Some time ago, Era shared with you a Mysql database repeat detection function. For how to use this function, you can move to "Repeat detection function when mqsql data is stored in the database-php". today we will introduce two methods to count the
The convenient way to count the total number of rows in the query result in MYSQL saves the keyword count (*) bitsCN. comMYSQL:
After checking the manual, we found that this keyword is used to count the total number of results
After checking the manual, we can find that the SQL _CALC_FOUND_ROWS keyword is used to count the total number of results that meet the filtering conditions (not limited by Limit, if you are interested, you can learn the MYSQL Keyword: SQL
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
Mysql queries non-duplicated row content and the number of non-Repeated Records count. distinct has such a table that records id, p_id, p_name, p_content, p_time 1 343 aaa aaaaaa 2012-09-01 2 344 bbb bbbbbb 2012-09-02 3 321 ccc cccccccc 2012-09-03
Usage of the count function in MySQL
The count function is a function used to count records in tables or arrays. Here we will introduce the usage and Performance Comparison of the count function in MySQL. Count (*) returns the number of rows to be
Mysql -- SQL Optimization-count the number of Certain types and the number of mysqlsql Optimizations
Sometimes we want to count the number of such SQL statements. In addition to full table scanning, filesort takes 1.34 seconds.
I. User table information
Use the query statement: Select count (1) from user; Use the explain statement to check whether the statement is indexed. the following result shows the query time of the statement.
Data Volume query
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
The count function is a function used to count records in tables or arrays. Here we will introduce the usage and Performance Comparison of the count function in mysql.
Count (*) returns the number of rows to be retrieved, whether or not it contains
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