There must be at least n (seven in this case) user-defined base tables in the database.
Notes
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 base tables (seven in this case) serves here as an example. It could be replaced with some other threshold.
Type
Problem detection (Each row in the result could represent a flaw in the design)
WITH tables AS (SELECT tables.table_schema, tables.table_name
FROM information_schema.tables
WHERE tables.table_type IN ('BASE TABLE') 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 base tables, must be at least seven' As comment, (SELECT Count(*) AS cnt FROM tables) AS the_number_of_tables
WHERE (SELECT Count(*) AS cnt FROM tables)<7;
Collections
This query belongs to the following collections:
Name
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 .
Categories
This query is classified under the following categories:
Name
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.