SQL查詢與同一列的多個表

Question

我有15個表，它們都有列CreationDate和LastModifiedDate有一種方法來查詢所有表，並在表中查找空值。

這就是我想我必須做的，但不知道是否有更有效的方法或更簡單的方法做以下

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

您最初的查詢不會做你期待什麼。它在所有缺少值的行中進行交叉連接。這會導致大量數據（如果所有表都有多行）或根本沒有（如果沒有缺失行）。

我假設你想知道的表名裏的東西丟失：

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