Question

I want to delete many rows with the same set of field values in some (6) tables. I could do this by deleting the result of one subquery in every table (Solution 1), which would be redundant, because the subquery would be the same every time; so I want to store the result of the subquery in a temporary table and delete the value of each row (of the temp table) in the tables (Solution 2). Which solution is the better one?

First solution:

DELETE FROM dbo.SubProtocols
WHERE ProtocolID IN (
    SELECT ProtocolID
    FROM dbo.Protocols
    WHERE WorkplaceID = @WorkplaceID
)

DELETE FROM dbo.ProtocolHeaders
WHERE ProtocolID IN (
    SELECT ProtocolID
    FROM dbo.Protocols
    WHERE WorkplaceID = @WorkplaceID
)

// ...

DELETE FROM dbo.Protocols
WHERE WorkplaceID = @WorkplaceID

Second Solution:

DECLARE @Protocols table(ProtocolID int NOT NULL)

INSERT INTO @Protocols
SELECT ProtocolID
FROM dbo.Protocols
WHERE WorkplaceID = @WorkplaceID

DELETE FROM dbo.SubProtocols
WHERE ProtocolID IN (
    SELECT ProtocolID
    FROM @Protocols
)

DELETE FROM dbo.ProtocolHeaders
WHERE ProtocolID IN (
    SELECT ProtocolID
    FROM @Protocols
)

// ...

DELETE FROM dbo.Protocols
WHERE WorkplaceID = @WorkplaceID

Is it possible to do solution 2 without the subquery? Say doing WHERE ProtocolID IN @Protocols (but syntactically correct)?

I am using Microsoft SQL Server 2005.

Answer 1

While you can avoid the subquery in SQL Server with a join, like so:

delete from sp
from subprotocols sp
inner join protocols p on
    sp.protocolid = p.protocolid
    and p.workspaceid = @workspaceid

You’ll find that this doesn’t gain you really any performance over either of your approaches. Generally, with your subquery, SQL Server 2005 optimizes that in into an inner join, since it doesn’t rely on each row. Also, SQL Server will probably cache the subquery in your case, so shoving it into a temp table is most likely unnecessary.

The first way, though, would be susceptible to changes in Protocols during the transactions, where the second one wouldn’t. Just something to think about.