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Category: mysql
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Khóa học miễn phí MySQL – Indexes nhận dự án làm có lương
MySQL – INDEXES
An index is a data structure that improves the speed of operations on a database table. They are a special type of lookup tables pointing to the data. Indexes can be created on one or more columns, providing the basis for both rapid random lookups and efficient ordering of access to records.
Indexes, however, reduce the efficiency of INSERT and UPDATE operations on a table. This is because when we insert or update a data value in a table, indexes also need to be modified accordingly. So, they are not always appropriate to use.
Users cannot see the indexes, they are just used to speed up queries and will be used by the Database Search Engine to locate records very fast.
Types of MySQL Indexes
Indexes can be defined on single or multiple columns of a MySQL table. The decision to add indexes on a table column(s) depends on the type of data that needs to be searched. MySQL provides the following types of indexes −
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Simple Index
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Unique Index
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Primary Key Index
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Fulltext Index
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Descending Index
Simple Index
A simple index is a basic type of index where the values inserted into the column, containing this index, are searched easily. In such case, the column can contain duplicate values or NULL.
Unique Index
A Unique index does not allow any duplicate values to be inserted into a table column (where the index is defined on).It can be added to single or multiple columns of a table. If it is added to a single column, the values of that column must be unique. But if it is added to multiple columns, the combination of values in these columns must be unique.
Primary Key Index
Primary Key Index is an extension of unique index, as the primary key column must always contain unique values and these values must not be NULL. Primary key can be set to a single column of a database table, or multiple columns as well (which is not recommended).
Fulltext Index
In a database, sometimes you would have to search for a blob of text instead of a record. You can use fulltext index for it. As its name suggests, it is used to make the text searches in a table easier.
Descending Index
The descending index is only available in MySQL versions after 8.0. It is simple index used to store data in a reverse order. Using this index, it is easy to search for the latest values inserted into the database table.
Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc
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Khóa học miễn phí MySQL – Rename Views nhận dự án làm có lương
MySQL – Rename View
Renaming Views in MySQL
The MySQL RENAME TABLE statement in MySQL is generally used to rename the name of a table. But this statement can also be used to rename views because views are typically virtual tables created by a query.
Before renaming a view, we need to ensure that no active transactions are being performed on the view using its old name. It is, however, recommended to delete the existing view and re-create it with a new name instead of renaming it.
Syntax
Following is the basic syntax of the RENAME TABLE query to rename a view in MySQL −
RENAME TABLE original_view_name TO new_view_name;
Example
First of all, let us create a table with the name CUSTOMERS using the following query −
CREATE TABLE CUSTOMERS( ID int NOT NULL, NAME varchar(20) NOT NULL, AGE int NOT NULL, ADDRESS varchar(25), SALARY decimal(18, 2), PRIMARY KEY (ID) );
Here, we are inserting some records into the above-created table using the query below −
INSERT INTO CUSTOMERS VALUES (1, ''Ramesh'', ''32'', ''Ahmedabad'', 2000), (2, ''Khilan'', ''25'', ''Delhi'', 1500), (3, ''Kaushik'', ''23'', ''Kota'', 2500), (4, ''Chaitali'', ''26'', ''Mumbai'', 6500), (5, ''Hardik'',''27'', ''Bhopal'', 8500), (6, ''Komal'', ''22'', ''MP'', 9000), (7, ''Muffy'', ''24'', ''Indore'', 5500);
Creating a view −
Now, let us create a view based on the above created table using the following query −
CREATE VIEW CUSTOMERS_VIEW AS SELECT * FROM CUSTOMERS;
The view will be created 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 | Hyderabad | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
Renaming the view −
Now, we know that we are having an existing view in our database named “CUSTOMERS_VIEW”. So, we are going to rename this view to VIEW_CUSTOMERS using the below query −
RENAME TABLE CUSTOMERS_VIEW TO VIEW_CUSTOMERS;
Verification
Using the following SELECT statement, we can verify whether the view is renamed or not −
SELECT * FROM VIEW_CUSTOMERS;
The “VIEW_CUSTOMERS” view displayed 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 | Hyderabad | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
Rules to be followed while Renaming Views
There are some rules and practices to ensure that the renaming process goes smoothly and one should follow them while renaming a view in MySQL. They are listed below:
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Avoid renaming system views: In MySQL, the system views are views that contain all the information about the database management system. It is recommended not to rename these views because it can cause issues with the functioning of the database.
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Update all references to the view: After renaming a view in MySQL, any stored procedures, triggers, or other database objects that reference the view will need to be updated to use the new name of the view. If we failed to update these references results in errors or issues with the functioning of the database system.
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Test thoroughly: It is important to test the renaming process thoroughly in the development or testing environment to make sure that all references to the view have been updated correctly.
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Use a consistent naming convention: While working with views in MySQL, it”s recommended to use a consistent naming convention. If you need to rename a view, follow the same naming convention you”ve used for other views in the database.
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Backup the database: Before renaming a view, it is recommended to have a backup of the database to make sure that you have a restore point.
Renaming a View Using a Client Program
Until now, we used an SQL statement to rename a view directly in the MySQL database. But, we can also perform the same rename operation on a view using another client program.
Syntax
To Rename a view into MySQL Database through a PHP program, we need to execute the RENAME statement using the mysqli function named query() as follows −
$sql = "RENAME TABLE first_view To tutorial_view"; $mysqli->query($sql);
To Rename a view into MySQL Database through a JavaScript program, we need to execute the RENAME statement using the query() function of mysql2 library as follows −
sql = "RENAME TABLE CUSTOMERS_VIEW TO VIEW_CUSTOMERS"; con.query(sql);
To Rename a view into MySQL Database through a Java program, we need to execute the RENAME statement using the JDBC function named executeQuery() as follows −
String sql = "RENAME TABLE first_view TO tutorial_view"; st.executeQuery(sql);
To Rename a view into MySQL Database through a python program, we need to execute the RENAME statement using the execute() function of the MySQL Connector/Python as follows −
rename_view_query = "RENAME TABLE tutorial_view TO new_tutorial_view" cursorObj.execute(rename_view_query)
Example
Following are the programs −
$dbhost = ''localhost
$dbuser = ''root
$dbpass = ''password
$dbname = ''TUTORIALS
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if ($mysqli->connect_errno) {
printf("Connect failed: %s
", $mysqli->connect_error);
exit();
}
// printf(''Connected successfully.
'');
// A view can be renamed by using the RENAME TABLE old_view_name TO new_view_name
$sql = "RENAME TABLE first_view To tutorial_view";
if ($mysqli->query($sql)) {
printf("View renamed successfully!.
");
}
if ($mysqli->errno) {
printf("View could not be renamed!.
", $mysqli->error);
}
$mysqli->close();
Output
The output obtained is as follows −
View renamed successfully!.
var mysql = require(''mysql2'');
var con = mysql.createConnection({
host: "localhost",
user: "root",
password: "Nr5a0204@123"
});
//Connecting to MySQL
con.connect(function (err) {
if (err) throw err;
console.log("Connected!");
console.log("--------------------------");
sql = "create database TUTORIALS"
con.query(sql);
sql = "USE TUTORIALS"
con.query(sql);
sql = "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));"
con.query(sql);
sql = "INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES (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 );"
con.query(sql);
//Creating View
sql = "Create view CUSTOMERS_VIEW AS SELECT * FROM CUSTOMERS";
con.query(sql);
//Renaming View
sql = "RENAME TABLE CUSTOMERS_VIEW TO VIEW_CUSTOMERS;"
con.query(sql);
//Displaying records from view
sql = "SELECT * FROM VIEW_CUSTOMERS;"
con.query(sql, function(err, result){
if (err) throw err
console.log("**Views after deleting:**");
console.log(result);
});
});
Output
The output produced is as follows −
Connected!
--------------------------
[
{ID: 1, NAME: ''Ramesh'', AGE: 32, ADDRESS: ''Ahmedabad'', SALARY: ''2000.00''},
{ID: 2, NAME: ''Khilan'', AGE: 25, ADDRESS: ''Delhi'', SALARY: ''1500.00''},
{ID: 3, NAME: ''kaushik'', AGE: 23, ADDRESS: ''Kota'', SALARY: ''2000.00''},
{ID: 4, NAME: ''Chaitali'', AGE: 25, ADDRESS: ''Mumbai'', SALARY: ''6500.00''},
{ID: 5, NAME: ''Hardik'', AGE: 27, ADDRESS: ''Bhopal'', SALARY: ''8500.00''},
{ID: 6, NAME: ''Komal'', AGE: 22, ADDRESS: ''MP'', SALARY: ''4500.00'' },
{ID: 7, NAME: ''Muffy'', AGE: 24, ADDRESS: ''Indore'', SALARY: ''10000.00''}
]
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class RenameView {
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/TUTORIALS";
String username = "root";
String password = "password";
try {
Class.forName("com.mysql.cj.jdbc.Driver");
Connection connection = DriverManager.getConnection(url, username, password);
Statement statement = connection.createStatement();
System.out.println("Connected successfully...!");
//Rename Created View.....
String sql = "RENAME TABLE first_view TO tutorial_view";
statement.executeUpdate(sql);
System.out.println("Renamed view Successfully...!");
ResultSet resultSet = statement.executeQuery("SELECT * FROM tutorial_view");
while (resultSet.next()) {
System.out.print(resultSet.getInt(1)+" "+ resultSet.getString(2)+ " "+ resultSet.getString(3));
System.out.println();
}
connection.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
Output
The output obtained is as shown below −
Connected successfully...! Renamed view Successfully...! 1 Learn PHP John Paul
import mysql.connector
#establishing the connection
connection = mysql.connector.connect(
host=''localhost'',
user=''root'',
password=''password'',
database=''tut''
)
cursorObj = connection.cursor()
rename_view_query = "RENAME TABLE tutorial_view TO new_tutorial_view"
cursorObj.execute(rename_view_query)
connection.commit()
print("View renamed successfully.")
cursorObj.close()
connection.close()
Output
Following is the output of the above code −
View renamed successfully.
Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc