[10.x] allow insert..select (insertUsing()) to have empty $columns

[jonnott]

Enables queries which insert all columns from the source table into the destination table, e.g. "insert into users select * from users”, when the table schemas exactly match.

(alter testPreservedAreAppliedByInsertUsing() to not conflict with new behaviour)

[taylorotwell]

I wonder if we should add a new helper method for this so you don't have to pass an empty array?

[taylorotwell]

Updated to also allow ['*'] for columns.

[jonnott]

I wonder if we should add a new helper method for this so you don't have to pass an empty array?

@taylorotwell Aha, I see the genius of your addition .. as you can't specify * for the INSERT part of an INSERT..SELECT because MySQL (at least) doesn't like it..

e.g. insert into users_archive (*) select * from users will result in:

Query 1 ERROR: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '*) select * from users' at line 1

..you've made it also omit the columns part if $columns is ['*'], therefore making it more developer-friendly, whilst also avoiding the syntax error.

Good job!