Conversion of SQL Server stored procedure to a query

Question

I want to convert a stored procedure to a SQL query.

Here is the stored procedure in simple format:

SELECT
    table1.* 
INTO 
    #raw_data
FROM 
    table_1 WITH (NOLOCK)
WHERE 
    (a lot of conditions and filtering follows)

SELECT
    xyz,
    pqr,
    (SELECT (something)
     FROM #raw_data aa
     WHERE aa.id1 = a.id1
       AND aa.id2 = a.id2
       ...)
INTO 
    #temp_data
FROM 
    #raw_data a
JOIN 
    table_2 b WITH (NOLOCK) ON a.xid = b.xid

To convert this stored procedure into a SQL query, can I replace all the #raw_data in the second SELECT statement with:

SELECT table1.*
FROM table_1 WITH (NOLOCK)
WHERE (a lot of conditions and filtering follows)

I would like to know if there is a better way to do it.

Answer 1

So you turned it into...

SELECT xyz
, pqr
, (
    SELECT (something)
    FROM (
    SELECT table_1.*
        FROM table_1 WITH (NOLOCK)
        WHERE (a lot of conditions and filtering follows)
    ) aa
    WHERE aa.id1 = a.id1
    AND aa.id2 = a.id2
    ...
)

INTO #temp_data

FROM (
    SELECT table_1.*
    FROM table_1 WITH (NOLOCK)
    WHERE (a lot of conditions and filtering follows)
  ) a
  inner JOIN table_2 b WITH (NOLOCK) ON a.xid = b.xid

But you should keep going. The correlated subquery is not needed in this case. It doesn't appear to add any value. It makes the query more complicated. It also slows it down since the subquery must be run once for every row in the outer query. To take advantage of SQL Server's ability to join sets of data en masse...

SELECT xyz
, pqr
, aa.something

INTO #temp_data

FROM (
    SELECT table_1.*
    FROM table_1 WITH (NOLOCK)
    WHERE (a lot of conditions and filtering follows)
  ) a
  inner join (
    SELECT table_1.*
    FROM table_1 WITH (NOLOCK)
    WHERE (a lot of conditions and filtering follows)
  ) aa on aa.id1 = a.id1
      and aa.id2 = a.id2
      ...
  inner JOIN table_2 b WITH (NOLOCK) ON a.xid = b.xid

Assuming you're always joining table_1 to table_1 by using the same column on both sides of the join, as in your code) you may be able to simplify further. Be careful here. I assume that xid is unique or is included in the join between a and aa . If it is not, you'll want to stop here.

So, if you can simplify further, the next step is...

SELECT xyz
, pqr
, a.something

INTO #temp_data

FROM (
    SELECT table_1.*
    FROM table_1 WITH (NOLOCK)
    WHERE (a lot of conditions and filtering follows)
  ) a
  inner JOIN table_2 b WITH (NOLOCK) ON a.xid = b.xid

...and can be simplified to...

SELECT xyz
, pqr
, a.something

INTO #temp_data

FROM table_1 a WITH (NOLOCK)
  inner JOIN table_2 b WITH (NOLOCK) ON a.xid = b.xid

WHERE (a lot of conditions and filtering follows)

It looks like there may be considerably more complexity that you didn't share (the three dots of uncertainty).

WHERE aa.id1 = a.id1
  AND aa.id2 = a.id2
  ...

Your mileage may vary.