffy      24        Indore            10000.00

T-SQL – Transactions

A transaction is a unit of work that is performed against a database. Transactions are units or sequences of work accomplished in a logical order, whether in a manual fashion by a user or automatically by some sort of a database program.

A transaction is the propagation of one or more changes to the database. For example, if you are creating a record or updating a record or deleting a record from the table, then you are performing a transaction on the table. It is important to control transactions to ensure data integrity and to handle database errors.

Practically, you will club many SQL queries into a group and you will execute all of them together as a part of a transaction.

Properties of Transactions

Transactions have the following four standard properties, usually referred to by the acronym ACID −

• Atomicity − Ensures that all operations within the work unit are completed successfully; otherwise, the transaction is aborted at the point of failure, and previous operations are rolled back to their former state.

• Consistency − Ensures that the database properly changes state upon a successfully committed transaction.

• Isolation − Enables transactions to operate independently of and transparent to each other.

• Durability − Ensures that the result or effect of a committed transaction persists in case of a system failure.

Transaction Control

There are following commands used to control transactions −

• COMMIT − To save the changes.

• ROLLBACK − To roll back the changes.

• SAVEPOINT − Creates points within groups of transactions in which to ROLLBACK.

• SET TRANSACTION − Places a name on a transaction.

Transactional control commands are only used with the DML commands INSERT, UPDATE and DELETE only. They cannot be used while creating tables or dropping them because these operations are automatically committed in the database.

In order to use transactional control commands in MS SQL Server, we have to begin transaction with ‘begin tran’ or begin transaction command otherwise these commands will not work.

COMMIT Command

The COMMIT command is the transactional command used to save changes invoked by a transaction to the database. This command saves all transactions to the database since the last COMMIT or ROLLBACK command.

Syntax

Following is the syntax for COMMIT command.

COMMIT;

Example

Consider the CUSTOMERS table having the following records.

ID  NAME       AGE       ADDRESS           SALARY
1   Ramesh     32        Ahmedabad         2000.00
2   Khilan     25        Delhi             1500.00
3   kaushik    23        Kota              2000.00
4   Chaitali   25        Mumbai            6500.00
5   Hardik     27        Bhopal            8500.00
6   Komal      22        MP                4500.00
7   Muffy      24        Indore            10000.00

Following command example will delete records from the table having age = 25 and then COMMIT the changes in the database.

Begin Tran
DELETE FROM CUSTOMERS
   WHERE AGE = 25
COMMIT

As a result, two rows from the table would be deleted and SELECT statement will produce the following output.

ID  NAME       AGE       ADDRESS           SALARY
1   Ramesh     32        Ahmedabad         2000.00
3   kaushik    23        Kota              2000.00
5   Hardik     27        Bhopal            8500.00
6   Komal      22        MP                4500.00
7   Muffy      24        Indore            10000.00

ROLLBACK Command

The ROLLBACK command is the transactional command used to undo transactions that have not already been saved to the database. This command can only be used to undo transactions since the last COMMIT or ROLLBACK command was issued.

Syntax

Following is the syntax for ROLLBACK command.

ROLLBACK

Example

Consider the CUSTOMERS table having the following records.

ID  NAME       AGE       ADDRESS            SALARY
1   Ramesh     32        Ahmedabad          2000.00
2   Khilan     25        Delhi              1500.00
3   kaushik    23        Kota               2000.00
4   Chaitali   25        Mumbai             6500.00
5   Hardik     27        Bhopal             8500.00
6   Komal      22        MP                 4500.00
7   Muffy      24        Indore             10000.00

Following command example will delete records from the table having age = 25 and then ROLLBACK the changes in the database.

Begin Tran
DELETE FROM CUSTOMERS
   WHERE AGE = 25;
ROLLBACK

As a result, delete operation will not impact the table and SELECT statement will produce the following result.

ID  NAME       AGE       ADDRESS          SALARY
1   Ramesh     32        Ahmedabad        2000.00
2   Khilan     25        Delhi            1500.00
3   kaushik    23        Kota             2000.00
4   Chaitali   25        Mumbai           6500.00
5   Hardik     27        Bhopal           8500.00
6   Komal      22        MP               4500.00
7   Muffy      24        Indore           10000.00

SAVEPOINT Command

SAVEPOINT is a point in a transaction when you can roll the transaction back to a certain point without rolling back the entire transaction.

Syntax

Following is the syntax for SAVEPOINT command.

