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法律研究获取 MySQL 查询的总行数的最快方法是什么？
您可以使用带有聚合函数 COUNT(*) 的子查询来获取总行数。
我们首先创建一个表 −
mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentFirstName varchar(20), StudentAge int ); Query OK, 0 rows affected (0.48 sec)
使用 insert 命令将一些记录插入表中 −
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('John',23);
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('Larry',21);
Query OK, 1 row affected (0.40 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('Johnny',23);
Query OK, 1 row affected (0.43 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('Chris',21);
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('David',23);
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('James',21);
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('Jace',24);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('Mike',21);
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('Robert',25);
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable(StudentFirstName,StudentAge) values('Mike',22);
Query OK, 1 row affected (0.23 sec)以下是使用 select 语句显示表中所有记录的查询 −
mysql> select *from DemoTable;
这会产生以下输出 −
+-----------+------------------+------------+ | StudentId | StudentFirstName | StudentAge | +-----------+------------------+------------+ | 1 | John | 23 | | 2 | Larry | 21 | | 3 | Johnny | 23 | | 4 | Chris | 21 | | 5 | David | 23 | | 6 | James | 21 | | 7 | Jace | 24 | | 8 | Mike | 21 | | 9 | Robert | 25 | | 10 | Mike | 22 | +-----------+------------------+------------+ 10 rows in set (0.00 sec)
以下是获取 MySQL 查询所有行计数的查询，针对所有列都设置了值 −
mysql> select StudentFirstName,(select count(*) from DemoTable) AS Total_Count from DemoTable limit 10;
这会产生以下输出 −
+------------------+-------------+ | StudentFirstName | Total_Count | +------------------+-------------+ | John | 10 | | Larry | 10 | | Johnny | 10 | | Chris | 10 | | David | 10 | | James | 10 | | Jace | 10 | | Mike | 10 | | Robert | 10 | | Mike | 10 | +------------------+-------------+ 10 rows in set (0.03 sec)
更新于： 30-Jul-2019
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