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In a previous blog post, we've advertised the use of SQL EXISTS rather than COUNT(*) to check for existence of a value in SQL. I.e. to check if in the Sakila database, actors called WAHLBERG have played in any films, instead of: SELECT count(*) FROM actor a JOIN film_actor fa USING (actor_id) WHERE a.last_name = … Continue reading An Efficient Way to Check for Existence of Multiple Values in SQL →

COUNT function counts the number of rows retrieved by a SELECT statement. The return value is of type BIGINT. The COUNT(expr) function count the number of non-NULL values of expr in the rows retrieved by a SELECT statement. SELECT COUNT(expr) FROM tbl; In contrast, COUNT(*) is different in that it returns a count of the […]

A SELECT statement with COUNT returns the number of rows retrieved by the SELECT statement (see mysql select count). For performance reasons, the desired result is to limit that count. Including a LIMIT clause in the SELECT statement will not work since it only restricts the number of rows returned, which is always one. The […]