SAVE TRANSACTION SAVEPOINT_NAME

This command serves only in the creation of a SAVEPOINT among transactional statements. The ROLLBACK command is used to undo a group of transactions.

Following is the syntax for rolling back to a SAVEPOINT.

ROLLBACK TO SAVEPOINT_NAME

In the following example, we will delete three different records from the CUSTOMERS table. We will have to create a SAVEPOINT before each delete, so that we can ROLLBACK to any SAVEPOINT at any time to return the appropriate data to its original state.

Example

Consider the CUSTOMERS table having the following records −

ID  NAME       AGE       ADDRESS          SALARY
1   Ramesh     32        Ahmedabad        2000.00
2   Khilan     25        Delhi            1500.00
3   kaushik    23        Kota             2000.00
4   Chaitali   25        Mumbai           6500.00
5   Hardik     27        Bhopal           8500.00
6   Komal      22        MP               4500.00
7   Muffy      24        Indore           10000.00

Following are the series of operations −

Begin Tran
SAVE Transaction SP1
Savepoint created.
DELETE FROM CUSTOMERS WHERE ID = 1
1 row deleted.
SAVE Transaction SP2
Savepoint created.
DELETE FROM CUSTOMERS WHERE ID = 2
1 row deleted.
SAVE Transaction SP3
Savepoint created.
DELETE FROM CUSTOMERS WHERE ID = 3
1 row deleted.

The three deletions have taken place, however, we have changed our mind and decide to ROLLBACK to the SAVEPOINT that we identified as SP2. Because SP2 was created after the first deletion, the last two deletions are undone −

ROLLBACK Transaction SP2
Rollback complete.

Notice that only the first deletion took place since we rolled back to SP2.

SELECT * FROM CUSTOMERS

6 rows selected.

ID  NAME       AGE       ADDRESS          SALARY
2   Khilan     25        Delhi        1500.00
3   kaushik    23        Kota             2000.00
4   Chaitali   25        Mumbai           6500.00
5   Hardik     27        Bhopal           8500.00
6   Komal      22        MP               4500.00
7   Muffy      24        Indore           10000.00

SET TRANSACTION Command

SET TRANSACTION command can be used to initiate a database transaction. This command is used to specify characteristics for the transaction that follows.

Syntax

Following is the syntax for SET TRANSACTION.

SET TRANSACTION ISOLATION LEVEL <Isolationlevel_name>

T-SQL – Indexes

Indexes are special lookup tables that the database search engine can use to speed up data retrieval. Simply put, an index is a pointer to data in a table. An index in a database is very similar to an index at the end of a book.

For example, if you want to reference all the pages in a book that discuss a certain topic, you first refer to the index, which lists all topics alphabetically and are then referred to one or more specific page numbers.

An index helps speed up SELECT queries and WHERE clauses, but it slows down data input, with UPDATE and INSERT statements. Indexes can be created or dropped with no effect on the data.

Creating an index involves the CREATE INDEX statement, which allows you to name the index, to specify the table and which column or columns to index, and to indicate whether the index is in ascending or descending order.

Indexes can also be unique, similar to the UNIQUE constraint, in that the index prevents duplicate entries in the column or combination of columns on which there”s an index.

CREATE INDEX Command

Following is the basic syntax of CREATE INDEX.

Syntax

CREATE INDEX index_name ON table_name

Single-Column Indexes

A single-column index is one that is created based on only one table column. Following is the basic syntax.

Syntax

CREATE INDEX index_name
ON table_name (column_name)

Example

CREATE INDEX singlecolumnindex
ON customers (ID)

Unique Indexes

Unique indexes are used not only for performance, but also for data integrity. A unique index does not allow any duplicate values to be inserted into the table. Following is the basic syntax.

Syntax

CREATE UNIQUE INDEX index_name
on table_name (column_name)

Example

CREATE UNIQUE INDEX uniqueindex
on customers (NAME)

Composite Indexes

A composite index is an index on two or more columns of a table. Following is the basic syntax.

Syntax

CREATE INDEX index_name on table_name (column1, column2)

Example

CREATE INDEX compositeindex
on customers (NAME, ID)

Whether to create a single-column index or a composite index, take into consideration the column(s) that you may use very frequently in a query”s WHERE clause as filter conditions.

Should there be only one column used, a single-column index should be the choice. Should there be two or more columns that are frequently used in the WHERE clause as filters, the composite index would be the best choice.

Implicit Indexes

Implicit indexes are indexes that are automatically created by the database server when an object is created. Indexes are automatically created for primary key constraints and unique constraints.

