生成的字符串属性上的POSTGRESQL联接

我得到了一个名为

work\u schema\u items

的表，其中包含两列，这个问题的重要一列是varchar column weekday。包含以下值：

end_time    start_time    weekday
12:00       06:00         Monday
14:30       12:30         Monday
15:00       14:45         Monday
18:00       15:00         Monday
21:00       18:30         Monday
23:00       21:15         Monday
23:59       23:15         Monday
12:00       06:00         Tuesday
14:30       12:30         Tuesday
15:00       14:45         Tuesday
18:00       15:00         Tuesday
21:00       18:30         Tuesday
23:00       21:15         Tuesday
23:59       23:15         Tuesday
12:00       06:00         Wednesday
14:30       12:30         Wednesday
15:00       14:45         Wednesday
18:00       15:00         Wednesday
21:00       18:30         Wednesday
23:00       21:15         Wednesday
23:59       23:15         Wednesday
12:00       06:00         Thursday
14:30       12:30         Thursday
15:00       14:45         Thursday
18:00       15:00         Thursday
21:00       18:30         Thursday
23:00       21:15         Thursday
23:59       23:15         Thursday
12:00       06:00         Friday
14:30       12:30         Friday
15:00       14:45         Friday
18:00       15:00         Friday
21:00       18:30         Friday
23:00       21:15         Friday
23:59       23:15         Friday

运行以下sql查询时：

select 
    t.date,
    t.weekday,
    work_schema_items.weekday
from (
    select
        dd::date as date,
        to_char(dd, 'Day')::varchar as weekday
    from 
        generate_series('2019-12-08'::timestamp, '2019-12-16'::timestamp, '1 day'::interval) dd
    ) as t
left join work_schema_items on t.weekday = work_schema_items.weekday
order by date

我得到这个结果：

2019-12-08  Sunday      NULL
2019-12-09  Monday      NULL
2019-12-10  Tuesday     NULL
2019-12-11  Wednesday   Wednesday
2019-12-11  Wednesday   Wednesday
2019-12-11  Wednesday   Wednesday
2019-12-11  Wednesday   Wednesday
2019-12-11  Wednesday   Wednesday
2019-12-11  Wednesday   Wednesday
2019-12-11  Wednesday   Wednesday
2019-12-12  Thursday    NULL
2019-12-13  Friday      NULL
2019-12-14  Saturday    NULL
2019-12-15  Sunday      NULL
2019-12-16  Monday      NULL

我期望得到的是每天的工作日值，就像我在星期三做的一样。为什么只有星期三才正确地连接起来？我做错了什么

谢谢，我找到了解决办法

char

是固定长度的数据类型，星期三是最长的工作日字符串。即使我将其转换为

varchar

，它仍保持其宽度，这导致我尝试将

“周一”

加入到

“周一”

一个简单的TRIM（）解决了这个问题：

select 
    t.date,
    t.weekday,
    work_schema_items.weekday
from (
    select
        dd::date as date,
        TRIM(to_char(dd, 'Day')::varchar) as weekday
    from 
        generate_series('2019-12-08'::timestamp, '2019-12-16'::timestamp, '1 day'::interval) dd
    ) as t
left join work_schema_items on t.weekday = work_schema_items.weekday
order by date