Posted on Thursday 2nd January 2020
I recently had to work on converting a copy of a large mysql database into a smaller development database. One of the early problems I had was one table had over 2 million rows, and I only needed a handful for testing. The easiest way i found to do this task was to create a new table with just the records I needed. Then swap them around.
MySQL has the nice option of creating a table directly from a select, such as the following:
create table new_table select * from old_table;
An example of this in action would be a booking system, where you only wanted to keep bookings from 2019.
create table bookings_2019; select * from bookings WHERE date >= '2019-01-01' and date < '2020-01-01';
In my instance I only would want the new records, so can drop the old data
DROP TABLE bookings; ALTER TABLE `bookings_2019` RENAME TO `bookings`;