oracle invalid format model with comparing dates - oracle

Question

I am trying to run the following query. I am passing the date from a parameter
SELECT to_char(TIMESTAMP, 'HH24') * 1 TIMESTAMP
,sum(TwoG) TwoG
,sum(ThreeG) ThreeG
,sum(FourG) FourG
FROM (
SELECT *
FROM T_CA_Cellsdown
UNION ALL
SELECT *
FROM T_CA_Cellsdown_TFVF
)
WHERE trunc(TIMESTAMP) = trunc(to_date('03-Apr-16', 'dd-Mon-yy'))
AND Type = 'Network'
GROUP BY to_char(TIMESTAMP, 'HH24') * 1
ORDER BY to_char(TIMESTAMP, 'HH24') * 1
Error in query: ORA-01481: invalid number format model
The following query works. I am just trying to change sysdate to a date string which I pass as param through user input in php. Why it is being multiplied by 1 I do not know, it is a query that works and provides the required result.
SELECT to_char(TIMESTAMP, 'HH24') * 1
,sum(TwoG) TwoG
,sum(ThreeG) ThreeG
,sum(FourG) FourG
FROM (
SELECT *
FROM T_CA_Cellsdown
UNION ALL
SELECT *
FROM T_CA_Cellsdown_TFVF
)
WHERE trunc(TIMESTAMP) = trunc(sysdate-1)
AND Type = 'Network'
GROUP BY to_char(TIMESTAMP, 'HH24') * 1
ORDER BY to_char(TIMESTAMP, 'HH24') * 1

Answer 1

The problem is the last line:
ORDER BY to_char(TIMESTAMP, 'HH24') * 1
In the order-by clause it's seeing TIMESTAMP as the column alias from the select list, not as the original TIMESTAMP from the table; so it contains a number, not a timestamp.
So if you had a timestamp where the hours value was 13, say, you're doing
ORDER BY to_char(13, 'HH24') * 1`
... and as the first argument is a number you're using the numeric version of TO_CHAR(), and HH24 isn't a valid format model for that. Which is what the error message says.
You can just do:
ORDER BY TIMESTAMP;
To use your original pattern you'd need to supply a table alias for your inline view, and then use that alias in the order-by, to qualify the TIMESTAMP. By default it's using the column alias version.

Answer 2

order by is executed at last. By the time order by is executed, you are deriving an new column in select statement as timestamp. To overcome it, just use timestamp in order by
SELECT to_char(TIMESTAMP, 'HH24') * 1 TIMESTAMP
,sum(TwoG) TwoG
,sum(ThreeG) ThreeG
,sum(FourG) FourG
FROM (
SELECT *
FROM T_CA_Cellsdown
UNION ALL
SELECT *
FROM T_CA_Cellsdown_TFVF
)
WHERE trunc(TIMESTAMP) = trunc(to_date('03-APR-16', 'dd-Mon-yy'))
AND Type = 'Network'
GROUP BY to_char(TIMESTAMP, 'HH24') * 1
ORDER BY TIMESTAMP -- TIMESTAMP here refers to derived column at line 1
Or use this
SELECT to_char(TIMESTAMP, 'HH24') * 1 TIMESTAMP1 -- Or use different alias
,sum(TwoG) TwoG
,sum(ThreeG) ThreeG
,sum(FourG) FourG
FROM (
SELECT *
FROM T_CA_Cellsdown
UNION ALL
SELECT *
FROM T_CA_Cellsdown_TFVF
)
WHERE trunc(TIMESTAMP) = trunc(to_date('03-APR-16', 'dd-Mon-yy'))
AND Type = 'Network'
GROUP BY to_char(TIMESTAMP, 'HH24') * 1
ORDER BY to_char(TIMESTAMP, 'HH24') * 1
I replicated the issue here. - This will not work.
select to_char(TIMESTAMP, 'HH24') * 1 TIMESTAMP,sum(col1) from
(
select sysdate-1 as TIMESTAMP,1 as col1 from dual
union all
select sysdate-1 as TIMESTAMP,2 as col1 from dual
)
where trunc(sysdate)=trunc(to_date('04-APR-16','Dd-Mon-YY'))
group by to_char(TIMESTAMP, 'HH24') * 1
order by to_char(TIMESTAMP, 'HH24') * 1
But This statement will work.
select to_char(TIMESTAMP, 'HH24') * 1 TIMESTAMP1,sum(col1) from (
select sysdate-1 as TIMESTAMP,1 as col1 from dual
union all
select sysdate-1 as TIMESTAMP,2 as col1 from dual
)
where trunc(sysdate)=trunc(to_date('04-APR-16','Dd-Mon-YY'))
group by to_char(TIMESTAMP, 'HH24') * 1
order by to_char(TIMESTAMP, 'HH24') * 1 --As TIMESTAMP is now reflecting the column from inner table.