Question

I have a Conditions table that looks like this :

Conditions

• ConditionID
• MappingID
• VariableID
• CompareToVariableID
• ConditionOperator ( can be == or <> )
• ConjunctionOperator ( can be && or || )
• ConjunctionOrder

Now I have a SP that I want to implement these conditions on depending on MappingID.

If a MappingID is selected, all mapped conditions should be checked before anything happens in my SP.

SELECT * 
FROM Conditions
WHERE MappingID = @MappingID
ORDER BY ConjunctionOrder

For example if a certain MappingID had three rows in the Conditions table then :

IF VARIABLEID CONDITIONOPERATOR COMPARETOVARIABLEID CONJUNCTIONOPERATOR --row1
VARIABLEID CONDITIONOPERATOR COMPARETOVARIABLEID CONJUNCTIONOPERATOR  --row2
VARIABLEID CONDITIONOPERATOR COMPARETOVARIABLEID --row3 (ignore ConjunctionOperator for last row)
BEGIN
   --my code goes here
END
ELSE
BEGIN
   --my code here
END

I would like to know how I can implement the IF statement.

Answer 1

One way of doing it is like this (these are the steps in your stored procedure)

1. Take your conditions off the Conditons table and produce a special booolean expression out of it. You can do it by using a cursor over your SELECT query from your post. You should convert your variable IDs so that they won’t mix with the variable values (you’ll see later what I mean). Let’s suppose your query returned:

|-----------------------------------------------------------------------------------------|
|VariableID |COmpareToVariableID |ConditionOperator |ConjunctionOperator |ConjunctionOrder|
|-----------|--------------------|------------------|--------------------|----------------|
|A          |B                   |==                |&&                  |1               |
|C          |D                   |>> (NE)           |                    |2               |
|-----------|--------------------|------------------|--------------------|----------------|

Your expression (kept in a local SP variable) should be:

SELECT 1 WHERE #A# = #B# AND #C# >> #D#

In other words you add SELECT 1 WHERE at the beginning and relpace condition operator == with = and conjunction operator && with ‘AND’, and || with ‘OR’

1. Now you do a cursor query over your Variables table. In each loop you replace the names of the variables with its values (i.e. #A# is replaced with A value). At the end your expression should look like ‘SELECT 1 WHERE 1=2 AND 3<>3’.

2. You use sp_executesql to execute your dynamically created query. You can put the output in an OUTPUT parameter and check it in your IF statment in your SP.