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:
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 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 | Ramakrishna | 32 | Ahmedabad | 2000.00 |
| 2 | Mdhu sudhan rao | 25 | Delhi | 1500.00 |
| 3 | Sai | 23 | Kota | 2000.00 |
| 4 | Kishor | 25 | Mumbai | 6500.00 |
| 5 | Ranjith | 27 | Bhopal | 8500.00 |
| 6 | Abhi | 22 | MP | 4500.00 |
| 7 | Kumar | 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:
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SQL> SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE SALARY > 2000;
This would produce the following result:
+----+----------+----------+
| ID | NAME | SALARY |
+----+----------+----------+
| 4 | Kishor | 6500.00 |
| 5 | Ranjith | 8500.00 |
| 6 | Abhi | 4500.00 |
| 7 | Kumar | 10000.00 |
+----+----------+----------+
Following is an example, which would fetch ID, Name and
Salary fields from the CUSTOMERS table for a customer
with name Ranjith . 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 = 'Ranjith ';
This would produce the following result:
+----+----------+----------+
| ID | NAME | SALARY |
+----+----------+----------+
| 5 | Ranjith | 8500.00 |
+----+----------+----------+
