WHERE Clause in SQL

Where clause is used when we need to fetch a particular row or set of rows from a table. This clause defines the condition and only those rows(s) comes out as result that satisfies the condition defined in WHERE clause of the SQL query.

Syntax:

SELECT Coulmn_name1, Column_name2, .... 
FROM Table_name
WHERE Condtion;

Example

Lets say this is the content of my table EMPLOYEES:

+------+----------+---------+----------+
|SSN   | EMP_NAME | EMP_AGE |EMP_SALARY|
+------+----------+---------+----------+
|  101 | Steve    |  23     |  9000.00 |
|  223 | Peter    |  24     |  2550.00 |
|  388 | Shubham  |  19     |  2444.00 |
|  499 | Chaitanya|  29     |  6588.00 |
|  589 | Apoorv   |  21     |  1400.00 |
|  689 | Rajat    |  24     |  8900.00 |
|  700 | Ajeet    |  20     | 18300.00 |
+------+----------+---------+----------+

Now If I need to fetch the name of the employees who are having age greater than 23 then I would be writing the SELECT Query like this:

SELECT EMP_NAME 
FROM EMPLOYEES
WHERE EMP_AGE > 23;

Output:

+----------+
| EMP_NAME | 
+----------+
| Peter    | 
| Chaitanya|  
| Rajat    | 
+----------+

Lets say I want to find out the SSN of Ajeet. I can do it like this:

SELECT SSN, EMP_NAME
FROM EMPLOYEES
WHERE EMP_NAME = 'Ajeet';

Output:

+------+----------+
|SSN   | EMP_NAME | 
+------+----------+
|  700 | Ajeet    | 
+------+----------+

All the details of employees having salary greater than 6000.

SELECT * 
FROM EMPLOYEES
WHERE EMP_SALARY > 6000;

Result:

+------+----------+---------+----------+
|SSN   | EMP_NAME | EMP_AGE |EMP_SALARY|
+------+----------+---------+----------+
|  101 | Steve    |  23     |  9000.00 |
|  499 | Chaitanya|  29     |  6588.00 |
|  689 | Rajat    |  24     |  8900.00 |
|  700 | Ajeet    |  20     | 18300.00 |
+------+----------+---------+----------+