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DQL conditional query
- Condition query: select field list from table name where condition list
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comparison operator
- Equal operator (=)
- specific code
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-- 1.查询姓名为‘杨逍’的员工 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where name = '杨逍';
- Not equal to operator (<> or !=)
- The specific code is as follows
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-- 5.查询密码不等于‘123456’的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where password != '123456';
- greater than operator (>)
- less than operator (<)
- greater than or equal to operator (>=)
- less than or equal to operator (<=)
- The specific code is as follows
-
-- 2.查询id小于等于5的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where id <= 5;
- BETWEEN.....AND....operator (including the most value)
- The specific code is as follows
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-- 6.查询入职日期在‘2000-0-01’(包含)到‘2010-01-01’(包含)之间的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where entrydate between '2000-01-01' and '2010-01-01';
- IN operator
- The specific code is as follows
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-- 8.查询职位是2(讲师),3(学工主管),4(教研主管)的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where job in (2, 3, 4);
- The LIKE operator (placeholder) fuzzy matching uses like (_ matches a single character, % matches a character)
- The specific code is as follows
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-- 9.查询姓名为两个字的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where name like '__';
- IS NULL operator ( without =null )
- The specific code is as follows
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-- 3.查询没有分配职位的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where job is null;
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-- 10.查询性‘张’的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where name like '张%';
- IS NOT NULL operator ( and no !=null )
- The specific code is as follows
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-- 4.查询有职位的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where job is not null;
- Equal operator (=)
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Logical Operators
- AND/&& operator: used to satisfy multiple conditions at the same time.
- The specific code is as follows
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-- 7.查询入职日期在‘2000-0-01’(包含)到‘2010-01-01’(包含)之间且性别为女的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where entrydate between '2000-01-01' and '2010-01-01' and gender = 2;
- OR/|| operator: used to meet any condition.
- The specific code is as follows
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-- 8.查询职位是2(讲师),3(学工主管),4(教研主管)的员工信息 select id, username, password, name, gender, image, job, entrydate, create_time, update_time from tb_emp where job = 2 or 3 or 4;
- NOT/! Operator: Used to negate a condition.
- AND/&& operator: used to satisfy multiple conditions at the same time.
MySQL-DML-condition query
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