Answer by Chase Seibert for Using ALTER to drop a column if it exists in MySQL

There is no language level support for this in MySQL. Here is a work-around involving MySQL information_schema meta-data in 5.0+, but it won't address your issue in 4.0.18.

drop procedure if exists schema_change;delimiter ';;'create procedure schema_change() begin    /* delete columns if they exist */    if exists (select * from information_schema.columns where table_schema = schema() and table_name = 'table1' and column_name = 'column1') then        alter table table1 drop column `column1`;    end if;    if exists (select * from information_schema.columns where table_schema = schema() and table_name = 'table1' and column_name = 'column2') then        alter table table1 drop column `column2`;    end if;    /* add columns */    alter table table1 add column `column1` varchar(255) NULL;    alter table table1 add column `column2` varchar(255) NULL;end;;delimiter ';'call schema_change();drop procedure if exists schema_change;

I wrote some more detailed information in a blog post.