MySQL的SQRT()函數是用來找出任何數的平方根。使用SELECT語句來查找出任何數的平方根如下：

mysql>  select SQRT(16);
+----------+
| SQRT(16) |
+----------+
| 4.000000 |
+----------+
1 row in set (0.00 sec)

在這裡所看到的浮點值，是MySQL的內部操作平方根以浮點數據類型返回。

也可以使用Sqrt()函數找出各種記錄平方根。要理解更詳細Sqrt()函數，考慮anemployee_tbl表，其具有以下記錄：

mysql> 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)

假設在上表基礎上，要計算所有dialy_typing_pages列的值的平方根，那麼可以使用下麵的命令：

mysql> SELECT name, SQRT(daily_typing_pages)
    -> FROM employee_tbl;
+------+--------------------------+
| name | SQRT(daily_typing_pages) |
+------+--------------------------+
| John |                15.811388 |
| Ram  |                14.832397 |
| Jack |                13.038405 |
| Jack |                10.000000 |
| Jill |                14.832397 |
| Zara |                17.320508 |
| Zara |                18.708287 |
+------+--------------------------+
7 rows in set (0.00 sec)