"UPDATE table_name SET w = $1, x = $2, z = $4 WHERE y = $3 RETURNING *",
does not do the same as
"UPDATE table_name SET w = $1, x = $2, y = $3, z = $4 RETURNING *",
It's 2 am and my mind blanked out the WHERE, and just wanted the numbers neatly in order of 1234.
idiot.
FML.
mind explaining?
By running a select query first, you get a nice list of the rows you are going to change. If the list is the entire set, you'll likely notice.
If it looks good, you run the update query using the same where clause.
But that's for manual changes. OP's update statement looks like it might be generated from code, in which case this wouldn't have helped.