Mybatis查询 动态sql

Mybatis查询 动态sql

• < sql > and < include >

  <sql id="allColumns"> id ,username,birthday,sex,address</sql>
  

  <select id="方法名" resultType="users">
  	select <include refid="allColumns"></include>
      from users
  </select>
  

• < if > and < where >

  <select id="方法名" resultType="users">
  	select <include refid="allColumns"></include>
      from users
      <where>
      	<if test="userName != null and username ="">
  			and username like concat('%'#{username}'%')
          </if>
          <if  test="birthday != null and birthday ="">
              and birthday like concat('%'#{birthday}'%') 
          </if>                                           
      </where>
  </select>           	
  

• < set > 为空的不更新

  <select id="方法名" resultType="users">
  	select <include refid="allColumns"></include>
      from users
      <where>
          <set>
              <if test="userName != null and username ="">
  				and username like concat('%'#{username}'%')
          	</if>
              <if  test="birthday != null and birthday ="">
              	and birthday like concat('%'#{birthday}'%') 
          	</if> 
          </set>
      </where>
  </select>       
  

• < foreach > 循环遍历 循环条件查询 删除 增加 更改

  <select id="方法名" resultType="users">
  	select <include refid="allColumns"></include>
      from users
      <where>  id in
          <foreach collection="array" item="id" separator="," open="(",close=")">
      		#{id}
      	</foreach>
      </where>
  </select>  
  

  • 详解

    • collection:用来指定入参的类型，如果是List集合，则为list，如果为Map集合，则为map，如果是数组，则为array，
    • item：每次循环遍历出来的值或对象
    • separator：多个值或对象或者语句之间的分隔符
    • open：整个循环外的前括号 close：整个循环外面的后括号

    ​