Reduce dynamic SQL using CASE to use “IN” or not

Question

I am converting a stored procedure which I had previously written as a string then, using BIT parameters I decided whether to append certain WHERE/ON clauses

This sp is passed a number of comma-separated strings and then some of the dynamic WHERE clauses are like:

IF @pUse_Clause_A THEN SET @WhereClause = @WhereClause + ' AND [FIELD_A] IN (' + @pComma_Separated_List_A + ')'

In this case, @pComma_Separated_List_A is something like '1,3,6,66,22' ... a list of the things I want included.

Now I am changing these from strings into TVP,s so I can just use "real" SQL like AND [FIELD_A] IN (SELECT [TVP_FIELD] FROM @pTVP_A)

When I do this, I don't like the string-building method

However, I also don't like having to nest the IF statements.

IF A 
    ENTIRE SQL WHERE A
ELSE
    ENTIRE SQL WITHOUT WHERE CLAUSE

The more parameters I add, the more complicated it gets:

IF A
    IF B
        SQL WHERE A AND B
    ELSE
        SQL WHERE A
ELSE
    IF B
        SQL WHERE B
    ELSE
        SQL

What I would rather do is something like this:

SELECT * FROM TABLE
WHERE 1=1
CASE USE_A WHEN 1 THEN 
     AND [FIELD_A] IN (SELECT A FROM TBP_A)
END
CASE USE_B WHEN 1 THEN
     AND [FIELD_B] IN (SELECT B FROM TVP_B)
END

I know it ignored SQL outside the chosen "IF" result, but having all that duplicated statement seems sloppy

Answer 1

Dynamically changing searches based on the given parameters is a complicated subject and doing it one way over another, even with only a very slight difference, can have massive performance implications. The key is to use an index, ignore compact code, ignore worrying about repeating code, you must make a good query execution plan (use an index).

Read this and consider all the methods. Your best method will depend on your parameters, your data, your schema, and your actual usage:

Dynamic Search Conditions in T-SQL by by Erland Sommarskog

The Curse and Blessings of Dynamic SQL by Erland Sommarskog