| Query goal: | There must be at least n (four in this case) user-defined views in the database. |
| Notes about the query: | This query implements a requirement that might occur in a learning situation. The condition in the query ensures that if the requirement is not fulfilled, then the query returns one row, otherwise it does not return a row. The result is achieved by using a PostgreSQL feature that permits SELECT statements without the FROM clause. The number of views (four in this case) serves here as an example. It could be replaced with some other threshold. |
| Query type: | Problem detection (Each row in the result could represent a flaw in the design) |
| Query reliability: | High (Few or no false-positive results) |
| Query license: | MIT License |
| Fixing suggestion: | Create additional views. |
| Data source: | INFORMATION_SCHEMA only |
| SQL query: | Click on query to copy it
WITH views AS (SELECT tables.table_schema, tables.table_name FROM information_schema.tables WHERE tables.table_type IN ('VIEW') AND 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)) SELECT 'Too few views, must be at least four' As comment, (SELECT Count(*) AS cnt FROM views) AS number_of_views WHERE (SELECT Count(*) AS cnt FROM views)<4; |
| Collection name | Collection description |
|---|---|
| Find problems automatically | Queries, that results point to problems in the database. Each query in the collection produces an initial assessment. However, a human reviewer has the final say as to whether there is a problem or not . |
| Category name | Category description |
|---|---|
| Assessment | Queries of this category could be used specifically in the learning environment to assess as to whether student projects have filled certain criteria. |
| Derived tables | Queries of this category provide information about the derived tables (views, materialized views), which are used to implement virtual data layer. |