SQL statement Query Results Merge UNION ALL usage

Organize other people's SQL

Presumably the idea is to use Union and UNION ALL

--Merge duplicate rows
SELECT * FROM A
Union
SELECT * FROM B

--Do not merge duplicate rows
SELECT * FROM A
UNION ALL
SELECT * FROM B

Sort by a field
--Merge duplicate rows
SELECT *
From (
SELECT * FROM A
Union
SELECT * from B) as T
Order BY Field name

--Do not merge duplicate rows
SELECT *
From (
SELECT * FROM A
UNION ALL
SELECT * from B) as T
Order BY Field name

SQL Server Edition
Select * FROM (
Select top 2 id,adddate,title,url from barticle where classid= ' 1 ' ORDER by adddate Desc) A
Union All
Select * FROM (
Select top 2 id,adddate,title,url from barticle where classid= ' 2 ' ORDER by adddate Desc) B
Union All
Select * FROM (
Select top 2 id,adddate,title,url from barticle where classid= ' 3 ' ORDER by adddate Desc) C
Union All
Select * FROM (
Select top 2 id,adddate,title,url from barticle where classid= ' 4 ' ORDER by adddate Desc) D

MySQL version
Select * FROM (
Select Id,adddate,title,url from barticle where classid= ' 1 ' ORDER by adddate desc limit 0,2) A
Union All
Select * FROM (
Select Id,adddate,title,url from barticle where classid= ' 2 ' ORDER by adddate desc limit 0,2) B
Union All
Select * FROM (
Select Id,adddate,title,url from Barticle where classid= ' 3 ' ORDER by adddate desc limit 0,2) C
Union All
Select * FROM (
Select Id,adddate,title,url from Barticle where classid= ' 4 ' ORDER by adddate desc limit 0,2) D
Http://blog.csdn.net/kemy88/archive/2007/02/28/1516913.aspx