Postgres pivot table with crosstab - sql

Question

I have a table like the next one:
+------------+---------+---------+---------+
| date | value 1 | value 2 | value 3 |
+------------+---------+---------+---------+
| 01/01/2017 | 263 | 7 | 222 |
| 02/01/2017 | 275 | -9 | 209 |
| 03/01/2017 | 331 | -9 | 243 |
| . | . | . | . |
| . | . | . | . |
| . | . | . | . |
+------------+---------+---------+---------+
I want to create this other one in postgres:
+---------+---------------+------------+------------+
| | 01/01/2017 | 02/01/2017 | 03/01/2017 |
+---------+---------------+------------+------------+
| value 1 | 263 | 275 | 331 |
| value 2 | 7 | -9 | -9 |
| value 3 | 222 | 209 | 243 |
+---------+---------------+------------+------------+
But my problem is that I dont know how many dates I will have, so I have to use something like this:
SELECT * FROM crosstab(
$$ SELECT value1, date FROM myTable ORDER BY 1 $$,
$$ SELECT m FROM generate_series((select min(date) from myTable) ,(select max(date) from myTable), '1 month'::interval) m $$
) AS (
".." date, ".." date, ".." date, ".." date
);
Does someone can help me? Thanks.

Answer 1

Your basic issue is that PostgreSQL needs to know what the columns look like in order to plan the query. Consequently you need to return some sort of fixed-column structure. There are a number of ways you can do this:
Query dates first or allow them to be input, and then generate your query in the db client.
Wrap this in a stored procedure which returns a refcursor
Wrap in a stored procedure which returns a list of JSON representations of rows.
But either way you cannot do it in a query without dynamically generating the query somewhere.