Question

我尝试了几种方法在表中为表中的唯一或不同数据选择多个列，包括以下查询：

SELECT
(SELECT GROUP_CONCAT(DISTINCT a) FROM TableName),
(SELECT GROUP_CONCAT(DISTINCT b) FROM TableName),
(SELECT GROUP_CONCAT(DISTINCT c) FROM TableName);

SELECT(a, b, c) FROM TableNamegroup by 'a' order by a asc;

SELECT DISTINCT a FROM TableName
UNION
SELECT DISTINCT b FROM TableName
UNION
SELECT DISTINCT c FROM TableName;

但它们要么不起作用，要么以我无法使用的格式返回信息。我需要的是这样的格式：

+--------------------+
| a    | b    | c    |
|--------------------|
| 1    | 1    | 1    |
| 2    | 2    | 2    |
| 3    | 3    | 3    |
   etc......

没有做个别查询，有没有办法做到这一点？

Answer 1

如果您需要三列，则select需要三列。如果您想要独特的组合：

select distinct a, b, c
from TableName;

这是你想要的吗？

我怀疑您需要三列中唯一ID的列表。您可以使用MySQL中的变量来执行此操作：

select rn, max(a) as a, max(b) as b, max(c) as c
from ((select @rna := @rna + 1 as rn, a, null as b, null as c
       from (select distinct a from TableName) t cross join
            (select @rna := 0) const
      ) union all
      (select @rnb := @rnb + 1 as rn, null, b, null
       from (select distinct b from TableName) t cross join
            (select @rnb := 0) const
      ) union all
      (select @rnc := @rnc + 1 as rn, null, null, c
       from (select distinct c from TableName) t cross join
            (select @rnc := 0) const
       group by c
      )
     ) abc
group by rn
order by rn;

以下是SQL Fiddle中的工作示例。

多个“SELECT DISTINCT”查询

1 个答案: