Check out example codes for "find largest table in mysql database". It will help you in understanding the concepts better.

Code Example 1

SELECT table_schema as "Database", table_name AS "Table", 
ROUND(((data_length + index_length) / 1024 / 1024), 2) AS "Size (MB)" 
FROM information_schema.TABLES 
WHERE (data_length + index_length) > 1000000 
ORDER BY table_schema, (data_length + index_length) DESC

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