sql 某字段关联今年1-12月月份值查询

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场景模拟：

数据库账务明细表中只存有公司1月和7月的账务明细，比如前端人员有以下需求：给定公司ID返回公司今年1-12月账务汇总，如当月没有数据用0代替，并按月份大小排序。

选定一张行数量大于12的表：

        SELECT
            CASE WHEN length(mon) = 1 THEN concat(LEFT (CURRENT_DATE, 5),'0',mon)
        ELSE
            concat(LEFT(CURRENT_DATE, 5), mon)
        END months
        FROM( SELECT @m :=@m + 1 mon FROM share_sys_area,(SELECT @m := 0) a ) aa LIMIT 12

可以得到一下结果：

使用这种方法进行左连接查询，就可以拿到想要结果：

<select id="getTypeSumByMonth" resultType="map">

    select
        tt.months as mon,
        sum(IFNULL(b.YJ_YY_YJ_COUNT,0)) AS yyyCount,
        sum(IFNULL(b.YJ_YY_YJ_DEBT,0)) / 10000 AS yyyDebt,
        sum(IFNULL(b.YJ_YY_WJ_COUNT,0)) AS yynCount,
        sum(IFNULL(b.YJ_YY_WJ_DEBT,0)) / 10000 AS yynDebt,
        sum(IFNULL(b.YJ_WY_COUNT,0)) AS ynCount,
        sum(IFNULL(b.YJ_WY_DEBT,0)) / 10000 AS ynDebt,
        sum(IFNULL(b.STOP_SLOW_COUNT,0)) AS ssCount,
        sum(IFNULL(b.STOP_SLOW_DEBT,0)) / 10000 AS ssDebt
        from
        (SELECT
            CASE WHEN length(mon) = 1 THEN concat(LEFT (CURRENT_DATE, 5),'0',mon)
        ELSE
            concat(LEFT(CURRENT_DATE, 5), mon)
        END months
        FROM( SELECT @m :=@m + 1 mon FROM share_sys_area,(SELECT @m := 0) a ) aa LIMIT 12) tt

        LEFT JOIN share_acc_project_pro b on tt.months = DATE_FORMAT(b.REPORT_TIME,'%Y-%m')

        <if test="_parameter != null and _parameter !=''">
            AND b.ENT_ID = #{_parameter}
        </if>


        GROUP BY tt.months

</select>

其他思路

RIGHT JOIN (SELECT '01' as time2 from  DUAL UNION ALL  
SELECT '02' as time2 from  DUAL UNION ALL 
SELECT '03' as time2 from  DUAL UNION ALL 
SELECT '04' as time2 from  DUAL UNION ALL 
SELECT '05' as time2 from  DUAL UNION ALL 
SELECT '06' as time2 from  DUAL UNION ALL 
SELECT '07' as time2 from  DUAL UNION ALL 
SELECT '08' as time2 from  DUAL UNION ALL 
SELECT '09' as time2 from  DUAL UNION ALL 
SELECT '10' as time2 from  DUAL UNION ALL 
SELECT '11' as time2 from  DUAL UNION ALL 
SELECT '12' as time2 from  DUAL )