1.sql片段(自己在mybatis的xml文件中定义下面的的语句,这个sql片段的的作用是动态where语句)

<sql id="query_where">  --sql片段的名称
        <where>
            <if test="operateUser != null and operateUser != ''">
                and operate_user = #{operateUser}
            </if>
            <if test="operateMethod != null and operateMethod != ''">
                and operate_method = #{operateMethod}
            </if>
            <if test="returnClass != null and returnClass != ''">
                and return_class = #{returnClass}
            </if>
            <if test="costTime != null">
                and cost_time = #{costTime}
            </if>
        </where>
    </sql>

2.怎么引用 !!!(利用)

  <select id="countByCondition" resultType="long" parameterType="map">
        SELECT COUNT(*) FROM `operation_log`
        <include refid="query_where"></include> 
    </select>

**sql片段主要是解决冗余的代码片段,减少开发,使代码整洁、高效

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