对于每个循环SQL

Question

Table1

id

Table2

id

Table3

id|table1_id|table2_id

I need the SQL (using MySQL) statement for:

for each row in table1 {
   for each row in table2 {
       insert in table3 values table1.id, table2.id;
}

Does an insert/select statement exists ? Or do I have to use a loop ?

Answer 1

You don't need to use loops at all. You should be thinking in terms of SETS when using a relational database.

Here is the correct way to achieve this. First using the CROSS JOIN to create a cartesian set of all the combinations of ids from table1 and table2. Then inserting that entire set into table3 Note: I am assuming Table3 ID is an auto-number.

INSERT INTO TABLE3 (TABLE1_ID,TABLE2_ID)
SELECT  T1.ID
        ,T2.ID
FROM    TABLE1 T1
CROSS JOIN
        TABLE2 T2