Where-clause for date-string

Question

Hi specialist's,
i have a simple question about a select, but I think I do not see the forrest becaus of too many trees ...
I have a table where timestamps are stored in seconds-since-epoch.
I select a human readble format with this statement:
select to_char(DATE '1970-01-01' + TRXTIMESTAMP / (24*3600*1000), 'DD-MM-YYYY HH24:MI:SS')  as timestamp from txlog;
TIMESTAMP
19-10-2013 09:31:27
19-10-2013 09:31:27
19-10-2013 09:31:27
Now I want to filter i.e. for dates of 19-01.... 
My first try was this:
select to_char(DATE '1970-01-01' + TRXTIMESTAMP / (24*3600*1000), 'DD-MM-YYYY HH24:MI:SS')  as timestamp from txlog
  where timestamp like '19-%'
Result:
ORA-00904: "TIMESTAMP": invalid identifier
My next try was this:
select to_char(DATE '1970-01-01' + TRXTIMESTAMP / (24*3600*1000), 'DD-MM-YYYY HH24:MI:SS')  as timestamp from txlog
where 1 like '19%'
Result: 0 rows!
If I change this to
... where 1 like '%'
I get all rows.
What is wrong with my selects ???

Answer 1

Felix_GG wrote:
Hi specialist's,
i have a simple question about a select, but I think I do not see the forrest becaus of too many trees ...
I have a table where timestamps are stored in seconds-since-epoch.
I select a human readble format with this statement:
select to_char(DATE '1970-01-01' + TRXTIMESTAMP / (24*3600*1000), 'DD-MM-YYYY HH24:MI:SS')  as timestamp from txlog;
TIMESTAMP
19-10-2013 09:31:27
19-10-2013 09:31:27
19-10-2013 09:31:27
Now I want to filter i.e. for dates of 19-01....
My first try was this:
select to_char(DATE '1970-01-01' + TRXTIMESTAMP / (24*3600*1000), 'DD-MM-YYYY HH24:MI:SS')  as timestamp from txlog
  where timestamp like '19-%'
Result:
ORA-00904: "TIMESTAMP": invalid identifier
My next try was this:
select to_char(DATE '1970-01-01' + TRXTIMESTAMP / (24*3600*1000), 'DD-MM-YYYY HH24:MI:SS')  as timestamp from txlog
where 1 like '19%'
Result: 0 rows!
If I change this to
... where 1 like '%'
I get all rows.
What is wrong with my selects ???
Firstly, why not store timestamps as timestamps?
Anyway, Your first select refers to the alias 'timestamp' which is only accessible in an outer query, not from within the where clause.
Try
Select * from (
select to_char(DATE '1970-01-01' + TRXTIMESTAMP / (24*3600*1000), 'DD-MM-YYYY HH24:MI:SS')  as timestamp from txlog
where timestamp like '19-%';
But timestamp is not a good choice for an alias, as it is a keyword.
Your second select is obvious - the number 1 will never be like '19%', but it will work
in the third select: as 1 is indeed like '%' (anything).