從不止一個表中具有相同列的所有記錄

Question

我的數據庫中有3個表，這3個表具有公共列。 第1列是Name ，第2列是printed ，第3列是location 。

我想做的是從那3個表中獲取所有記錄

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

就像是

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

這可以嗎？

Answer 1

您可以使用union來實現結果。 Union追加單獨查詢的結果集：

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"

如果您想知道特定記錄來自哪個表，請向每個查詢添加一個常量字段：

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

Answer 2

如果所有三個表都具有相同的結構：

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'

如果結構不同（即每個表中的不同列）：

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'

聯合必須返回相同數據類型的列，並以所選順序（由第一個選擇項定義的順序）返回它們。如果有重復項， UNION將刪除它們。 如果要保留重復項，請改用UNION ALL 。