FROM内部的SQL SELECT语句，带有INNER JOIN

Question

I am writing a stored procedure, inside of which I have some variables and a temp table.

I am trying to do the following:

INSERT INTO table1(
    col1,
    col2,
    col3,
SELECT
    @col1,
    t2.col2,
    t3.col3
FROM
    #table2 t2, 
         (SELECT * 
          FROM table4 t4 
          INNER JOIN #table2 t2 ON t4.ID = t2.ID) t3

However, say t2 and t3 have 5 rows, the above is inserting 5*5=25 rows, where it should just be 5. It seems like a cross product is being computed in the FROM between t2 and t3 , and I can't quite nail down why.

Answer 1

Are you sure you should be using a comma instead of an actual join there? That's probably what's causing a cross-product rather than a selection from joined rows.

Answer 2

Is this what you intend to do?

INSERT INTO table1(col1, col2, col3)
    SELECT @col1, t2.col2, t3.col3
    FROM table4 t4 INNER JOIN
         #table2 t2
         ON t4.ID = t2.ID;

Your original query has an extra reference to #table2 .