| Query goal: | Find derived tables (views and materialized views) that sort rows based on random values. This can be used to find a random subset of rows. It is a computationally expensive operation. |
| Notes about the query: | In the returned subquery of view/materialized view the query replaces each newline character with the line break (br) tag for the better readability in case the query result is displayed in a web browser. |
| Query type: | Problem detection (Each row in the result could represent a flaw in the design) |
| Query reliability: | Medium (Medium number of false-positive results) |
| Query license: | MIT License |
| Fixing suggestion: | Bill Karwin in his book of SQL database design antipatterns offers various alternatives for finding a random subset of rows. |
| Data source: | INFORMATION_SCHEMA+system catalog |
| SQL query: | Click on query to copy it
SELECT table_schema, table_name, type, regexp_replace(view_definition,'[\r\n]','<br>','g') AS view_definition FROM (SELECT views.table_schema, views.table_name, 'VIEW' AS type, views.view_definition FROM information_schema.views WHERE table_schema NOT IN (SELECT schema_name FROM INFORMATION_SCHEMA.schemata WHERE schema_name<>'public' AND schema_owner='postgres' AND schema_name IS NOT NULL) UNION SELECT schemaname, matviewname, 'MATERIALIZED VIEW' AS type, regexp_replace(definition,'[\r\n]','<br>','g') AS definition FROM pg_catalog.pg_matviews) AS foo WHERE view_definition ~*'order[[:space:]]+by[[:space:]]+[(]random[(][)][)]' ORDER BY table_schema, table_name; |
| Category name | Category description |
|---|---|
| Derived tables | Queries of this category provide information about the derived tables (views, materialized views), which are used to implement virtual data layer. |
| Performance | Queries of this category provide information about indexes in a database. |
| Reference |
|---|
| This is one of the antipatterns from the Bill Karwin's book of SQL antipatterns. See Chapter 16: Random Selection. |