Table-valued functions and Scalar-valued functions in SQL Server

As the name suggests: table-valued returns table, however Scalar-valued returns a single value, such as a string, integer, or bit value.

1、table-valued function

As to create table-valued function, there are 2 ways, look at the example below please, it’s suitable for simple logic:

USE Redgate
CREATE  TABLE DBO.TestCount_1(ID int,C1 VARCHAR(400),C2 VARCHAR(300),C3 VARCHAR(150) NOT NULL,C4 VARCHAR(80),C5 VARCHAR(38) NOT NULL)
CREATE  TABLE DBO.TestCount_2(ID int,C1 VARCHAR(400),C2 VARCHAR(300),C3 VARCHAR(150) NOT NULL,C4 VARCHAR(80),C5 VARCHAR(38) NOT NULL)
DECLARE @COUNT INT =1
SET NOCOUNT ON
WHILE @COUNT<=150
BEGIN
    INSERT DBO.TestCount_1(ID, C1, C2, C3, C4, C5)
        SELECT @COUNT,NEWID(),NEWID(),NEWID(),NEWID(),NEWID()
    INSERT DBO.TestCount_2(ID, C1, C2, C3, C4, C5)
        SELECT @COUNT,NEWID(),NEWID(),NEWID(),NEWID(),NEWID()
    SET @COUNT=@COUNT+1
END

Create funcation

USE Redgate;
GO
CREATE FUNCTION DBO.TestCount (@ID int)
RETURNS TABLE
AS
RETURN 
(
    SELECT A.* FROM DBO.TestCount_1 A,DBO.TestCount_2 B
        WHERE A.ID =B.ID AND A.ID=@ID
);
GO

You can use below statement to query:

SELECT *  FROM TestCount(5)

For more complex logic, more statements, you can use another table-valued function, look at the example below:

USE Redgate;
GO
CREATE FUNCTION dbo.TestCount_Complex (@ID int)
RETURNS @Return_TestCount TABLE 
(
    ID int,
    C1 VARCHAR(38),
    C2 VARCHAR(38),
    C3  VARCHAR(38)
)
AS
BEGIN
   INSERT INTO @Return_TestCount(ID,C1,C2,C3)
        SELECT ID,C1,C2,C3 FROM DBO.TestCount_1 WHERE ID=@ID
   INSERT INTO @Return_TestCount(ID,C1,C2,C3)
        SELECT ID,C1,C2,C3 FROM DBO.TestCount_2 WHERE ID=@ID
   RETURN
END;
GO

Use this statement to call the function:

SELECT * FROM TestCount_Complex(5)

2、Scalar-valued functions

It’s easy than table-valued function, look the sample:

CREATE FUNCTION [dbo].TestCount_SVF
(
    @ID int
)
RETURNS VARCHAR(50)
AS
BEGIN
    declare @nodeCount VARCHAR(50)
    select @nodeCount=C2 from TestCount_1 WHERE  ID=@ID
    return @nodeCount
END

--SELECT DBO.TestCount_SVF(5)

Mark:

1、table-valued function can join table, but Scalar-valued functions can not join table.

SELECT *  FROM TestCount(5) A,TestCount_1 B WHERE A.ID=B.ID

2、table-valued function can not nest in table, but Scalar-valued functions can do it.

SELECT DBO.TestCount_SVF(5), * FROM TestCount_1

3、call table-valued function is :

SELECT *  FROM TestCount(5)

but Scalar-valued functions is:

SELECT DBO.TestCount_SVF(5)

4、if their schema is dbo, call table-valued function can:

SELECT *  FROM TestCount(5)

but Scalar-valued functions must add “dbo”:

SELECT DBO.TestCount_SVF(5)