为什么查询语句中经常会有"1=1"

目的是动态查询，查询语句先加上WHERE 1=1，然后后面的条件不论是有一个或者多个都可以直接写为AND <condition>.

 

dim sqlstmt as new StringBuilder
sqlstmt.add("SELECT * FROM Products")
sqlstmt.add(" WHERE 1=1") 

''// From now on you don't have to worry if you must 
''// append AND or WHERE because you know the WHERE is there
If ProductCategoryID <> 0 then
  sqlstmt.AppendFormat(" AND ProductCategoryID = {0}", trim(ProductCategoryID))
end if
If MinimunPrice > 0 then
  sqlstmt.AppendFormat(" AND Price >= {0}", trim(MinimunPrice))
end if

 

 

 

http://stackoverflow.com/questions/242822/why-would-someone-use-where-1-1-and-conditions-in-a-sql-clause