SQL add new columns ignoring duplicates

Question

We have quite a few databases, and we're trying to run upgrade scripts on all of them to bring them up to date - as such, they all have different columns and tables.

We want to add new tables and columns if they arent already present, so for instance

CREATE TABLE IF NOT EXISTS `orders` ( `id` INT (11) NOT NULL , 
    `value` VARCHAR (50) , `designId` INT (11) , PRIMARY KEY ( `id`)); 

That works, but we're looking for the same kind of solution for columns. Our current solution throws Error Code: 1060 - Duplicate column name.

ALTER TABLE `orders` ADD COLUMN `customer` INT (1) NULL; 

I've tried the following from garry passarella, but i get an error claiming incorrect sql syntax:

IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS 
    WHERE TABLE_NAME = 'orders' AND COLUMN_NAME = 'customer') 
    BEGIN  ALTER TABLE orders
    ADD customer BIT DEFAULT NULL
END

If there is something we can use to get each line to ignore duplicates, or get the entire script to ignore error code 1060, it would be much appreciated.

Answer 1

The if ... begin ... end is SQL Server syntax. For MySQL, it's more like if ... then ... end if:

if not exists (select * from information_schema.columns
    where column_name = 'customer' and table_name = 'orders') then
    alter table orders add customer int(1) null;
end if

In reply to your comment: in MySQL, you can't type compound statements at the command line. They have to be in a function or stored procedure. For example:

drop procedure if exists sp_addcolumn;

delimiter //
create procedure sp_addcolumn()
begin
  if not exists (select * from INFORMATION_SCHEMA.COLUMNS 
      where table_name = 'orders' and column_name = 'customer') then
    alter table `orders` add column `customer` int(1) null;
  end if;
end//

delimiter ;
call sp_addcolumn;

There is an open request on the MySQL bug tracker to allow if statements outside stored procedures. It's current status is Needs Triage.