oracle:

(Select to_char(a+1-Id,'YYYYMMDD') SHOW_TIME  From (

SELECT rownum Id,to_date( #{endDate,jdbcType=VARCHAR} ,'YYYYMMDD') a FROM DUAL  

CONNECT BY LEVEL <= to_date(#{endDate,jdbcType=VARCHAR},'YYYYMMDD') - to_date(#{startDate,jdbcType=VARCHAR},'YYYYMMDD') +1) Order By SHOW_TIME)  d LEFT JOIN tableA

DB2:

--取指定区间的自然天

with  date_list(SHOW_TIME)  as 

    (select  to_date(#{startDate,jdbcType=VARCHAR},'YYYYMMDD')

            from test.tableA a where  a.USER_ID=#{userId,jdbcType=VARCHAR}

        union all

        select  date_list.SHOW_TIME+1  day

            from test.tableA b ,date_list where b.USER_ID=#{userId,jdbcType=VARCHAR}  and date_list.SHOW_TIME <= to_date( #{endDate,jdbcType=VARCHAR} ,'YYYYMMDD')),

--统计交易

trans_list(transDate,txnCount,txnAmt) as

(select .......)

--外连接获取交易统计数据

select * from  date_list d LEFT JOIN trans_list e