How does mysql count the number of entries in a table?

How does mysql count the number of entries in a table?

The following is a common SQL statement used to count the entries in a table:

Select count (*) from tableName; # orselect count (1) From tableName; # or counts a column, such as IDselect count (ID)

In addition, you can use information_schema to count

MySQL has a database named information_schema, which has a TABLES Table. The main fields of this table are:

 

TABLE_SCHEMA: Database Name

TABLE_NAME: Table Name

ENGINE: The storage ENGINE used

TABLES_ROWS: number of records

DATA_LENGTH: data size

INDEX_LENGTH: Index size

The following SQL statement provides the query method and also counts the information that occupies the storage space:

SELECT information_schema.`TABLES`.TABLE_NAME,       (DATA_LENGTH/1024/1024) as DataM ,    (INDEX_LENGTH/1024/1024) as IndexM,     ((DATA_LENGTH+INDEX_LENGTH)/1024/1024) as AllM,    TABLE_ROWSfrom information_schema.`TABLES` where information_schema.`TABLES`.TABLE_SCHEMA='abc';

Mysql calculates the number of rows in different statuses in a table.

Select status, count (*) from table group by status

A statement used to count the total number of records in all tables in the database (mysql)

<? Php
Mysql_connect ('localhost', 'database account', 'database password ');
Mysql_select_db ('database name ');

$ Result = mysql_query ('show tables '); // obtain all table names

$ All_record = 0;
While ($ record = mysql_fetch_row ($ result )){
$ Tb_name = $ record [0]; // table name

$ N = mysql_result (mysql_query ('select count (*) from ''. $ tb_name. '''), 0 );
$ All_record + = $ n;
}

Echo $ all_record; // total number of records

?>