Question

Suppose I want to get student summaries from a two tables: student, grade:

CREATE PROCEDURE prc_get_student_grade_summaries
    @studentIds [Integer_udtt] READONLY
AS
BEGIN
SELECT Name,
    func_GetGradeAForStudent()
FROM tbl_student AS tS
    INNER JOIN
    @studentIds AS tSI
    ON tS.Id = tSI.studentId   

Integer udtt is defined as this:

CREATE TYPE [Integer_udtt] AS  TABLE (
    [Id] INT NOT NULL,
    PRIMARY KEY CLUSTERED ([Id] ASC));

func_GetGradeAForStudent is something like select COUNT(*) from student where studentId = id AND grade = 1 — 1: A

The result I want is list of summary:

StudentId  Number of A
101   5
102   4
103   2

What is the correct way to pass in the studentId from @studentIds to the func_GetGradeAForStudent?

Answer 1

You can’t pass table-value parameters to UDF’s:

MSDN:

Limitations of Table-Valued Parameters

There are several limitations to table-valued parameters:

You cannot pass table-valued parameters to user-defined functions.

Table-valued parameters can only be indexed to support UNIQUE or PRIMARY KEY constraints. SQL Server does not maintain statistics on
table-valued parameters.

Table-valued parameters are read-only in Transact-SQL code. You cannot update the column values in the rows of a table-valued
parameter and you cannot insert or delete rows. To modify the data
that is passed to a stored procedure or parameterized statement in
table-valued parameter, you must insert the data into a temporary
table or into a table variable.

You cannot use ALTER TABLE statements to modify the design of table-valued parameters.

Since these are just a list of student Ids, one possibility would be to pass those Ids as a comma-separeted list of ids and use a split function to recreate a table from the comma-separeted list. There’s a ton of examples here on SO and elsewhere where you can find sample implementation of a split function.

Or even better, do everything inside your proc. I don’t really see the need for that function if all is doing is a select count(*)... You should be able to do everything inline, perhaps using a subselect as so:

CREATE PROCEDURE prc_get_student_grade_summaries
    @studentIds [Integer_udtt] READONLY
AS
BEGIN
SELECT Name,
    (select COUNT(*) from student where studentId = tSI.studentId AND grade = 1 ) as NumberOfAs
FROM tbl_student AS tS
    INNER JOIN
    @studentIds AS tSI
    ON tS.Id = tSI.studentId   

UPDATE

Sample split function that takes a comma-separated list and returns a table:

CREATE FUNCTION [dbo].[fnSplit](
    @sInputList VARCHAR(8000) -- List of delimited items
  , @sDelimiter VARCHAR(8000) = ',' -- delimiter that separates items
) RETURNS @List TABLE (item VARCHAR(8000))

BEGIN
DECLARE @sItem VARCHAR(8000)
WHILE CHARINDEX(@sDelimiter,@sInputList,0) <> 0
 BEGIN
 SELECT
  @sItem=RTRIM(LTRIM(SUBSTRING(@sInputList,1,CHARINDEX(@sDelimiter,@sInputList,0)-1))),
  @sInputList=RTRIM(LTRIM(SUBSTRING(@sInputList,CHARINDEX(@sDelimiter,@sInputList,0)+LEN(@sDelimiter),LEN(@sInputList))))

 IF LEN(@sItem) > 0
  INSERT INTO @List SELECT @sItem
 END

IF LEN(@sInputList) > 0
 INSERT INTO @List SELECT @sInputList -- Put the last item in
RETURN
END

And you call it like this: select * from fnSplit(@CommaSeparetedList,',');