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需求背景

一个统计接口，前端需要返回两个数组，一个是0-23的小时计数，一个是各小时对应的统计数。

思路

1. 直接使用group by查询要统计的表，当某个小时统计数为0时，会没有该小时分组。思考了一下，需要建立辅助表，只有一列小时，再插入0-23共24个小时

CREATE TABLE hours_list (    hour int NOT NULL PRIMARY KEY)

2. 先查小时表，再做连接需要查的表，即可将没有统计数的小时填充上0。这里由于需要查多个表中，create_time在每个小时区间内、且SOURCE_ID等于查询条件的统计之和，所以UNION ALL了多张表

SELECT			    t.HOUR,			    sum(t.HOUR_COUNT) hourCount			FROM                (SELECT                    hs. HOUR AS HOUR,                    COUNT(cs.RECORD_ID) AS HOUR_COUNT                FROM                    cbc_hours_list hs                LEFT JOIN cbc_source_0002 cs ON HOUR (cs.create_time) = hs. HOUR                AND cs.create_time > #{startTime}                AND cs.create_time <= #{endTime}                <#if sourceId?exists && sourceId !=''>                    AND SOURCE_ID = #{sourceId}                
                   GROUP BY                    hs. HOUR                UNION ALL                SELECT                    hs.HOUR AS HOUR,                    COUNT(cs.RECORD_ID) AS HOUR_COUNT                FROM                    cbc_hours_list hs                LEFT JOIN cbc_source_hs cs ON HOUR (cs.create_time) = hs. HOUR                AND cs.create_time > #{startTime}                AND cs.create_time <= #{endTime}                <#if sourceId?exists && sourceId !=''>                    AND SOURCE_ID = #{sourceId}                
                   GROUP BY                    hs. HOUR                UNION ALL                SELECT                    hs.HOUR AS HOUR,                    COUNT(cs.RECORD_ID) AS HOUR_COUNT                FROM                    cbc_hours_list hs                LEFT JOIN cbc_source_kfyj cs ON HOUR (cs.create_time) = hs. HOUR                AND cs.create_time > #{startTime}                AND cs.create_time <= #{endTime}                <#if sourceId?exists && sourceId !=''>                    AND SOURCE_ID = #{sourceId}                
                   GROUP BY                    hs. HOUR                UNION ALL                SELECT                    hs.HOUR AS HOUR,                    COUNT(cs.RECORD_ID) AS HOUR_COUNT                FROM                    cbc_hours_list hs                LEFT JOIN cbc_source_his_0002 cs ON HOUR (cs.create_time) = hs. HOUR                AND cs.create_time > #{startTime}                AND cs.create_time <= #{endTime}                <#if sourceId?exists && sourceId !=''>                    AND SOURCE_ID = #{sourceId}                
                   GROUP BY                    hs. HOUR                UNION ALL                SELECT                    hs.HOUR AS HOUR,                    COUNT(cs.RECORD_ID) AS HOUR_COUNT                FROM                    cbc_hours_list hs                LEFT JOIN cbc_source_his_hs cs ON HOUR (cs.create_time) = hs. HOUR                AND cs.create_time > #{startTime}                AND cs.create_time <= #{endTime}                <#if sourceId?exists && sourceId !=''>                    AND SOURCE_ID = #{sourceId}                
                   GROUP BY                    hs. HOUR                UNION ALL                SELECT                    hs.HOUR AS HOUR,                    COUNT(cs.RECORD_ID) AS HOUR_COUNT                FROM                    cbc_hours_list hs                LEFT JOIN cbc_source_his_kfyj cs ON HOUR (cs.create_time) = hs. HOUR                AND cs.create_time > #{startTime}                AND cs.create_time <= #{endTime}                <#if sourceId?exists && sourceId !=''>                    AND SOURCE_ID = #{sourceId}                
                   GROUP BY                    hs. HOUR) t            GROUP BY                t.hour

效果

统计数为0的小时也可以查出来了。

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