Dynamic SQL

Question

Dynamic SQL

astrid 69000

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Points: 3208
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June 15, 2016 at 2:26 am

#317278

Hi 🙂
I am trying to build a procedure that given a table name will do a select from that table. not only that i am having issues also that i read i need to be careful with SQL Injection and I also have no clue how to prevent that.
here are my sample tables
create table model1
(
id int,
mydata nvarchar (10)
)
insert into model1 (id, mydata) values (1, 'astrid');
insert into model1 (id, mydata) values (2, 'peter');
insert into model1 (id, mydata) values (3, 'netha');
select * from model1
create table model2
(
id int,
mydata nvarchar (10)
)
insert into model2 (id, mydata) values (1, 'astrid');
insert into model2 (id, mydata) values (2, 'peter');
insert into model2 (id, mydata) values (3, 'netha');
select * from model2
create table model3
(
id int,
mydata nvarchar (10)
)
insert into model3 (id, mydata) values (1, 'astrid');
insert into model3 (id, mydata) values (2, 'peter');
insert into model3 (id, mydata) values (3, 'netha');
select * from model3
and this is what i have so far but no no, doesnt want to work :crying:
create procedure DailyReport_sp
@ModelNumber nvarchar(100),
@debug bit = 0
as
Begin
declare @TableName nvarchar(200)
set @TableName = select name from sys.objects where type = 'u' and name = @ModelNumber
set @sqlquery = 'SELECT * FROM ' + @TableName
if @debug = 1 PRINT @sql
end

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Cadavre SSC-Forever Points: 41690 More actions · Answer 1

Your "PRINT" is printing a variable called "@sql", whilst your statement is being appended to a variable called "@SQLQuery".

This seems like an odd requirement, why do you want to do this?

Forever trying to learn
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BrainDonor SSCoach Points: 19254 More actions · Answer 2

Having set the value for @sqlquery you then need to execute it:

exec sp_executesql @sqlquery

Steve Hall
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astrid 69000 Hall of Fame Points: 3208 More actions · Answer 3

i just google it, and it doesn't work

so basically i am asking how to fix the procedure and prevent the sql injection.

thanks!!!

BrainDonor SSCoach Points: 19254 More actions · Answer 4

astrid 69000 (6/15/2016)
i just google it, and it doesn't work
so basically i am asking how to fix the procedure and prevent the sql injection.
thanks!!!

What error do you get that is telling you it won't work?

Steve Hall
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astrid 69000 Hall of Fame Points: 3208 More actions · Answer 5

this is the error i get

Msg 156, Level 15, State 1, Procedure general_select, Line 8

Incorrect syntax near the keyword 'select'.

Msg 137, Level 15, State 1, Procedure general_select, Line 9

Must declare the scalar variable "@SQLQuery".

Msg 137, Level 15, State 2, Procedure general_select, Line 10

Must declare the scalar variable "@sql".

but i also dont know if what i am doing is good or not, which is probably bad

BrainDonor SSCoach Points: 19254 More actions · Answer 6

have a look at the differences:

create procedure DailyReport_sp

@ModelNumber nvarchar(100),

@debug bit = 0

as

Begin

declare @TableName nvarchar(200), @sqlquery nvarchar(200)

select @TableName = name from sys.objects where type = 'u' and name = @ModelNumber

set @sqlquery = 'SELECT * FROM ' + @TableName

if @debug = 1 PRINT @sqlquery

exec sp_executesql @sqlquery

end

Steve Hall
Linkedin
Blog Site

astrid 69000 Hall of Fame Points: 3208 More actions · Answer 7

ohh... i didnt declare the one of the variables... shame on me :ermm:

that being said, thanks a bunch for the help 🙂

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 8

astrid 69000 (6/15/2016)
Hi 🙂
I am trying to build a procedure that given a table name will do a select from that table...

Just curious...since EXEC DailyReport_sp 'MyTablename' is exactly equivalent to SELECT * FROM MyTablename, what do you gain from this? What's the bigger picture?

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

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