7 SQL - Alias.txt

 Aliases:

SQL aliases are used to give a table, or a column in a table, a temporary name.

Aliases are often used to make column names more readable.

An alias only exists for the duration of that query.

An alias is created with the AS keyword.

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Column Alias:

----Simple select 
	 select id as demoid, name as demoname from demo1;
	select id "demoid", name "demoname" from demo1;


----With Where clause
	select id AS demoID, NAme AS DemoName from demo1 where age IS NOT NULL;


TABLE Alias:

----To fetch records from two tables.	


	----Without Where clause
	this is used when both tables have same column name.	
	**** when both tables have same column
	 SELECT d1.Id, d2.NAME FROM demo1 d1, demo2 d2;
	(Say, demo1 has 4 and demo2 5 records result will be 20 records(4*5) i.e each record of demo1*each record of demo2).

	**** when both tables have different column names(no need of alias)
	SELECT age, new FROM demo1, demo2;

NOTE: There should not be ambiguity in column names
	if same name column occurs, we use alis

	----With Where clause

         SELECT C.ID, C.NAME, O.NAME FROM demo1 C, demo2 O WHERE  C.ID = O.ID;