Coalesce function

Coalesce function returns the first non-null value among the arguments.

Syntax:

Coalesce (expression [,..n])

Here is example using Coalesce function

Example 1

DECLARE @Str1 varchar(10),@str2 varchar(20),@Str3 varchar(20)

SET @Str2='Sql' , @Str3='Server'

SELECT COALESCE(@Str1,@str2,@Str3) As [Coalesce]

In above example @Str2 value is ‘Sql’ , @str3 value is ‘Server’  and @str1 values is Null because it not assigned any value .

Output:

It return’s “Sql” because Coalesce function return’s first non null value.

Example 2:

Coalesce in select statement.

IF OBJECT_ID('Employee','U') IS NOT NULL

DROP TABLE Employee

CREATE TABLE Employee

(

  ID INT IDENTITY(1,1) PRIMARY KEY ,

  NAME VARCHAR(20),

  SALARY INT

)

INSERT INTO Employee  (NAME,SALARY) VALUES ('Rakesh',5000),(NULL,6000),('Naresh',7000) ,(NULL,8000)

SELECT * FROM Employee

In above Query Result ID 2, 4 of Name Column is null.   We have to replace Name Column null value to some other value (“Madhu”) using select statement.

SELECT ID,COALESCE(NAME,'Madhu') AS Name,SALARY FROM Employee

Output:

Example 3:

Coalesce in where condition.

DECLARE @Lod_ID int =null

SET @Lod_ID =3

SELECT * FROM Employee where ID= COALESCE(@Lod_ID,ID)

Output:

It only select ID value 3 row .because of in above @Lod_ID variable is set to 3 values . Coalesce funtion returns first non-null value baecuse it’s selects only 3 of ID colums rows only.  

Example 4:

DECLARE @Lod_ID int =null

SELECT * FROM Employee where ID= COALESCE(@Lod_ID,ID)

In above example if we are not set any value to @Lod_ID variable . we are get all row from Employee table .