Unable to use crosstab in Postgres

Question

Postgres 9.2.1 on OSX 10.9.2.

If I run the following crosstab example query:

CREATE EXTENSION tablefunc; 

CREATE TABLE ct(id SERIAL, rowid TEXT, attribute TEXT, value TEXT);
INSERT INTO ct(rowid, attribute, value) VALUES('test1','att1','val1');

SELECT *
FROM crosstab(
  'select rowid, attribute, value
   from ct
   where attribute = ''att2'' or attribute = ''att3''
   order by 1,2')
AS ct(row_name text, category_1 text, category_2 text, category_3 text);

I get: ERROR: extension "tablefunc" already exists

But if I comment out CREATE EXTENSION

I get: ERROR: function crosstab(unknown) does not exist

How can I get out of this vicious circle? Is it a known issue?

Humpy

Answer 1

You can change the first line into:

CREATE EXTENSION IF NOT EXISTS tablefunc;

Camargo

Also make sure you are connected to the exact database when doing this. Otherwise it will still not work – Aspen

Answer 2

the problem in my case was that the 'tablefunc' extension was defined on one specific schema in my DB, and not accessible to all schemas in it.

[edit: as explained above, 'not accessible to all schemas' should read 'cannot be loaded on all schemas']

I learned that:

1. the Extension can only be loaded into one schema - so load it into 'public'
2. you have to manually drop the extension from one schema before you can load it in another
3. you can list the loaded extensions per schema in pqsl using the command: \df *.crosstab

[edit: 4. you can access the extension either by search_path, by loading it on public schema or by explicitly specifying a schema]

Humpy

Note that the public schema is just another schema. Needs to be in the search_path just like any other if you want to access it by default. – Ledford

Answer 3

There's a misconception in your answer:

and not accessible to all schemas in it.

All schemas inside the same database are accessible to all sessions in that same database, (as long as privileges are given). It's a matter of setting the search_path. Schemas work much like directories / folders in the file system.

Alternatively, you can schema-qualify the function (and even operators) to access it independently of the search_path:

SELECT *
FROM my_extension_schema.crosstab(
    $$select rowid, attribute, "value"
      from   ct
      where  attribute IN ('att2', 'att3')
      order  by 1,2$$
   ,$$VALUES ('att2'), ('att3')$$
   ) AS ct(row_name text, category_2 text, category_3 text);

More:

• How to use % operator from the extension pg_trgm?

Dubious crosstab()

Your query returned attributes 'att2' and 'att3', but the column definition list had three categories (category_1, category_2, category_3) that do not match the query.
I removed category_1 and added the second parameter to crosstab() - the "safe" version. More details here:

• PostgreSQL Crosstab Query

Aside:
Don't use value as column name, even if Postgres allows it. It's a reserved word in standard SQL.

Ledford

the (erroneous?) query came straight from the Docs postgresql.org/docs/9.1/static/tablefunc.html – Humpy

@Francis: Well, that example tries to demonstrates a shortcoming of the crosstab() function with one parameter. As you can see in the result there att2 ends up in category1, att3 in category2 and category3 remains empty. Probably not what one would normally intend ... – Ledford

fair enough. I was only using it to illustrate the curious absence of the tablefunc extension – Humpy