根据MySQL语句中的另一个表列动态确定列值

Question

Is there a way to perform a query in MySQL like this one in pseudo code:

INSERT INTO table_a(a, b, c) SELECT table_b.a, table_b.b, IF (table_b.c <100) 500 else 1000 WHERE ...

I know I can make two separate queries as a transaction but I want to know if there's a way to insert a value for a column based on another column from another table without going over the records twice.

Answer 1

Yes, there is. You can use the CASE construct:

INSERT INTO table_a (a, b, c) 
SELECT table_b.a, table_b.b, CASE WHEN table_b.c < 100 THEN 500 else 1000 END
FROM   table_b
WHERE  ...