Question

I’m using Postgresql and PHP 5.3.x with PDO to access the DB.

I have this the SQL query (stripped down version), with a placeholder for PDO to fill in:

INSERT INTO t_articles (a_article_id) VALUES (?) RETURNING a_id

I want a_article_id to be either a number, like 5, or else it should be the result of the subquery:

((SELECT max(a_article_id) FROM t_articles) + 1)

However, PDO says:

SQLSTATE[22P02]: Invalid text representation: 7 ERROR: invalid input syntax for integer: "(SELECT max(a_article_id) FROM t_articles) + 1"

And I’ve tried to set the subquery as the default value, but it is not allowed apparently:

ERROR:  cannot use sub query in default expression

How can I insert the result of this sub query (or what can be done to achieve the same result)?

Answer 1

You’d have to use INSERT…SELECT for that:

insert into t_articles (a_article_id)
select max(a_article_id) + 1
from t_articles
returning id

Or if you don’t need contiguous values for a_article_id, use a sequence for it:

1. Create a sequence, we’ll call it article_id_sequence.

   -- Get the current max(a_article_id)+1 to use instead of FIRST_VAL below
   create sequence article_id_sequence
   start FIRST_VAL
   owned by t_articles.a_article_id;
   

2. Set the default value for t_articles.a_article_id to nextval('article_id_sequence').

   alter table t_articles
   alter column a_article_id
   set default nextval('article_id_sequence');
   

3. Use the default value when inserting:

   insert into t_articles (a_article_id)
   values (default)
   returning id;