Mysql范围查询

当查询结果在一定范围内，即有多条数据匹配查询条件时称为范围查询。唯一查询可以看成是特殊的范围查询，范围内只有一条数据。

通常where条件中使用了=, >, =, desc emps; +------------+---------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------+---------------+------+-----+---------+----------------+ | id | int | NO | PRI | NULL | auto_increment | | emp_no | int | YES | | NULL | | | birth_date | date | YES | | NULL | | | first_name | varchar(14) | YES | | NULL | | | last_name | varchar(16) | YES | | NULL | | | gender | enum('M','F') | YES | | NULL | | | hire_date | date | YES | | NULL | | +------------+---------------+------+-----+---------+----------------+ 7 rows in set (0.00 sec) mysql> show table status like 'emps'\G *************************** 1. row *************************** Name: emps Engine: InnoDB Version: 10 Row_format: Dynamic Rows: 299440 Avg_row_length: 54 Data_length: 16269312 Max_data_length: 0 Index_length: 5783552 Data_free: 2097152 Auto_increment: 327676 Create_time: 2023-05-26 12:09:47 Update_time: 2023-05-26 12:07:09 Check_time: NULL Collation: utf8mb4_0900_ai_ci Checksum: NULL Create_options: Comment: 1 row in set (0.00 sec) mysql> select count(1) from emps; +----------+ | count(1) | +----------+ | 300024 | +----------+ 1 row in set (0.01 sec) mysql> show indexes from emps; +-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression | +-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ | emps | 0 | PRIMARY | 1 | id | A | 299341 | NULL | NULL | | BTREE | | | YES | NULL | | emps | 0 | emp_no_uk | 1 | emp_no | A | 299341 | NULL | NULL | YES | BTREE | | | YES | NULL | +-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ 2 rows in set (0.00 sec)