SQL : Running select statement for local string variable

Question

Here is a case where I am running SQL select statement on local string. If I run normal select query for my tables then it works.

select * from tablesname

But if I have following case :

declare @string nvarchar(400)

set @string = N'from tablesname'

Now if I run select * from @string , it is not working as expected.

Please suggest me for to resolve this problem, since I want to run the select statement in this way only. If I should try some other way, then suggest me that.

Thanks, Tausif.

It's better practice to make a stored procedure/tvf/whatever to select from each table, rather than one that selects from any (via a parameter and dynamic sql). I'm guessing that's what you're trying to achieve anyway... — Bridge
– Bridge, Commented Aug 16, 2012 at 7:33

fancyPants · Accepted Answer · 2012-08-16 07:50:08Z

1

Assuming you are using MySQL since your question is tagged with it, although this set @string = N'from tablesname' suggests, that you're using MS SQL Server or something:

SET @yourDynamicTablename = 'yourTable';
SET @sql = CONCAT('SELECT * FROM ', @yourDynamicTablename );
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

You might want to put that in a stored procedure.

Your attempt wasn't working, because you can't select from a string. For further reading about prepared statements, which are also useful for avoiding SQL injection attacks, have a look in the manual.

edited Aug 16, 2012 at 7:50

answered Aug 16, 2012 at 7:44

fancyPants

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