mybatis-特殊查询

特殊SQL的执行

模糊查询

/**
 * 根据用户名进行模糊查询
 * @param username 
 * @return java.util.List<com.atguigu.mybatis.pojo.User>
 * @date 2022/2/26 21:56
 */
List<User> getUserByLike(@Param("username") String username);

<!--List<User> getUserByLike(@Param("username") String username);-->
<select id="getUserByLike" resultType="User">
	<!--select * from t_user where username like '%${mohu}%'-->  
	<!--select * from t_user where username like concat('%',#{mohu},'%')-->  
	select * from t_user where username like "%"#{mohu}"%"
</select>

• 其中select * from t_user where username like "%"#{mohu}"%"是最常用的

批量删除

• 只能使用${}，如果使用#{}，则解析后的sql语句为delete from t_user where id in ('1,2,3')，这样是将1,2,3看做是一个整体，只有id为1,2,3的数据会被删除。正确的语句应该是delete from t_user where id in (1,2,3)，或者delete from t_user where id in ('1','2','3')

/**
 * 根据id批量删除
 * @param ids 
 * @return int
 * @date 2022/2/26 22:06
 */
int deleteMore(@Param("ids") String ids);

<delete id="deleteMore">
	delete from t_user where id in (${ids})
</delete>

//测试类
@Test
public void deleteMore() {
	SqlSession sqlSession = SqlSessionUtils.getSqlSession();
	SQLMapper mapper = sqlSession.getMapper(SQLMapper.class);
	int result = mapper.deleteMore("1,2,3,8");
	System.out.println(result);
}

动态设置表名

• 只能使用${}，因为表名不能加单引号

/**
 * 查询指定表中的数据
 * @param tableName 
 * @return java.util.List<com.atguigu.mybatis.pojo.User>
 * @date 2022/2/27 14:41
 */
List<User> getUserByTable(@Param("tableName") String tableName);

<!--List<User> getUserByTable(@Param("tableName") String tableName);-->
<select id="getUserByTable" resultType="User">
	select * from ${tableName}
</select>

测试类代码

package com.atguigu.mybatis.test;


import com.atguigu.mybatis.mapper.SqlMapper;
import com.atguigu.mybatis.pojo.user;
import com.atguigu.mybatis.utils.sqlSessionUtils;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class SQLMapperTest {
    @Test
    public void testGetUserByLike(){
        SqlSession sqlSession = sqlSessionUtils.GetSqlSession();
        SqlMapper mapper = sqlSession.getMapper(SqlMapper.class);
        List<user> a = mapper.getUserByLike1("a");
        System.out.println(a);

    }
    @Test
    public void testDeleteMore(){
        SqlSession sqlSession = sqlSessionUtils.GetSqlSession();
        SqlMapper mapper = sqlSession.getMapper(SqlMapper.class);
        int resoult = mapper.deleteMore("1,2,3");
        System.out.println(resoult);
    }
    @Test
    public void testGetUserByTableName(){
        SqlSession sqlSession = sqlSessionUtils.GetSqlSession();
        SqlMapper mapper = sqlSession.getMapper(SqlMapper.class);
        List<user> t_user = mapper.getUserByTableName("t_user");
        System.out.println(t_user);
    }

}