Question: Unpreparing a statement after use

The documentation suggests calling ‘unprepare’ after you execute the prepared statement; but doing this removes the prepared statement from SQL Server thus negating the point of preparing it in the first place.

Preparing the statement, creates an execution plan for the query thus making future calls much quicker (3 to 4 times MS says) as it can reuse the plan; unpreparing it actually makes the query slower as it has to do more roundtrips than if you just called it as a normal query.

SQL Server Documentation https://docs.microsoft.com/en-us/sql/relational-databases/system-stored-procedures/sp-prepare-transact-sql?view=sql-server-2017

Is my understanding flawed?

-- Prepare query
DECLARE @P1 int;  
EXEC sp_prepare @P1 output,   
    N'@Param int',  
    N'SELECT *
FROM Sales.SalesOrderDetail AS sod
INNER JOIN Production.Product AS p ON sod.ProductID = p.ProductID
WHERE SalesOrderID = @Param
ORDER BY Style DESC;'; 

EXEC sp_execute 1, 49879;  
GO

EXEC sp_execute 1, 48766;
GO

EXEC sp_unprepare 1; 
GO

Software versions

• NodeJS: v10.15.0
• node-mssql: v4.3.0
• SQL Server: Microsoft SQL Server 2016 (SP1) - 13.0.4001.0 (X64)

[danpetitt]

Totally understood. Thx for the help

[dimisus]

I was also confused by the unprepare and I ended up using only prepare and execute… I just push different params inside the prepared query by using input … it brought me up to 5x performance.

Maybe it is a lack of knowledge but I think unprepare is in the docs to show it can be used, but is optional.