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》。
本文转自 leizhimin 51CTO博客，原文链接：http://blog.51cto.com/lavasoft/39109，如需转载请自行联系原作者
