MySQL

# show databases...ordered by MB size
    SELECT
        table_schema "DB Name",
        Round(Sum(data_length + index_length) / 1024 / 1024, 1) "DB Size in MB"
    FROM
        information_schema.tables
    GROUP BY
        table_schema
    ORDER BY 2 DESC;


# show database tables...ordered by MB size
    SELECT
        table_schema AS `Database`,
        TABLE_NAME   AS `Table`,
        round(((data_length + index_length) / 1024 / 1024), 2) `Size in MB`
    FROM
        information_schema.TABLES
    ORDER BY
        3 DESC
    LIMIT 5;