Get definition of function, sequence, type etc. in Postgresql with SQL query

To get the definition of a function use pg_get_functiondef():

select pg_get_functiondef(oid)from pg_procwhere proname = 'foo';

There are similar functions to retrieve the definition of an index, a view, a rule and so on. For details see the manual: http://www.postgresql.org/docs/current/static/functions-info.html

Getting the definition of a user type is a bit more tricky. You will need to query information_schema.attributes for that:

select attribute_name, data_typefrom information_schema.attributeswhere udt_schema = 'public'  and udt_name = 'footype'order by ordinal_position;

From that you need to re-assemble the create type statement.

For more details you will need to read through the documentation of the system catalog: http://www.postgresql.org/docs/current/static/catalogs.html

But you should prefer information_schema views if they return the same information.

You will find psql -E instrumental in your quest for those queries.
It displays the queries psql uses when executing its backslash-commands - like \df+ myfunc for details about this function.

Here is a complete sample query using pg_get_functiondef:

WITH funcs AS (  SELECT    n.nspname AS schema    ,proname AS sproc_name    ,proargnames AS arg_names    ,t.typname AS return_type    ,d.description    ,pg_get_functiondef(p.oid) as definition  FROM pg_proc p    JOIN pg_type t on p.prorettype = t.oid    JOIN pg_description d on p.oid = d.objoid    JOIN pg_namespace n on n.oid = p.pronamespace  WHERE n.nspname = 'some_schema_name_here')SELECT *FROM funcs;;

Note, you should obviously specify the schema name, (or "public" if you are using that schema)