SQL-JOIN来自两个表的两个列

Question

我需要帮助来制定查询。 我想从表A和表B中选择所有DISTINCT颜色。

这是查询的结果：

BLACK
RED
YELLOW
BLUE

我有这些表：

表A

ID   NAME    COLOR
5    SOCKS   BLACK
4    SOCKS   RED

表B

ID   NAME   COLOR 
0    CAR    BLUE
1    BIKE   BLUE
5    TRUCK  YELLOW
10   PLANE  NULL

我努力了：

SELECT DISTINCT A.color FROM A JOIN B ON b.color

但是我没有得到所有的颜色。 :(

Answer 1

SELECT color FROM A
UNION
SELECT color FROM B
WHERE  color IS NOT NULL -- only filters NULL from B
ORDER  BY color          -- sorts all rows

UNION （而不是UNION ALL ）删除重复项。 无需其他子查询或DISTINCT 。

Answer 2

SELECT 
  A.Color FROM TableA A
WHERE A.Color IS NOT NULL
UNION
SELECT
  B.Color FROM TableB B
    WHERE B.Color IS NOT NULL

我删除了DISTINCT，因为将它与UNION结合使用时没有必要-我总是会忘记这一点！

Answer 3

尝试：

SELECT DISTINCT Color
FROM (
    SELECT Color FROM TableA
    UNION ALL
    SELECT Color FROM TableB
) Colors
WHERE NOT Color IS NULL

Answer 4

http://sqlfiddle.com/#!2/0de4d/5

SELECT distinct
    COLOR
FROM
    (
      select color from TableA
      UNION
      select color from TableB
    ) tmp
WHERE color IS NOT NULL
order by color

编辑以删除空值

全面披露-SQL Fiddle是我的网站

Answer 5

SELECT DISTINCT color FROM 
(
    (
        (SELECT color FROM A WHERE color IS NOT NULL)
        UNION 
        (SELECT color FROM B WHERE color IS NOT NULL)
    ) AS temp
)