Insufficient number of user-defined foreign tables

Query goal:

There must be at least n (two in this case) user-defined foreign tables 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 foreign tables (two 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

Data source:

INFORMATION_SCHEMA only

SQL query:

Click on query to copy it

WITH foreign_tables AS (SELECT foreign_table_schema, foreign_table_name
FROM information_schema.foreign_tables
WHERE foreign_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 foreign tables, must be at least one (two if you make your project based on the workbook)' As comment, (SELECT Count(*) AS cnt FROM foreign_tables) AS number_of_foreign_tables
WHERE (SELECT Count(*) AS cnt FROM foreign_tables)<2;

Collections where the query belongs to

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 .

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 .

Categories where the query belongs to

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.
Distributed database	Queries of this category provide information about the foreign table mechanism.

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.

Distributed database

Queries of this category provide information about the foreign table mechanism.