Question

我的数据库中有3个表，这3个表有公共列。第1列为Name，第2列为printed，第3列为location。

我要做的是从这3张表中获取所有记录

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

像

这样的东西

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

这可用吗？

Answer 1

您可以使用union来达到目标。 Union附加单独查询的结果集：

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"

如果您想知道特定记录来自哪个表，请为每个查询添加一个常量字段：

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

Answer 2

如果所有3个表具有相同的结构：

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'

如果结构不同（即每个表中的不同列）：

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'

union必须返回相同数据类型的列，并按所选顺序返回它们，由第一个选择定义...如果您有重复项，UNION将删除它们。如果您想保留重复项，请改用UNION ALL。

从具有相同列的多个表中获取所有记录

2 个答案: