If you watched Finding Poorly Designed Schemas and How to Fix Them you witnessed Marcos Albe use some very interesting queries. These queries let you find tables without primary keys, tables with non-integer primary keys, tables that do not use InnoDB, tables and indexes with the most latency, indexes that are 50% larger than the table, find duplicate indexes, and find unused indexes. As promised, they are below.
— Find tables without PK
SELECT t.table_schema,t.table_name,t.engine
FROM information_schema.tables t
JOIN information_schema.columns c
ON t.table_schema=c.table_schema
AND t.table_name=c.table_name
WHERE t.table_schema NOT IN (‘mysql’, ‘information_schema’,
‘sys’, ‘performance_schema’)
AND t.table_type = ‘BASE TABLE’
GROUP BY t.table_schema,t.table_name, t.engine
HAVING …