How to Extract Indexed Column Information in PostgreSQL?

Extracting Indexed Column Information in PostgreSQL

In PostgreSQL, obtaining the columns included in an index is a valuable task for database analysis and performance optimization. Unlike MySQL's SHOW INDEXES FOR command, PostgreSQL does not have a straightforward way to retrieve this information. However, by utilizing system tables and aggregate functions, it is possible to achieve similar results.

Retrieving Indexed Columns and Indices

The following query leverages the pg_class, pg_index, and pg_attribute system tables to gather details about indexes and their associated columns:

SELECT
    t.relname AS table_name,
    i.relname AS index_name,
    a.attname AS column_name
FROM
    pg_class t,
    pg_class i,
    pg_index ix,
    pg_attribute a
WHERE
    t.oid = ix.indrelid
    AND i.oid = ix.indexrelid
    AND a.attrelid = t.oid
    AND a.attnum = ANY(ix.indkey)
    AND t.relkind = 'r'
    AND t.relname LIKE 'table_name_pattern';

This query retrieves the table name, index name, and column names for all indexes on a specified table or a group of tables.

Grouping Indexed Columns

To obtain a consolidated list of columns indexed by each index, the query can be modified to group the results and aggregate the column names using the array_to_string() function:

SELECT
    t.relname AS table_name,
    i.relname AS index_name,
    array_to_string(array_agg(a.attname), ', ') AS column_names
FROM
    pg_class t,
    pg_class i,
    pg_index ix,
    pg_attribute a
WHERE
    t.oid = ix.indrelid
    AND i.oid = ix.indexrelid
    AND a.attrelid = t.oid
    AND a.attnum = ANY(ix.indkey)
    AND t.relkind = 'r'
    AND t.relname LIKE 'table_name_pattern'
GROUP BY
    t.relname,
    i.relname;

This query will provide a tabular output showing the table name, index name, and a comma-separated list of columns included in each index. This information can be valuable for understanding the indexing strategy and optimizing database performance.

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