Answers for "sql count by"

sql count

/*COUNT(column_name) will return the number of rows from the column 
that are not NULL*/
SELECT COUNT(column_name)
FROM table_name;

/*COUNT(*) will return the number of rows from the table*/
SELECT COUNT(*)
FROM table_name;

sql count where

SELECT count(CASE WHEN gender = 'F' THEN 1 ELSE NULL END) women_count,
       count(CASE WHEN gender = 'M' THEN 1 ELSE NULL END) men_count
FROM people;