[英]DB2 SQL select count over union of multiple tables
我需要返回多个表中某个条件的记录数
select count(*) c from table1
where exists (select * from crosstable where crosstable.refid = table1.id)
and crosstable.year = 2014
union
select count(*) c from table2
where exists (select * from crosstable where crosstable.refid = table2.id)
and crosstable.year = 2014
union
select count(*) c from table3
where exists (select * from crosstable where crosstable.refid = table3.id)
and crosstable.year = 2014
这给我返回了表中唯一整数值的结果集。
因此,如果table1返回'1',而table2和table3返回'5',我得到的是'1','5',而不是'1','5','5'。
而且它似乎不起作用
select sum(c) from (previous query))
我尝试使用sysdummy表,但语法不正确,因此找不到任何解决此问题的好例子。 可能是我正在完全错误地处理它。
最后,我需要将结果设为1个单一数字,这就是并集部分中每个子查询的计数
您的查询
select sum(c) from (previous query)
很好-差不多了。 DB2期望子查询具有别名,因此请尝试:
select sum(c) from (previous query) x
顺便说一下,您的union
几乎肯定需要成为union all
。 union
消除重复。
请在下面尝试
with temp as (
select count(*) c from table1
where exists (select * from crosstable where crosstable.refid = table1.id)
and crosstable.year = 2014
union all
select count(*) c from table2
where exists (select * from crosstable where crosstable.refid = table2.id)
and crosstable.year = 2014
union all
select count(*) c from table3
where exists (select * from crosstable where crosstable.refid = table3.id)
and crosstable.year = 2014
)
select sum(c) as final_count from temp;
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