Defensive Database Programming - Red Gate Software

Chapter 2: Code Vulnerabilities due to SQL Server MisconceptionsSELECT @i AS [@i after the assignment] ;Listing 2-12: SELECT may leave a variable unchanged if it raises an error.Understanding how SET and SELECT behave is very important. In particular, thebehavior of SELECT demonstrated in Listing 2-9, whereby it leaves a variable unchangedif the selected result set is empty, can lead to the dreaded infinite loop.Use set-based solutions where possibleOf course, wherever possible we should avoid procedural, row-by-row processing inour T-SQL code, in favor of proper set-based aggregation. However, sometimes loopsare unavoidable.In order to demonstrate the infinite loop problem, create the Orders table shown inListing 2-13 and populate it with sample data.CREATE TABLE dbo.Orders(OrderID INT NOT NULL ,OrderDate DATETIME NOT NULL ,IsProcessed CHAR(1) NOT NULL ,CONSTRAINT PK_Orders PRIMARY KEY ( OrderID ) ,CONSTRAINT CHK_Orders_IsProcessedCHECK ( IsProcessed IN ( 'Y', 'N' ) )) ;GOINSERT dbo.Orders( OrderID ,OrderDate ,IsProcessed)SELECT 1 ,'20090420' ,'N'UNION ALL67