SQL SQRT() 函數(shù)

SQL SQRT 函數(shù)

　SQRT 函數(shù)用于計(jì)算得出任何數(shù)值的平方根。你可以像下面這樣使用 SELECT 語(yǔ)句計(jì)算任何數(shù)值的平方根：

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

　你在這里看到的是浮點(diǎn)數(shù)，因?yàn)?SQL 以浮點(diǎn)數(shù)類(lèi)型來(lái)進(jìn)行平方根的計(jì)算。

　你還可以使用 SQRT 函數(shù)來(lái)計(jì)算表中記錄的平方根。要獲得對(duì) SQRT 函數(shù)更深入的了解，請(qǐng)考慮 employee_tbl 表，表中記錄如下所示：

    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)

　現(xiàn)在，假設(shè)你想要獲取每個(gè)記錄中 daily_typing_pages 的平方根，那么你可以用如下命令來(lái)達(dá)到目的：

    SQL> 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)