mysql select and count

SQL tuning is primarily about reducing the number of consistent gets and physical reads. COUNT (1) is compared with COUNT (*): If your datasheet does not have a primary key, then count (1) is faster than COUNT (*)If you have a primary key, the

The table structure is as follows: The code is as follows Copy Code Mysql> Show CREATE TABLE Userg;1. Row ***************************Table:userCreate table:create Table ' user ' (' ID ' int (a) unsigned not NULL

The table structure is as follows:Mysql> Show CREATE TABLE user\g;*************************** 1. Row *************************** table:usercreate table:create Table ' user ' ( ' id ' int (ten) unsigned not NULL AUTO _increment, ' name '

Tested under MySQL 5.6.MyISAM Engine:When creating a data table, MySQL generates 3 files, respectively (table: Test):TEST.FRM, Test. MYD, Test. Myi file,TEST.FRM is the table structure, Test.myd is the file that holds the data, Test.myi is the file

  1. select count (*) FROM tablename is the optimal choice under any circumstances; 2. Minimize select count (*) FROM tablename where col = 'value' queries; 3. prevent the appearance of select count (COL) FROM tablename.     COUNT (*) and COUNT (COL)

Mysql count details and function instance code, mysqlcount Mysql count details The count function is a function used to count records in tables or arrays. The following describes how to use the count function in mysql. Count (*) returns the number

In MySQL found_rows () and COUNT (*) can be recorded, if all the same why there are two such functions, I would like to introduce the Select Found_rows () and the Count (*) Usage differenceIt is often possible to return rows with limit restrictions

1. Test Environment OS: LinuxDB: mysql-5.5.18Table: innodb Storage Engine The table is defined as follows: 2. test scenario and analysis [number of group_message records in the statistical table] (1) select count (*) Method (2) select count

In MySQL found_rows () and COUNT (*) can be recorded, if all the same why there are two such functions, I would like to introduce the Select Found_rows () and the Count (*) Usage differenceIt is often possible to return rows with limit restrictions

Summary of differences between count (*), count (1), and count (col) in MySQL, mysqlcol Preface The count function is a function used to count records in tables or arrays. count (*) returns the number of rows to be retrieved, whether or not it