oracle按日期查詢數量，如果沒有日期數據，默認爲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')

查詢結果：

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

這種查詢數據，用於一種應用場景，統計某個月的某個產品的銷售數量，單表查詢。如果某一天沒有銷售，那麼數據庫當日是沒有數據的，但是我們要的效果卻是想讓當天也查詢出來，數量爲0。這種情況，就把真正的數據查詢出來，跟上面的日期查詢進行right join右關聯查詢，nvl(pnum，0)默認沒有值爲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
    <foreach item="item" index="index" collection="typeList" open="(" separator="," close=")">
        #{item}
    </foreach>
    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 &lt;= TO_DATE(#{etime}, 'YYYY-MM-DD') - TO_DATE(#{btime}, 'YYYY-MM-DD')
    ) b
ON a.createTime=b.DAY_TIME
ORDER BY b.DAY_TIME