What is the advantage of using @ParmDefinition in sp_executesql

Question

DECLARE @id int
DECLARE @name nvarchar(20)
SET @id = 5
SET @name = \'Paul\'

What is the difference between these two options:

Set @SQLQ         


        

Answer 1

I see no one mentioned one of most important things. When you're using parameterized query, your execution plans are cached.

Your query, which is:

SELECT *
FROM someTable
WHERE ID = @id
    AND NAME = @name;

Its execution plan will be stored im memory and it will be reused each time you query it (which is a great benefit). Meanwhile if you're generating your code using string concatenation like that:

Set @SQLQueryInnen = 'SELECT * FROM someTable WHERE ID = ' + @id + ' AND NAME = ''' + @name + ''''
Execute sp_Executesql @SQLQueryInnen

Your code will generate execution plan for each parameter combination (unless it's repeating) and cached plan will not be reused. Imagine that you're passing @Id = 1 and @Name = 'Paul', Your generated query will look like:

SELECT *
FROM someTable
WHERE ID = 5
    AND NAME = 'Paul';

If you change your name to 'Rob', your generated query will look like and SQL Server will have to create a new plan for it:

SELECT *
FROM someTable
WHERE ID = 5
    AND NAME = 'Rob';

Meaning plans won't be reused. Hope it helps.

This is an article explaing this in a bit more detail: EXEC vs. sp_executeSQL (Don't rely on article title, it explains exact differences you asked on your question). Quote from it:

The TSQL string is built only one time, after that every time same query is called with sp_executesql, SQL Server retrieves the query plan from cache and reuses it