Postgresql crosstab query with multiple "row name" columns - postgresql

Question

I have a table that is a "tall skinny" fact table:
CREATE TABLE facts(
eff_date timestamp NOT NULL,
update_date timestamp NOT NULL,
symbol_id int4 NOT NULL,
data_type_id int4 NOT NULL,
source_id char(3) NOT NULL,
fact decimal
/* Keys */
CONSTRAINT fact_pk
PRIMARY KEY (source_id, symbol_id, data_type_id, eff_date),
)
I'd like to "pivot" this for a report, so the header looks like this:
eff_date, symbol_id, source_id, datatypeValue1, ... DatatypeValueN
I.e., I'd like a row for each unique combination of eff_date, symbol_id, and source_id.
However, the postgresql crosstab() function only allow on key column.
Any ideas?

Answer 1

crosstab() expects the following columns from its input query (1st parameter), in this order:
a row_name
(optional) extra columns
a category (matching values in 2nd crosstab parameter)
a value
You don't have a row_name. Add a surrogate row_name with the window function dense_rank().
Your question leaves room for interpretation. Let's add sample rows for demonstration:
INSERT INTO facts (eff_date, update_date, symbol_id, data_type_id, source_id)
VALUES
(now(), now(), 1, 5, 'foo')
, (now(), now(), 1, 6, 'foo')
, (now(), now(), 1, 7, 'foo')
, (now(), now(), 1, 6, 'bar')
, (now(), now(), 1, 7, 'bar')
, (now(), now(), 1, 23, 'bar')
, (now(), now(), 1, 5, 'baz')
, (now(), now(), 1, 23, 'baz'); -- only two rows for 'baz'
Interpretation #1: first N values
You want to list the first N values of data_type_id (the smallest, if there are more) for each distinct (source_id, symbol_id, eff_date).
For this, you also need a synthetic category, can be synthesized with row_number(). The basic query to produce input to crosstab():
SELECT dense_rank() OVER (ORDER BY eff_date, symbol_id, source_id)::int AS row_name
, eff_date, symbol_id, source_id -- extra columns
, row_number() OVER (PARTITION BY eff_date, symbol_id, source_id
ORDER BY data_type_id)::int AS category
, data_type_id AS value
FROM facts
ORDER BY row_name, category;
Crosstab query:
SELECT *
FROM crosstab(
'SELECT dense_rank() OVER (ORDER BY eff_date, symbol_id, source_id)::int AS row_name
, eff_date, symbol_id, source_id -- extra columns
, row_number() OVER (PARTITION BY eff_date, symbol_id, source_id
ORDER BY data_type_id)::int AS category
, data_type_id AS value
FROM facts
ORDER BY row_name, category'
, 'VALUES (1), (2), (3)'
) AS (row_name int, eff_date timestamp, symbol_id int, source_id char(3)
, datatype_1 int, datatype_2 int, datatype_3 int);
Results:
row_name | eff_date | symbol_id | source_id | datatype_1 | datatype_2 | datatype_3
-------: | :--------------| --------: | :-------- | ---------: | ---------: | ---------:
1 | 2017-04-10 ... | 1 | bar | 6 | 7 | 23
2 | 2017-04-10 ... | 1 | baz | 5 | 23 | null
3 | 2017-04-10 ... | 1 | foo | 5 | 6 | 7
Interpretation #2: actual values in column names
You want to append actual values of data_type_id to the column names datatypeValue1, ... DatatypeValueN. One ore more of these:
SELECT DISTINCT data_type_id FROM facts ORDER BY 1;
5, 6, 7, 23 in the example. Then actual display values can be just boolean (or the redundant value?). Basic query:
SELECT dense_rank() OVER (ORDER BY eff_date, symbol_id, source_id)::int AS row_name
, eff_date, symbol_id, source_id -- extra columns
, data_type_id AS category
, TRUE AS value
FROM facts
ORDER BY row_name, category;
Crosstab query:
SELECT *
FROM crosstab(
'SELECT dense_rank() OVER (ORDER BY eff_date, symbol_id, source_id)::int AS row_name
, eff_date, symbol_id, source_id -- extra columns
, data_type_id AS category
, TRUE AS value
FROM facts
ORDER BY row_name, category'
, 'VALUES (5), (6), (7), (23)' -- actual values
) AS (row_name int, eff_date timestamp, symbol_id int, source_id char(3)
, datatype_5 bool, datatype_6 bool, datatype_7 bool, datatype_23 bool);
Result:
eff_date | symbol_id | source_id | datatype_5 | datatype_6 | datatype_7 | datatype_23
:--------------| --------: | :-------- | :--------- | :--------- | :--------- | :----------
2017-04-10 ... | 1 | bar | null | t | t | t
2017-04-10 ... | 1 | baz | t | null | null | t
2017-04-10 ... | 1 | foo | t | t | t | null
dbfiddle here
Related:
Crosstab function in Postgres returning a one row output when I expect multiple rows
Dynamic alternative to pivot with CASE and GROUP BY
Postgres - Transpose Rows to Columns