DROP INDEX Command

An index can be dropped using MS SQL SERVER DROP command. Care should be taken when dropping an index because performance may be slowed or improved.

Syntax

Following is the basic syntax.

DROP INDEX tablename.index_name

When to Avoid Indexes?

Although indexes are intended to enhance the performance of databases, there are times when they should be avoided. The following guidelines indicate when the use of an index should be reconsidered −

• Indexes should not be used on small tables.

• Tables that have frequent, large batch update or insert operations should not be indexed.

• Indexes should not be used on columns that contain a high number of NULL values.

• Columns that are frequently manipulated should not be indexed.

T-SQL – Functions

MS SQL Server has many built-in functions to perform processing on string or numeric data. Following is the list of all useful SQL built-in functions −

• − The SQL Server COUNT aggregate function is used to count the number of rows in a database table.

• − The SQL Server MAX aggregate function allows to select the highest (maximum) value for a certain column.

• − The SQL Server MIN aggregate function allows to select the lowest (minimum) value for a certain column.

• − The SQL Server AVG aggregate function selects the average value for certain table column.

• − The SQL Server SUM aggregate function allows selecting the total for a numeric column.

• − This is used to generate a square root of a given number.

• − This is used to generate a random number using SQL command.

• − This is used to concatenate multiple parameters to a single parameter.

• − Complete list of SQL functions required to manipulate numbers in SQL.

• − Complete list of SQL functions required to manipulate strings in SQL.

Select ASCII (''word'')

Select CHAR(97)

Select NCHAR(300)

Select CHARINDEX(''G'', ''KING'')

Select LEFT(''WORLD'', 4)

Select RIGHT(''INDIA'', 3)

Select SUBSTRING (''WORLD'', 1,3)
Select SUBSTRING (''INDIA'', 3,3)
Select SUBSTRING (''KING'', 2,3)

Select LEN(''HELLO'')

Select LOWER(''SQLServer'')

Select UPPER(''SqlServer'')

Select LTRIM(''   WORLD'')

Select RTRIM(''INDIA   '')

Select REPLACE(''INDIA'', ''I'', ''K'')

Select REPLICATE(''WORLD'', 2)

Select REVERSE(''WORLD'')

Select SOUNDEX(''Smith''), SOUNDEX(''Smyth'')

Select Difference(''Smith'',''Smyth'')

Select ''I''+space(1)+''LOVE''+space(1)+''INDIA''

Select STUFF(''ABCDEFGH'', 2,4,''IJK'')

Select STR(187.369,6,2)

Select UNICODE(''RAMA'')

Select QUOTENAME(''RAMA'',''"'')

Select PATINDEX(''I%'',''INDIA'')

SELECT FORMAT ( getdate(), ''D'')

Select CONCAT(''A'','','',''B'','','',''C'')

GETDATE()

Select getdate() as currentdatetime

DATEPART(datepart, datecolumnname)

Select datepart(day, getdate()) as currentdate

Select datepart(month, getdate()) as currentmonth

DATEADD(datepart, number, datecolumnname)

Select dateadd(day, 10, getdate()) as after10daysdatetimefromcurrentdatetime

DATEDIFF(datepart, startdate, enddate)

Select datediff(hour, 2015-11-16, 2015-11-11) as
differencehoursbetween20151116and20151111

CONVERT(datatype, expression, style)

SELECT CONVERT(VARCHAR(19),GETDATE())
SELECT CONVERT(VARCHAR(10),GETDATE(),10)
SELECT CONVERT(VARCHAR(10),GETDATE(),110)

Select ABS(-22)

Select ACOS(0)

Select ASIN(0)

Select ATAN(0)

Select ATN2(0, -1)

ID  NAME       AGE       ADDRESS             SALARY
1   Ramesh     32        Ahmedabad           2000.00
2   Khilan     25        Delhi               1500.00
3   kaushik    23        Kota                2000.00
4   Chaitali   25        Mumbai              6500.00
5   Hardik     27        Bhopal              8500.00
6   Komal      22        MP                  4500.00
7   Muffy      24        Indore              10000.00

SELECT salary from customers where salary between 2000 and 8500

salary
2000.00
2000.00
6500.00
8500.00
4500.00

Select MIN(salary)from CUSTOMERS

Select MAX(salary)from CUSTOMERS

Select SQRT(4)

Select PI()

Select CEILING(123.25)

Select FLOOR(123.25)

Select LOG(1)