SQL查询与同一列的多个表

Question

我有15个表，它们都有列CreationDate和LastModifiedDate有一种方法来查询所有表，并在表中查找空值。

这就是我想我必须做的，但不知道是否有更有效的方法或更简单的方法做以下

Select COUNT(*) FROM Table1, Table2, Table3 
WHERE table1.CreationDate IS NULL 
     OR table1.LastModifiedDate IS NULL 
     OR table2.CreationDate IS NULL 
     OR table2.LastModifiedDate IS NULL 
     OR table3.CreationDate IS NULL 
     OR table3.LastModifiedDate IS NULL 

Answer 1

select count(*) 
from (
    select CreationDate, LastModifiedDate from Table1 
    union all 
    select CreationDate, LastModifiedDate from Table2 
    union all 
    select CreationDate, LastModifiedDate from Table3 
) a 
where CreationDate is null or LastModifiedDate is null 

Answer 2

您最初的查询不会做你期待什么。它在所有缺少值的行中进行交叉连接。这会导致大量数据（如果所有表都有多行）或根本没有（如果没有缺失行）。

我假设你想知道的表名里的东西丢失：

select tablename, count(*), 
     sum(case when CreationDate is null then 1 else 0 end) as MissingCreationDate, 
     sum(case when LastModifiedDate is null then 1 else 0 end) as MissingLastModifiedDate 
from ((select 'table1' as tablename, CreationDate, LastModifiedDate 
     from Table1 
    ) union all 
     (select 'table2' as tablename, CreationDate, LastModifiedDate 
     from Table2 
    ) union all 
     . . . 
     (select 'table15', CreationDate, LastModifiedDate 
     from Table3 
    ) 
    ) t 
where CreationDate is null or LastModifiedDate is null 
group by tablename