mybatis .xml SQL count(1) 和SUM函数的简单使用

数据库MySQL
代码示例：
problemMapper.xml

<select id="qureyProblemCount" resultType="java.util.HashMap">
        SELECT
        COUNT(1) AS totalCount,
        SUM (CASE WHEN PROBLEM_LEVEL='1' THEN 1 ELSE 0 END) AS aCount,
        SUM(CASE WHEN PROBLEM_LEVEL='2' THEN 1 ELSE 0 END) AS bCount,
        SUM(CASE WHEN PROBLEM_LEVEL='3' THEN 1 ELSE 0 END) AS cCount,
        SUM(CASE WHEN PROBLEM_LEVEL='4' THEN 1 ELSE 0 END) AS dCount,
        SUM(CASE WHEN PROBLEM_LEVEL='5' THEN 1 ELSE 0 END) AS eCount
        FROM problemTable
        <where>
        <if test="problemSource!=null and problemSource!=''">
            PROBLEM_SOURCE = #{problemSource}
        </if>
        <if test="problemNoList!=null and problemNoList!='' and problemNoList.size>0">
            AND CAR_FRAME_NO IN
            <foreach item="carFrameNo" collection="problemNoList" open="(" separator="," close=")" index="index">
                #{carFrameNo}
            </foreach>
        </if>
        </where>
    </select>

problemMapper.java

Map<String, Object> qureyProblemCount(@Param("problemNoList")List<String> problemNoList, @Param("problemSource") String problemSource);

COUNT(1)默认返回类型是Long
SUM默认返回类型是BigDecimal
在写返回类型时应该注意，Integer可能会报错。

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