oracle按日期查询数量，如果没有日期数据，默认为0

SELECT  TO_CHAR(TO_DATE('2019-08-01', 'YYYY-MM-DD') + ROWNUM - 1, 'YYYY-MM-DD') DAY_TIME
FROM DUAL
CONNECT BY ROWNUM <= TO_DATE('2019-09-01', 'YYYY-MM-DD') - TO_DATE('2019-08-01', 'YYYY-MM-DD')

查询结果：

2019-08-01
2019-08-02
2019-08-03
2019-08-04
2019-08-05
2019-08-06
2019-08-07
2019-08-08
2019-08-09
2019-08-10
2019-08-11
2019-08-12
2019-08-13
2019-08-14
2019-08-15
2019-08-16
2019-08-17
2019-08-18
2019-08-19
2019-08-20
2019-08-21
2019-08-22
2019-08-23
2019-08-24
2019-08-25
2019-08-26
2019-08-27
2019-08-28
2019-08-29
2019-08-30
2019-08-31

这种查询数据，用于一种应用场景，统计某个月的某个产品的销售数量，单表查询。如果某一天没有销售，那么数据库当日是没有数据的，但是我们要的效果却是想让当天也查询出来，数量为0。这种情况，就把真正的数据查询出来，跟上面的日期查询进行right join右关联查询，nvl(pnum，0)默认没有值为0，即可。

SELECT nvl(a.pnum,0) as pnum,b.DAY_TIME as createTime from (
    SELECT createTime,sum(pnum) pnum FROM (
    SELECT to_char(t.CREATE_TIME,'yyyy-mm-dd') createTime,t.type_code typeCode,COUNT(1) pnum
    FROM prot_sale
    WHERE t.CREATE_TIME >= TO_DATE(#{btime}, 'YYYY-MM-DD')
    AND t.CREATE_TIME <= TO_DATE(#{etime}, 'YYYY-MM-DD')
    AND t.type_code IN
    
        #{item}
    
    GROUP BY to_char(t.CREATE_TIME,'yyyy-mm-dd'),t.type_code
    ORDER BY to_char(t.CREATE_TIME,'yyyy-mm-dd') asc
    ) GROUP BY createTime
  ) a
right join
  (SELECT  TO_CHAR(TO_DATE(#{btime}, 'YYYY-MM-DD') + ROWNUM - 1, 'YYYY-MM-DD') DAY_TIME
    FROM DUAL
    CONNECT BY ROWNUM <= TO_DATE(#{etime}, 'YYYY-MM-DD') - TO_DATE(#{btime}, 'YYYY-MM-DD')
    ) b
ON a.createTime=b.DAY_TIME
ORDER BY b.DAY_TIME