How to Create Crosstab Queries in PostgreSQL Using the tablefunc Extension?

Detailed explanation of PostgreSQL cross-table query: Use tablefunc extension to create pivot table

This article will introduce in detail how to use the tablefunc extension to create cross-table queries (Crosstab Queries) in PostgreSQL to implement pivot table conversion of data.

Create cross-table query

Cross-table query converts data into tabular format, where rows represent categories and columns represent values. PostgreSQL implements this functionality through the tablefunc extension.

Double parameter cross-table query syntax:

<code class="language-sql">SELECT *
FROM crosstab(
  'SELECT row_name, category, value
   FROM base_table
   ORDER BY 1, 2',
  'SELECT DISTINCT attribute FROM base_table ORDER BY 1',
) AS ct (row_name text, column_1 type_1, ..., column_n type_n);</code>

Handling missing attributes:

If there are missing attributes in the base table, you can use the second parameter to specify which attributes to include in the cross-table. The value of missing attributes will be empty.

Handle redundant input lines:

• Single parameter form: Extra lines will be discarded, older lines first.
• Two-argument form: Later lines will overwrite existing values ​​for the same category and attribute combination.

Advanced cross-table query:

• Multi-column pivot: Use multiple ORDER BY clauses in the first parameter query.
• Dynamic pivot alternative: Use the CASE and GROUP BY statements.

Use crosstabview in psql (PostgreSQL 9.6 and above):

Use the crosstabview meta command in psql to perform cross-table queries:

<code class="language-sql">\crosstabview</code>

Example query:

Consider the following example table:

<code class="language-sql">Section    Status    Count
A          Active    1
A          Inactive  2
B          Active    4
B          Inactive  5</code>

To create a cross-table with Section as row and Status as column:

<code class="language-sql">SELECT *
FROM crosstab(
  'SELECT section, status, COUNT(*) FROM tbl GROUP BY 1, 2',
  'SELECT DISTINCT status FROM tbl ORDER BY 1',
) AS ct (Section text, Active int, Inactive int);</code>

Result:

<code>Section    Active    Inactive
A          1         2
B          4         5</code>

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