Sprawdź, czy tabela ma DELETE na CASCADE

Question

Czy mogę wiedzieć, czy baza danych ma DELETE ON CASCADE z zapytaniem?

Answer 1

Można użyć

SHOW CREATE TABLE `tablename` 

Aby uzyskać całą definicję tabeli. Obejmuje to wszelkie ograniczenia klucza obcego.

Answer 2

Tak. Wystarczy kwerendy INFORMATION_SCHEMA

SELECT * FROM information_schema.REFERENTIAL_CONSTRAINTS 

a dokładniej

-- This query will list all constraints, their delete rule, 
-- the constraint table/column list, and the referenced table 
SELECT 
    r.CONSTRAINT_NAME, 
    r.DELETE_RULE, 
    r.TABLE_NAME, 
    GROUP_CONCAT(k.COLUMN_NAME SEPARATOR ', ') AS `constraint columns`, 
    r.REFERENCED_TABLE_NAME 
FROM information_schema.REFERENTIAL_CONSTRAINTS r 
    JOIN information_schema.KEY_COLUMN_USAGE k 
    USING (CONSTRAINT_CATALOG, CONSTRAINT_SCHEMA, CONSTRAINT_NAME) 
-- using MySQL's GROUP BY clause. In other DB's more columns would need to be 
-- specified! 
GROUP BY r.CONSTRAINT_CATALOG, 
     r.CONSTRAINT_SCHEMA, 
     r.CONSTRAINT_NAME 

Czytaj więcej o REFERENTIAL_CONSTRAINTS table in the manual