Dynamic SQL

"a programming technique that enables you to build SQL statements dynamically at runtime." -Oracle Docs

Dynamic SQL is a very useful tool but should only be used when absolutely necessary. Having SQL compiled at runtime amplifies the threat of SQL injection and the readability of the SQL code (dynamic SQL SPs result in large double and quadruple quoted red text which can make things much more difficult to read than when reading regular highlighted SQL code).

But when circumstances require you to use dynamic SQL to get the data you need (ie. there is no other way to structure your database environment and/or the "dynamism" can't be done equally as easy or easier using some sort of data adapter like .NET CLR code) dynamic SQL may be your best option.

For more in-depth info on this subject, see this great reference from SQL Server MVP Erland Sommarskog on this subject and the pros and cons of using dynamic SQL: http://www.sommarskog.se/dynamic_sql.html

Here is a brief example of dynamic SQL:

 DECLARE @mult bit = 0  
 DECLARE @sqlToExecute varchar(500)  
 DECLARE @srvWest varchar(50) = 'WestZoneSqlSrv08'  
 DECLARE @srvEast varchar(50) = 'EastZoneSqlSrv08'  
 IF @mult = 0  
      SET @sqlToExecute = 'SELECT TOP 1 OrderId, PersonId FROM ALGO.dbo.[Order]'  
 ELSE  
      SET @sqlToExecute = 'SELECT TOP 1 OrderId, PersonId FROM ' + @srvEast + '.ALGO.dbo.[Order] UNION ALL SELECT TOP 1 OrderID, PersonId FROM ' + @srvWest + '.ALGO.dbo.Order'   
 EXEC(@sqlToExecute)