Question

嘿我正在尝试加入2个表，但左侧是映射到所有条目。我正在避免，因为我希望表合并但是NULL值应该是

testtable00：

ownership membership
Johnny    Active

testtable01：

pet petname
dog John
cat timmy
parrot Johns

当我像这样加入他们时：

SELECT * FROM (select * from testtable00 inner join testtable01) as u where u.ownership like "%John%";

ownership membership pet petname
Johnny   Active      dog John
Johnny   Active      parrot Johns

我想要实现的是

ownership membership pet petname
Johnny   Active      NULL NULL
NULL       NULL      dog John
NULL       NULL      parrot Johns

Answer 1

由于表之间没有关系，因此您不应该使用JOIN。您想要的结果看起来像UNION：

SELECT ownership, membership, NULL AS pet, NULL as petname
FROM testtable00
WHERE ownership like '%John%'
UNION ALL
SELECT NULL AS ownership, NULL AS membership, pet, petname
FROM testtable01
WHERE petname like '%John%'

Answer 2

如果第一个表中有多个匹配记录，则此查询会为您提供正确的顺序：

SELECT ownership, membership, pet, petname
FROM (
  SELECT ownership as x, membership as y, 1 as z,
         ownership, membership, null as pet, null as petname
  FROM testtable00
  UNION ALL
  SELECT ownership as x, membership as y, 2 as z,
         null, null, pet, petname
  FROM testtable00 u inner join testtable01
  where u.ownership like "%John%"
) x
ORDER BY x, y, z

演示：http://sqlfiddle.com/#!9/4eb63e/1

| ownership | membership |    pet | petname |
|-----------|------------|--------|---------|
|      John |     Active | (null) |  (null) |
|    (null) |     (null) |    dog |    John |
|    (null) |     (null) |    cat |   timmy |
|    (null) |     (null) | parrot |   Johns |
|    Johnny |     Active | (null) |  (null) |
|    (null) |     (null) |    dog |    John |
|    (null) |     (null) |    cat |   timmy |
|    (null) |     (null) | parrot |   Johns |

MySQL连接表而不重复每个表值

2 个答案: