Multiple select for single row insert
This is typically achieved by writing a SELECT statement that outputs the fields in the same order as the INSERT statement and using that instead of a VALUES clause. For example, one might:

INSERT INTO my_table (field1, field2)
SELECT t1.field1, max(t2.field2)
FROM t1 INNER JOIN t2 ON (...)
GROUP BY t1.field1
WHERE something_else = 'whatever';


The point is that you can just do an

INSERT INTO ... SELECT ...


to insert rows. You do not have to create a VALUES clause and mess with subqueries.