![]() Consequently, SELECT COUNT(*) statements only count rows visible to the current transaction. If it did, concurrent transactions might “see” different numbers of rows at the same time. SELECT COUNT(*) FROM cities Ī statement like the one above that invokes the COUNT(*) function without a WHERE clause or additional columns, will perform very fast on MyISAM tables because the number of rows is stored in the table_rows column in the tables table of the information_schema database.įor transactional storage engines such as InnoDB, storing an exact row count is problematic because InnoDB does not keep an internal count of rows in a table. That form of the COUNT() function basically returns the number of rows in a result set returned by a SELECT statement. To counts all of the rows in a table, whether they contain NULL values or not, use COUNT(*). In each case, COUNT() returns a BIGINT that contains either the number of matching rows, or zero, if none were found. The secret is in the function signatures, of which there are several forms: COUNT(*), COUNT(expression) and COUNT(DISTINCT expression). But there’s a little more to it than that, as the COUNT() function can be utilized to count all rows in a table or only those rows that match a particular condition. You probably already know that the COUNT() function returns the number of rows in a table. In part 2, we’ll learn how to obtain a row count from multiple tables, or even from all of the tables within a database. ![]() In today’s tip, we’ll use the native COUNT() function to retrieve the number of rows within one table or view within a MySQL database. Some database management products provide database statistics like table sizes, but it can also be done using straight SQL. There are several ways to get a row count in MySQL.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |