To use the COUNT and GROUP BY functions in MySQL to count the number of rows in a table based on a specific column and then sum all of the counts, you can use the following query:
SELECT COUNT(*), <column>
FROM <table>
GROUP BY <column>
WITH ROLLUP;
The COUNT(*) function will count the number of rows in the table, while the <column> variable specifies the column you want to group by. The GROUP BY function groups the results based on the specified column.
The WITH ROLLUP clause at the end of the query will add an extra row to the result set that shows the total for each group. This row will have a NULL value for the <column> variable.
To sum all of the counts, you can use the SUM function on the COUNT(*) column in a subquery:
SELECT SUM(counts)
FROM (
SELECT COUNT(*) AS counts, <column>
FROM <table>
GROUP BY <column>
) AS counts_table;
This query first uses the COUNT(*) function and the GROUP BY function to count the number of rows for each value in the specified column, and then aliases the resulting count as counts. The outer query then uses the SUM function to add up all of the counts values from the subquery.
