mybatis QueryWrapper的条件构造之apply、last、select解析

目录

• QueryWrapper条件构造之apply、last、select
• mysql上的limit使用
• 如果是sqlserver
• 条件构造器QueryWrapper实例
• 案例一
• 案例二
• 案例三
• 案例四

QueryWrapper条件构造之apply、last、select

场景： 查询数据库限制条数时

mysql上的limit使用

QueryWrapper needSyn = new QueryWrapper();
needSyn.ge("ModifyDate",lmtSynRec.getLatestDate());
needSyn.last("limit 200");
List<CusCarInfo> needData = cusCarInfoMapper.selectList(needSyn);

如果是oracle则可以用apply

needSyn.apply("rownum < {0}" , 200);

如果是sqlserver

建议自己写sql查询语句

<select id="getSynList" resultType="com.xmeport.project.model.entity.CusCarInfo">
    select top ${top}  *  from CUS_CAR_INFO t where t.ModifyDate > cast(#{latestDate} as datetime) orderBy 
 t.ModifyDate asc
</select>
List<CusCarInfo> getSynList(int top, Date latestDate);

或者使用QueryWrapper的select

QueryWrapper<CusCarInfo> wrapper  = new QueryWrapper();
wrapper.select("top 200 *");
return this.list(wrapper);

以上就是根据最新时间查询top条数据

传入的字段是时间类型，就用#{} 占位符接收。如果是具体的一个数字或字符可以用 ${ }来接收。

条件构造器QueryWrapper实例

我们再搞几个实例来深入理解下条件构造器QueryWrapper的用法：

案例一

查询姓李的，并且出生日期范围是1993-02-09到1994-04-09的员工

sql实现：

SELECT * FROM t_employee WHERE DATE_FORMAT(birthday,'%Y-%m-%d')>='1993-02-09' AND DATE_FORMAT(birthday,'%Y-%m-%d')<='1994-04-09' AND NAME LIKE '李%'

mp实现：

/**
 * 查询姓李的，并且出生日期范围是1993-02-09到1994-04-09的员工
 * sql：SELECT * FROM t_employee WHERE DATE_FORMAT(birthday,'%Y-%m-%d')>='1993-02-09' AND DATE_FORMAT(birthday,'%Y-%m-%d')<='1994-04-09' AND NAME LIKE '李%'
 */
@Test
public void selectByQueryWrapper3(){
  QueryWrapper<Employee> queryWrapper=new QueryWrapper();
  // QueryWrapper<Employee> queryWrapper2=Wrappers.<Employee>query();
  queryWrapper.apply("DATE_FORMAT(birthday,'%Y-%m-%d')>={0} and DATE_FORMAT(birthday,'%Y-%m-%d')<={1}","1993-02-09","1994-04-09").likeRight("name","李");
  List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
  System.out.println(employeeList);
}

案例二

查询姓李的或者邮箱不为空并且是女性的员工

sql实现：

SELECT * FROM t_employee WHERE NAME LIKE '李%' OR (email IS NOT NULL AND gender ='女')

mp实现：

/**
 * 查询姓李的或者邮箱不为空并且是女性的员工
 * sql：SELECT * FROM t_employee WHERE NAME LIKE '李%' OR (email IS NOT NULL AND gender ='女')
 */
@Test
public void selectByQueryWrapper4(){
  QueryWrapper<Employee> queryWrapper=new QueryWrapper();
  // QueryWrapper<Employee> queryWrapper2=Wrappers.<Employee>query();
  queryWrapper.likeRight("name","李").or(wq->wq.isNotNull("email").eq("gender","女"));
  List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
  System.out.println(employeeList);
}

案例三

查询姓李的并且邮箱不为空或者是女性的员工

sql实现：

SELECT * FROM t_employee WHERE NAME LIKE '李%' AND (email IS NOT NULL OR gender ='女')

mp实现：

/**
 * 查询姓李的并且邮箱不为空或者是女性的员工
 * sql：SELECT * FROM t_employee WHERE NAME LIKE '李%' AND (email IS NOT NULL OR gender ='女')
 */
@Test
public void selectByQueryWrapper5(){
  QueryWrapper<Employee> queryWrapper=new QueryWrapper();
  // QueryWrapper<Employee> queryWrapper2=Wrappers.<Employee>query();
  queryWrapper.likeRight("name","李").and(wq->wq.isNotNull("email").or().eq("gender","女"));
  List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
  System.out.println(employeeList);
}

案例四

查询属于编号1,2,3部门的并且薪水小于等于3500的员工 根据年龄从大到小排序显示

sql实现：

SELECT * FROM t_employee WHERE salary<=3500 AND departmentId IN (1,2,3) ORDER BY birthday ASC

mp实现：

/**
 * 查询属于编号1,2,3部门的并且薪水小于等于3500的员工 根据年龄从大到小排序显示
 * sql：SELECT * FROM t_employee WHERE salary<=3500 AND departmentId IN (1,2,3) ORDER BY birthday ASC
 */
@Test
public void selectByQueryWrapper6(){
  QueryWrapper<Employee> queryWrapper=new QueryWrapper();
  // QueryWrapper<Employee> queryWrapper2=Wrappers.<Employee>query();
  queryWrapper.likeRight("name","李").and(wq->wq.isNotNull("email").or().eq("gender","女"));
  List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
  System.out.println(employeeList);
}

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。