Question

我有

table1：country，theOrderColumn1
table2：country，theOrderColumn2

我想从这两个SELECT语句中加入DISTINCT country：

SELECT DISTINCT `country` FROM `table1` ORDER BY `theOrderColumn1`

和

SELECT DISTINCT `country` FROM `table2` ORDER BY `theOrderColumn2`

示例：

table1 (country, theOrderColumn1): (uk, 1), (usa, 2)
table2 (country, theOrderColumn2): (france, 1), (uk, 2)

我想要这个结果：

france
uk
usa

Answer 1

select distinct country
from (
    select country, theOrderColumn from table1
    union all
    select country, theOrderColumn from table2
) a 
order by theOrderColumn

Answer 2

select country, theOrderColumn from (
select distinct t1.country as country, t1.theOrderColumn as theOrderColumn from table t1
union
select distinct t2.country as country, t2.theOrderColumn as theOrderColumn from table t2) t3
order by theOrderColumn

Answer 3

select a.country,a.theOrderColumn
(
select country,theOrderColumn
from table1
union
select country,theOrderColumn
from table2
) a
order by a.theOrderColumn

如果表1和表2中的OrderColumn不同，您将获得重复。

Answer 4

这取决于您的需求以及您希望如何将两个表连接在一起。如果您基于“theOrderColumn”加入，则查询将是

SELECT DISTINCT country 
FROM table1 
JOIN table2 ON table1.theOrderColumn = table2.theOrderColumn 
ORDER BY theOrderColumn

如果你想在全国范围内加入（由于两个表格中的国家相同而没有意义），那么你可以在连接条款中换掉“country”。

此外，根据您的DBMS所说的SQL方言，您的里程可能会因上述查询而异。你能澄清一下你所追求的更多内容吗？

Answer 5

如果要同时保留theOrderColumn1和theOrderColumn2给出的顺序，可以使用列索引指定ORDER BY列。

SELECT distinct country FROM(

  (SELECT country as c, theOrderColumn1 as d from table1
  UNION
  SELECT country as c, theOrderColumn2 as d from table2
  )
  order by 2
)

看看这个问题的答案：SQL Query - Using Order By in UNION

如何在一个查询中从2个表中选择不同的值并进行排序？

5 个答案: