Category Archives: sql

SQL – UNION Operator Table of content The SQL UNION Operator The SQL UNION operator is used to combine data from multiple tables by eliminating duplicate rows (if any). To use the UNION operator on multiple tables, all these tables must be union compatible. And they are said to be union compatible if and only […]

SQL – NOT NULL Constraint Table of content In a table, columns can typically accept NULL values by default. However, if you want to ensure that a particular column does not contain NULL values, you need to add the NOT NULL constraint/condition on that column. The SQL NOT NULL Constraint The NOT NULL constraint in […]

SQL – Group By Clause Table of content The SQL GROUP BY Clause The SQL GROUP BY clause is used in conjunction with the SELECT statement to arrange identical data into groups. This clause follows the WHERE clause in a SELECT statement and precedes the ORDER BY and HAVING clauses (if they exist). The main […]