Adding, changing and removing columns.
WHEN YOU WOULD
Adding a column for custom data Widening a column that is rejecting values Adding an index Correcting a type
For application tables, prefer the application's own mechanism. Changing structure by hand puts you out of step with what the code expects.
IN PHPMYADMIN
The Structure tab lists columns with options to edit, drop and add.
BACK UP FIRST
Structure changes on a large table rewrite it, take time, and lock it while running.
On a busy site, do this at a quiet hour.
WIDENING A COLUMN
Safe. Existing data is preserved.
NARROWING ONE
Dangerous. Values longer than the new limit are truncated or rejected.
CHANGING A TYPE
Converting text to a number, or similar, can lose or mangle data. Test on a copy first.
DROPPING A COLUMN
Permanent. The data is gone.
FOR FRAMEWORK APPLICATIONS
Use migrations. Changing the database by hand means the next deployment disagrees with it.
