PostgreSQL 11 Administration Cookbook

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A very important pg_stat_statements feature is the normalization of queries that can be planned (SELECT, INSERT, DELETE, and UPDATE). You might have indeed noticed some ? characters in the query field being returned by the queries we outlined in the previous section. The normalization process intercepts constants in SQL statements run by users and replaces them with a placeholder (identified by a question mark).

Consider the following queries:

SELECT * FROM bands WHERE name = 'AC/DC';SELECT * FROM bands WHERE name = 'Lynyrd Skynyrd';

After the normalization process, these two queries appear as one in pg_stat_statements:

gabriele=# SELECT query, calls FROM pg_stat_statements;                 query                 | calls---------------------------------------+------- ...