SQL虚拟表应用三例

SQL虚拟表应用三例

 

SQL虚拟表是一种通过SELECT语句查询常量表达式形成的一个结果集，和数据库的视图、物理表、临时表都差不多。一旦这个虚拟表构造出来，就可以当作实际的表来查询。

 

环境：

Windows XP Professional 简体中文版

mysql-5.0.45-win32

 

应用三例：

 

1、求数字对会计大写的对应表。

SELECT *

  FROM (SELECT 0 AS CODE, '零' AS NAME

        UNION

        SELECT 1, '壹'

        UNION

        SELECT 2, '贰'

        UNION

        SELECT 3, '叁'

        UNION

        SELECT 4, '肆'

        UNION

        SELECT 5, '伍'

        UNION

        SELECT 6, '陆'

        UNION

        SELECT 7, '柒'

        UNION

        SELECT 8, '捌'

        UNION

        SELECT 9, '玖'

        UNION

        SELECT 10, '拾') AS RMBDX

 ORDER BY CODE ASC;

 

查询结果：

CODE    NAME

--------------

0       零

1       壹

2       贰

3       叁

4       肆

5       伍

6       陆

7       柒

8       捌

9       玖

10      拾

 

 

2、产生0~999之间的数字。

SELECT CAST(CONCAT(CONCAT(N1, N2), N3) AS UNSIGNED INTEGER) AS NUMS

  FROM (SELECT '0' AS N1

        UNION

        SELECT '1'

        UNION

        SELECT '2'

        UNION

        SELECT '3'

        UNION

        SELECT '4'

        UNION

        SELECT '5'

        UNION

        SELECT '6'

        UNION

        SELECT '7'

        UNION

        SELECT '8'

        UNION

        SELECT '9') AS NUM1,

       (SELECT '0' AS N2

        UNION

        SELECT '1'

        UNION

        SELECT '2'

        UNION

        SELECT '3'

        UNION

        SELECT '4'

        UNION

        SELECT '5'

        UNION

        SELECT '6'

        UNION

        SELECT '7'

        UNION

        SELECT '8'

        UNION

        SELECT '9') AS NUM2,

       (SELECT '0' AS N3

        UNION

        SELECT '1'

        UNION

        SELECT '2'

        UNION

        SELECT '3'

        UNION

        SELECT '4'

        UNION

        SELECT '5'

        UNION

        SELECT '6'

        UNION

        SELECT '7'

        UNION

        SELECT '8'

        UNION

        SELECT '9') AS NUM3

 ORDER BY NUMS ASC;

 

查询结果：

NUMS

---------

0

1

2

3

4

...

998

999

 

 

 

3、求0~999之间整数的二次方根（平方根）。

 SELECT NUMS AS SQUARE, ROUND(SQRT(NUMS)) AS BASIS

  FROM (SELECT CAST(CONCAT(CONCAT(N1, N2), N3) AS UNSIGNED INTEGER) AS NUMS

          FROM (SELECT '0' AS N1

                UNION

                SELECT '1'

                UNION

                SELECT '2'

                UNION

                SELECT '3'

                UNION

                SELECT '4'

                UNION

                SELECT '5'

                UNION

                SELECT '6'

                UNION

                SELECT '7'

                UNION

                SELECT '8'

                UNION

                SELECT '9') AS NUM1,

               (SELECT '0' AS N2

                UNION

                SELECT '1'

                UNION

                SELECT '2'

                UNION

                SELECT '3'

                UNION

                SELECT '4'

                UNION

                SELECT '5'

                UNION

                SELECT '6'

                UNION

                SELECT '7'

                UNION

                SELECT '8'

                UNION

                SELECT '9') AS NUM2,

               (SELECT '0' AS N3

                UNION

                SELECT '1'

                UNION

                SELECT '2'

                UNION

                SELECT '3'

                UNION

                SELECT '4'

                UNION

                SELECT '5'

                UNION

                SELECT '6'

                UNION

                SELECT '7'

                UNION

                SELECT '8'

                UNION

                SELECT '9') AS NUM3) AS TMP_TAB

 WHERE SQRT(NUMS) = ROUND(SQRT(NUMS))

 ORDER BY SQUARE ASC;

 

查询结果：

 

SQUARE  BASIS

------------------

0       0

1       1

4       2

9       3

16      4

25      5

36      6

49      7

64      8

81      9

100     10

121     11

144     12

169     13

196     14

225     15

256     16

289     17

324     18

361     19

400     20

441     21

484     22

529     23

576     24

625     25

676     26

729     27

784     28

841     29

900     30

961     31

 

---- 《完》。