More columns also required adding to the GROUP BY portion of the query. ![]() I ran across this while trying to perform a similar task with a query containing about a dozen columns. 5 Examples of Using COUNT() with GROUP BY Now that we’ve gone through the basic scenarios where COUNT() and GROUP BY are used, let’s go over some of the more complicated examples. I do believe my approach is a bit easier to follow. It is often used to retrieve the total number of records in a table or to calculate the number of occurrences of a particular value within a column. That is still significantly slower then the other two queries. This aggregate function returns all rows or only rows matched to specified conditions if there is no row that matches, it returns 0. This function does not count the NULL values. To get the row count of a single table, you use the COUNT () in a SELECT statement as follows: SELECT COUNT () FROM tablename Code language: SQL (Structured Query Language) (sql) For example, to get the number of rows in the customers table in the sample database, you use the following statement. The MySQL COUNT () function provides several records in the result set from a table when an SQL SELECT statement is executed. Adding a key to the user_id on the posts and pages tables avoids the file sort and sped up the slow query to only take 18 seconds. The COUNT() method is used to count the number of rows residing in the table or count the number of rows according to the given condition. Getting MySQL row count of a single table. Using EXPLAIN with each of the queries shows that both of your approaches involves a filesort which is avoided with my query. Your updated simpler method took over 2000 times as long (nearly 3 minutes compared to. For statements which return a result set (such as SELECT, SHOW, DESC or HELP ), returns -1, even when the result set is. This is the same as the row count that the mariadb client displays and the value from the mysqlaffectedrows () C API function. Limited testing showed nearly identical performance with this query to your query using left join to select subqueries. ROWCOUNT () returns the number of rows updated, inserted or deleted by the preceding statement. ![]() To test performance differences, I loaded the tables with 16,000 posts and nearly 25,000 pages. (select count(*) from pages where er_id=er_id) as page_count ![]() (select count(*) from posts where er_id=er_id) as post_count, My solution involves the use of dependent subqueries. select concat('select ',tablename,', count() from ',tablename,' ') from informationschema. Or just for one specific: SELECT NUM, COUNT () AS count FROM yourTable WHERE NUM1. INSERT INTO users (name) VALUES ( 'Jen ') ĬREATE TABLE posts (post_id INT PRIMARY KEY AUTO_INCREMENT, user_id INT) ĬREATE TABLE pages (page_id INT PRIMARY KEY AUTO_INCREMENT, user_id INT) If you want to have the result for all values of NUM: SELECT NUM, COUNT () AS count FROM yourTable GROUP BY NUM. INSERT INTO users (name) VALUES ( 'Simon ') INSERT INTO users (name) VALUES ( 'Matt ') CREATE TABLE users (user_id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR( 20))
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