From: Todd Benson <caduceass@...>
Date: 2008-04-12T08:43:59+09:00
Subject: Re: How to check record duplication before saving?

On Fri, Apr 11, 2008 at 6:01 PM, Frank Tsao <shuhao.tsao@gmail.com> wrote:
> RubyTalk@gmail.com wrote:
>  > If you are using Rails and migrations
>  >
>  > add_index(:table, [:column1, :column2], :unique => true)
>  >
>  > if not something like this sql
>  >
>  >  CREATE UNIQUE INDEX index_name ON table(column1,column2);
>  >
>  > Becker
>
>  Thanks for your help, but the situation in A=1, B=2 or A=2, B=1 that
>  wont be accepted if using unique.
>
>  My point is that when record(A=1, B=1) was existed in database, any new
>  record(A=1, B=1) can not be valided. They can be (A=1, B=2), (A=1, B=3)
>  or (A=5, B=1) etc.

You probably have a primary key constraint on one of the columns
(unless you are using kindergarten SQLite).  Example without correct
caps...

create table stuff (
  colA int not null,
  colB int not null,
  primary key (colA, colB)
)

...or if you succumb to the idea integer IDs for the primary key are a
good idea...

create table stuff (
  id int not null primary key,
  colA int not null,
  colB int not null,
  unique (colA, colB)
)

Not tested.

Todd