Postgresql Crosstab Query

sql

crosstab

data-integrity

json-functions

byNikita Barsukov·Aug 4, 2024

To leverage PostgreSQL crosstab functionality, ensure the tablefunc extension is installed. Use the crosstab function as illustrated:

SELECT * FROM crosstab(
  $$SELECT row_label, category, value FROM your_table ORDER BY 1,2$$
) AS result(row_label data_type, category1 data_type, category2 data_type);

Take note that your ORDER BY outputs have to align with what crosstab anticipates. Adapt row_label, category, value, and data_type to fit your schema specifics.

Smoothing over the bumps

In cases of missing attributes or surplus rows in crosstab queries, resort to the safeguarded version of the crosstab function. Use category SQL and value SQL to specify category and value rows:

SELECT * FROM crosstab(
  $$SELECT row_label, category, value FROM your_table$$,
  $$SELECT DISTINCT category FROM your_table ORDER BY 1$$
) AS result(row_label data_type, category1 data_type, ...);

This usage ensures each expected output column is available, even in the absence of the corresponding input. It results in consistent and stable output.

Level-up with crosstab alternatives

If you wish to cater to a wide spectrum of data types, crosstab offers flexibility. Just remember to explicitly state type casts:

SELECT * FROM crosstab(
  $$SELECT row_label, category, value::text FROM your_table ORDER BY 1,2$$
) AS final_result(row_label data_type, category1 desired_data_type, ...);

Also, validate extension's availability in your PostgreSQL instance:

SELECT * FROM pg_proc WHERE proname = 'crosstab';

If crosstab played hard to get

In instances where tablefunc is elusive, lean to JSON functions or aggregation paired with CASE expressions:

SELECT 
  row_label,
  JSON_OBJECT_AGG(category, value) as categories
FROM your_table
GROUP BY row_label;

SELECT 
  row_label,
  SUM(case when category = 'category1' then value else 0 end) as category1,
  SUM(case when category = 'category2' then value else 0 end) as category2
FROM your_table
GROUP BY row_label;

Above alternatives mimic crosstab() to deliver a similar pivot table experience.

`\crosstabview`

For a more intuitive, client-side pivot table representation, use the \crosstabview meta-command. It's handy for ad-hoc queries in psql terminal.

Take care with duplicates

Prevent duplicates to ensure accurate crosstab output. Remember, duplicates in your data can lead to confusing results and jeopardize your data integrity.