Question

Given a table rules

rule_id = 1
rule_condition = 'size > 15'

how can I run a query like this

SELECT * FROM rawdata where (Select rule_condition FROM rules WHERE rule_id=1)

Is the only way to do it a stored procedure like this: mysql – query inside a query

Answer 1

This is essential reading for you before starting with dynamic SQL

For SQL Server you would use something like…

DECLARE @dynamicsql NVARCHAR(1000)

SELECT @dynamicsql =N'SELECT * FROM rawdata where ' + rule_condition 
FROM rules 
WHERE rule_id=1

IF(@@ROWCOUNT = 1)
   EXEC(@dynamicsql)

Hopefully you are not planning on allowing users to enter arbitrary rule_condition s as they could execute any arbitrary statements against your SQL Server.