Can I know if a database have DELETE ON CASCADE
with a query?
Yes. Just query the INFORMATION_SCHEMA
SELECT * FROM information_schema.REFERENTIAL_CONSTRAINTS
Or more specifically
-- 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
Read more about the REFERENTIAL_CONSTRAINTS
table in the manual