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I am working on a function that allows me to add an index if it does not exist. I am running into the problem that I cannot get a list of indexes to compare to. Any thoughts?

This is a similar issue to the column creation one that is solved with this code:
http://stackoverflow.com/a/12603892/368511

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Have you looked at the PostgreSQL documentation at postgresql.org/docs/current/static/catalog-pg-index.html ? You can most likely run a query that will tell you if the index you want is already created. –  Max Vernon Feb 27 '13 at 21:26
1  
Goes without saying that you need to state your version of PostgreSQL for a question like that. –  Erwin Brandstetter Feb 27 '13 at 22:07
    
This is a good question, I am working in 8.4 in my production –  GuidoS Feb 28 '13 at 17:03

1 Answer 1

up vote 16 down vote accepted

Index names in PostgreSQL

  • Index names are unique across a single database schema.
  • Index names cannot be the same as any other table, view, sequence, user-defined composite type or index in the same schema.
  • Two tables in the same schema cannot have an index of the same name. (Follows logically.)

If you do not care about the name of the index, you can have Postgres auto-name it:

CREATE INDEX ON tbl1 (col1)

is (almost) the same as

CREATE INDEX tbl1_col1_idx ON tbl1 USING btree (col1);

Except that Postgres will avoid a naming collision and automatically pick the next free name:

tbl1_col1_idx 
tbl1_col1_idx2
tbl1_col1_idx3
...

Just try it. But obviously you would not want to create multiple redundant indexes. So it wouldn't be a good idea to just blindly create a new one.

Test for existence

A very simple way to test is to cast the schema-qualified name to regclass:

SELECT 'myschema.myname'::regclass

If it throws an exception, the name is free.
Or, to test the same without throwing an exception, used in a DO statement:

DO $$
BEGIN

IF NOT EXISTS (
    SELECT 1
    FROM   pg_class c
    JOIN   pg_namespace n ON n.oid = c.relnamespace
    WHERE  c.relname = 'my_name'
    AND    n.nspname = 'myschema' -- 'public' by default
    ) THEN

    CREATE INDEX my_name ON myschema.mytable (mycolumn);
END IF;

END$$;

The DO statement was introduced with Postgres 9.0. In earlier versions you have to create a function to do the same.
Details about pg_class in the manual.
Basics about indexes in the manual.

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So does this mean that index names are unique through an instance, not by table? –  GuidoS Feb 28 '13 at 13:41
    
ok, I see now that it's an issue of name spaces, so indexes are unique to the namespace/schema... thanks –  GuidoS Feb 28 '13 at 17:02
    
@GuidoS: I added a bit more to clarify that. –  Erwin Brandstetter Feb 28 '13 at 17:13

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