SQL Server: efficiently search for many values on many to many columns? - sql

Question

I am creating a website using SQL Server. In the admin interface, I have two fields:
Subject: Math, English, History, ...
Grade: 1, 2, 3, 4, ...
Multiple values of a field can be assigned to a record.
Now in the frontend search, I would like a visitor to be able to select more than one value of a field for search. For example, someone may search for Subject being Math OR History and Grade being 1 OR 3.
What table design and SQL statement (or MS-proprietary statement) should I use to have efficient search?
Thanks and regards.
UPDATE
Thanks for all input!
I feel compelled to explain. I am technical and familiar with SQL. One thing I learned over my MANY years of programming experience is to be practical. For this question, I already have an initial design, but not sure how other folks to handle it for EFFICIENT SEARCH (there are always smarter folks out there). Here is my table design for storing a record:
Subject
type: varchar. record example: ,1,3, (each is the id of corresponding value)
Grade (this means applicable grade)
type: varchar. record example: ,1,2, (each is the id of corresponding values. this means a record is applicable to grade 1, 2)
Search example
where (subject LIKE '%,1,%' OR subject like '%,3,%') AND (grade like '%,1,%')
This design should lead to efficient search, but has drawbacks that it increases the complexity data management in the backend.
Another reason for my design is: the Subject and Grade each have a list of values that never/rarely change, and once a record is created, it never or rarely updates.
I am trying to strike a balance among simplicity, understandability, design, management, etc.

Answer 1

create table Subject (
SubjectId int identity(1, 1),
SubjectName nvarchar(255),
other fields.... )
create table GradingScale (
GradeId int identity(1, 1),
Grade int,
Description varchar(25),
other fields... )
create table Students (
StudentId int identity(1, 1),
StudentName nvarchar(255))
create table StudentGrades (
StudentId int,
SubjectId int,
GradeId int,
SemesterId int )
create FUNCTION [dbo].[fnArray] ( #Str varchar(max), #Delim varchar(1) = ' ', #RemoveDups bit = 0 )
returns #tmpTable table ( arrValue varchar(max))
as
begin
declare #pos integer
declare #lastpos integer
declare #arrdata varchar(8000)
declare #data varchar(max)
set #arrdata = replace(#Str,#Delim,'|')
set #arrdata = #arrdata + '|'
set #lastpos = 1
set #pos = 0
set #pos = charindex('|', #arrdata)
while #pos <= len(#arrdata) and #pos <> 0
begin
set #data = substring(#arrdata, #lastpos, (#pos - #lastpos))
if rtrim(ltrim(#data)) > ''
begin
if #RemoveDups = 0
begin
insert into #tmpTable ( arrValue ) values ( #data )
end
else
begin
if not exists( select top 1 arrValue from #tmpTable where arrValue = #data )
begin
insert into #tmpTable ( arrValue ) values ( #data )
end
end
end
set #lastpos = #pos + 1
set #pos = charindex('|', #arrdata, #lastpos)
end
return
end
select *
from Students st
inner join StudentGrades sg on sg.StudentId = st.StudentId
inner join Subject s on sg.SubjectId = s.SubjectId
inner join GradingScale gs on sg.GradeId = gs.GradeId
inner join dbo.fnArray(#subjects, ',') sArr on s.SubjectId = convert(int, sArr.arrValue)
inner join dbo.fnArray(#grades, ',') gArr on gs.GradeId = convert(int, gArr.arrValue)
obviously #subjectId and #gradeId could be passed in via some drop down selectors or however your UI is composed.
Edited to use dbo.fnArray, a little tool that can parse delimited strings into a list.
Now of course this would mean that if you had 2 subjects and 2 grades...like Show me all students that took ( Math and Science ) and scored ( 2 or 3 ) this would work. However if you wanted students who took Math and scored 2 or 3 or Students who took Science and scored a 3 you would have to rework the query.