Check out example codes for "mysql count table rows". It will help you in understanding the concepts better.

Code Example 1

select table_name, sum(table_rows) as sum 
from information_schema.tables
where table_schema = '[DB NAME]'
group by table_name 
order by sum desc;

Code Example 2

SELECT sum( case when `tags_Column` CONTAINS 'tag2' then 1 else 0 end ) as tag2,
       sum( case when `tags_Column` CONTAINS 'tag3' then 1 else 0 end ) as tag3,
       .....
       sum( case when `tags_Column` CONTAINS 'tag256' then 1 else 0 end ) as tag256,
       sum( case when `tags_Column` CONTAINS `tag2` OR 
                      `tags_Column` CONTAINS 'tag3`
            then 0 else 1 end ) as doesnt_contains_tags_2_3
FROM `TableContainsTags`

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