从同一列中的多个表中获取所有记录

Question

我在我的数据库中有3个表，这3个表具有公共列。列＃1是Name，列＃2是printed，列＃3是location。

我试图做的是那些3个表

where printed = "NO" and location = "Submitted" 

像

select * 
from table1, table2, table3 
where printed = "NO" and Location = "Submitted" 

事情是这样可以让所有的记录？

Answer 1

如果所有3代表具有相同的结构：

select t1.* 
from table1 t1 
where printed = 'NO' and Location = 'Submitted' 
union 
select t2.* 
from table2 t2 
where printed = 'NO' and Location = 'Submitted' 
union 
select t3.* 
from table3 t3 
where printed = 'NO' and Location = 'Submitted' 

如果结构是不同的（在每个表中，即，不同的列）：

select t1.somecolumn, t1.someothercolumn, t1.etc 
from table1 t1 
where printed = 'NO' and Location = 'Submitted' 
union 
select t2.somecolumn, t2.someothercolumn, t2.etc 
from table2 t2 
where printed = 'NO' and Location = 'Submitted' 
union 
select t3.somecolumn, t3.someothercolumn, t3.etc 
from table3 t3 
where printed = 'NO' and Location = 'Submitted' 

联合必须返回相同数据类型的列，并按照第一选择定义的顺序返回它们。如果有重复项，UNION将删除它们。如果你想保留你的副本，请改用UNION ALL。

Answer 2

您可以使用union来实现结果。 Union追加单独的查询的结果集：

select name, printed, location from table1 where printed = "NO" and Location = "Submitted" 
union 
select name, printed, location from table2 where printed = "NO" and Location = "Submitted" 
union 
select name, printed, location from table3 where printed = "NO" and Location = "Submitted" 

如果你想知道从哪个表中特定的记录是从哪里来的，然后不断字段添加到每个查询：

select name, printed, location, "table1" as table_name from table1 where printed = "NO" and Location = "Submitted" 
...