


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:
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);
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
andGROUP BY
statements.
Use crosstabview
in psql (PostgreSQL 9.6 and above):
Use the crosstabview
meta command in psql to perform cross-table queries:
\crosstabview
Example query:
Consider the following example table:
Section Status Count A Active 1 A Inactive 2 B Active 4 B Inactive 5
To create a cross-table with Section as row and Status as column:
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);
Result:
<code>Section Active Inactive A 1 2 B 4 5</code>
The above is the detailed content of How to Create Crosstab Queries in PostgreSQL Using the tablefunc Extension?. For more information, please follow other related articles on the PHP Chinese website!

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