SQL WHERE Clause
The
SQL 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, 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 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:
SELECT
column1, column2, columnN
FROM
table_name
WHERE
[condition]
You
can specify a condition using comparison or logical operators like >, <,
=, LIKE, NOT etc. Below examples would 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
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 the 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 the following result:
+----+----------+------------+
|
ID | NAME | SALARY |
+----+----------+------------+
|
5 | Hardik | 8500.00 |
+----+----------+------------+
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