SQL Custom unique Ordering with repeated sequence - sql

Question

I have a datetime column (data type of timestamp without time zone) named time. I can best explain my issue with a example:
Example I've the following data in this column (pretifying timestamp for this example)
ID TIME
1 1 Mar 2022 - 1PM
2 1 Mar 2022 - 2PM
3 1 Mar 2022 - 1PM
4 1 Mar 2022 - 3PM
5 1 Mar 2022 - 2PM
6 2 Mar 2022 - 2PM
7 2 Mar 2022 - 1PM
8 2 Mar 2022 - 3PM
9 2 Mar 2022 - 1PM
10 1 Mar 2022 - 3PM
11 2 Mar 2022 - 2PM
12 2 Mar 2022 - 3PM
13 3 Mar 2022 - 4PM
14 3 Mar 2022 - 3PM
15 3 Mar 2022 - 3PM
16 3 Mar 2022 - 4PM
If i do ORDER BY time, i get the following result:
ID TIME
1 1 Mar 2022 - 1PM
3 1 Mar 2022 - 1PM
2 1 Mar 2022 - 2PM
5 1 Mar 2022 - 2PM
4 1 Mar 2022 - 3PM
10 1 Mar 2022 - 3PM
7 2 Mar 2022 - 1PM
9 2 Mar 2022 - 1PM
6 2 Mar 2022 - 2PM
11 2 Mar 2022 - 2PM
8 2 Mar 2022 - 3PM
12 2 Mar 2022 - 3PM
14 3 Mar 2022 - 3PM
15 3 Mar 2022 - 3PM
13 3 Mar 2022 - 4PM
16 3 Mar 2022 - 4PM
But i want the result in this way:
ID TIME
1 1 Mar 2022 - 1PM
2 1 Mar 2022 - 2PM
4 1 Mar 2022 - 3PM
13 3 Mar 2022 - 4PM
3 1 Mar 2022 - 1PM
5 1 Mar 2022 - 2PM
10 1 Mar 2022 - 3PM
16 3 Mar 2022 - 4PM
7 2 Mar 2022 - 1PM
6 2 Mar 2022 - 2PM
8 2 Mar 2022 - 3PM
9 2 Mar 2022 - 1PM
11 2 Mar 2022 - 2PM
12 2 Mar 2022 - 3PM
14 3 Mar 2022 - 3PM
13 3 Mar 2022 - 4PM
As you can see first 4 rows have unique timestamp and the sequence should repeat based on Time (1PM, 2PM, 3PM).
How can we do this in SQL? I'm using postresql as my DB. I'm using Rails for my Backend.
EDIT:
Have added more context to example to explain my scenario.

Answer 1

One way you can try to use ROW_NUMBER window function with REPLACE function
SELECT time
FROM (
SELECT *,REPLACE(time,'PM','') val,
ROW_NUMBER() OVER(PARTITION BY REPLACE(time,'PM','')) rn
FROM T
) t1
ORDER BY rn,val

Answer 2

For example, sequence of the col a
with tbl(a, othercol) as
(
SELECT 1,1 UNION ALL
SELECT 1,2 UNION ALL
SELECT 1,3 UNION ALL
SELECT 2,4 UNION ALL
SELECT 2,5 UNION ALL
SELECT 2,6 UNION ALL
SELECT 3,7 UNION ALL
SELECT 3,8 UNION ALL
SELECT 3,9
),
cte as (
SELECT *, row_number() over(partition by a order by a) rn
from tbl
)
select a, othercol
from cte
order by rn, a

Answer 3

The problem you have at hand is a direct result of not choosing the correct data type for the values you store.
To get the sorting correct, you need to convert the string to a proper time value. There is no to_time() function in Postgres, but you can convert it to a timestamp then cast it to a time:
order by to_timestamp("time", 'hham')::time
You should fix your database design and convert that column to a proper time type. Which will also prevent storing invalid values ('3 in the afternoon' or '128foo') in that column