Question

I am working on an application that has to assign numeric codes to elements. This codes are not consecutives and my idea is not to insert them in the data base until have the related element, but i would like to find, in a sql matter, the not assigned codes and i dont know how to do it.

Any ideas? Thanks!!!

Edit 1

The table can be so simple:

code | element  ----------------- 3    | three  7    | seven  2    | two 

And I would like something like this: 1, 4, 5, 6. Without any other table.

Edit 2

Thanks for the feedback, your answers have been very helpful.

Answer 1

This will return NULL if a code is not assigned:

SELECT  assigned_codes.code FROM    codes  LEFT JOIN         assigned_codes ON      assigned_codes.code = codes.code WHERE   codes.code = @code 

This will return all non-assigned codes:

SELECT  codes.code FROM    codes  LEFT JOIN         assigned_codes ON      assigned_codes.code = codes.code WHERE   assigned_codes.code IS NULL 

There is no pure SQL way to do exactly the thing you want.

In Oracle, you can do the following:

SELECT  lvl FROM    (         SELECT  level AS lvl         FROM    dual         CONNECT BY                 level <=                 (                 SELECT  MAX(code)                 FROM    elements                 )         ) LEFT OUTER JOIN         elements ON      code = lvl WHERE   code IS NULL 

In PostgreSQL, you can do the following:

SELECT  lvl FROM    generate_series(         1,         (         SELECT  MAX(code)         FROM    elements         )) lvl LEFT OUTER JOIN         elements ON      code = lvl WHERE   code IS NULL