SQL - WHERE Clause

The SQL WHERE clause is used to specify a condition while fetching the data from single table or joining with multiple table.
If the given condition is satisfied then only it returns specific value from the table. You would use WHERE clause to filter the records and fetching only necessary records.
The WHERE clause not only used in SELECT statement, but it is also used in UPDATE, DELETE statement etc. which we would examine in subsequent chapters.

Syntax:

The basic syntax of SELECT statement with WHERE clause is as follows:

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

You can specify a condition using comparision or logical operators like >, <, =, LIKE, NOT etc. Below examples would make this concept clear.

Example:

Consider CUSTOMERS table is having 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 is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000:

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

This would produce following result:

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

Following is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table for a customer with name Hardik. Here it is important to note that all the strings should be given inside single quotes ('') where as numeric values should be given without any quote as in above example:

SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE NAME = 'Hardik';

This would produce following result:

+----+----------+----------+
| ID | NAME     | SALARY   |
+----+----------+----------+
|  5 | Hardik   |  8500.00 |
+----+----------+----------+