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SQL COUNT function is the simplest function and very useful in counting the number of records which are expected to be returned by a SELECT statement.
To understand COUNT function consider an employee_tbl table which is having following records:
SQL> SELECT * FROM employee_tbl; +------+------+------------+--------------------+ | id | name | work_date | daily_typing_pages | +------+------+------------+--------------------+ | 1 | John | 2007-01-24 | 250 | | 2 | Ram | 2007-05-27 | 220 | | 3 | Jack | 2007-05-06 | 170 | | 3 | Jack | 2007-04-06 | 100 | | 4 | Jill | 2007-04-06 | 220 | | 5 | Zara | 2007-06-06 | 300 | | 5 | Zara | 2007-02-06 | 350 | +------+------+------------+--------------------+ 7 rows in set (0.00 sec) |
Now suppose based on the above table you want to count total number of rows in this table then you can do it as follows:
SQL>SELECT COUNT(*) FROM employee_tbl ; +----------+ | COUNT(*) | +----------+ | 7 | +----------+ 1 row in set (0.01 sec) |
Similarly you want to count the number of records for Zara then it can be done as follows:
SQL>SELECT COUNT(*) FROM employee_tbl -> WHERE name="Zara"; +----------+ | COUNT(*) | +----------+ | 2 | +----------+ 1 row in set (0.04 sec) |
NOTE: All the SQL queries are case insensitive so it does not make any difference if you give ZARA or Zara in WHERE CONDITION.
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