Welcome back to another beginner tutorial. In my Previous tutorial I have explained you about basic SQL. In this tutorial, I will give you brief about Transact-SQL(T-SQL).
These are some differences as well as similarities between T-SQL and SQL. T-SQL is an enhanced version of SQL. In T-SQL we have SQL along with programming concepts.(SQL + Programming = T-SQL). T-SQL have most of the programming concepts like variables, loops, conditions, etc..
Note: Oracle as has the similar concept known as PL/SQL
Simply variable is buckets where you can store values. T-SQL support variables. You can use a variable to assign values, change values when you need. In T-SQL variables declare, assign values, retrieving values as below as below.
--Syntex: ---declaration DECLARE @variable data-type ---Assignment SET @variable='value' ---Retrieve SELECT @variable --Example DECLARE @MyName varchar(20) SET @MyName='Aravind' SELECT @MyName
When we execute SQL statement the will execute one by one. But in T-SQL we have a facility to execute a bunch of statement at a time. Known as Batch Execution. The main use of this is performance. Also if any one statement has syntactical error in any one statement, none of the statement will execute.
--example USE StudentDb INSERT INTO Student(name,email) VALUES ('aravind','firstname.lastname@example.org'); SELECT * FROM Student; GO
In programming world
IF....ELSE is the basic conditional control. Have a look at the below example how we can use
IF....ELSE in T-SQL.
DECLARE @temp char(2) SELECT @temp = Gender FROM Student WHERE StudentId=333 IF @temp='M' PRINT 'Hi Handsome. How are you today?' ELSE PRINT 'Hi beautiful. How are you today?'
BEGIN, END keyword are much like open and close parenthesis we use in high-level programming languages. Mostly we use these in condition statement where we have more than one statement to execute. See the example
IF (SELECT COUNT(*) FROM Student WHERE Gender = 'M') > 0 BEGIN PRINT 'This is a boys college' PRINT ' ' SELECT fname, lname FROM Student END ELSE PRINT 'No boys'
WHILE is used to repeatedly execute statements until the condition became false. There are many advantages of using while in T-SQL. See this example.
DECLARE @counter INT,@total INT SET @counter=0 SET @total=SELECT COUNT(*) FROM Student WHERE lname="Gates" WHILE (@counter < @total) BEGIN UPDATE Student SET lname= lname + CAST(@counter as char(2)) WHERE lname="Gates" SET @counter = @counter+1 END
In this example, we finding all record with the last name as Gates and updating them with count appending to them.
In programming, we use case instead of multiple nested if..else statements. Similarly, we use CASE to evaluate an express whether it is true or false based on it uses specific values.
SELECT latitude , 'For Country' = CASE WHEN 'AF' THEN 'Afghanistan' WHEN 'IN' THEN 'India' WHEN 'RU' THEN 'Russia' WHEN 'US' THEN 'United States' WHEN 'LK' THEN 'Sri Lanka' END FROM Country
Transactions are much like a batch. The only difference between Transaction and batch is we can undo all changes we made by statements within the single translations. We can not do this in Batch. We use COMMIT TRANSACTION or ROLLBACK TRANSACTION statement at the end. If we put ROLLBACK TRANSACTION it will undo all the changes.
BEGIN TRANSACTION SELECT * FROM Student ...... COMMIT TRANSACTION
8) Stored Procedures
Stored Procedures are a most Important concept in databases. There are many advantages using stored procedures. Mainly performance because sorted procedures are compiled and will be cached after the first time we used it. Another big advantage is we can call stored procedures from programming languages like vb,c#.
CREATE PROCEDURE uspGetStudent @sname nvarchar(50) AS SELECT fname,lname,rolno FROM Student WHERE fname = @sname GROUP BY fname ORDER BY fname GO --Execute stored procedure EXEC usp 'aravind' GO
These are very basic concepts of T-SQL. There are some advanced concepts like Views,Triggers,etc...