More on unique vs distinct

Not 100% sure....

select count(*) from (select distinct source_id from obis_sources) t

Wm.A.Stafford wrote:

On Nov 20, 2006, at 12:27 PM, Wm.A.Stafford wrote:

I guess I should have been a bit more specific. Here is an example
of the type of query I'm finding in the Oracle app and the results
of my attempt to find a PostgreSQL equivalent.

select count(unique 'source_id') from obis_sources;
pgAdmin III query responds:
ERROR: syntax error at or near "'source_id'" at character 23

select count(distinct 'source_id') from obis_sources;
pgAdmin III query responds:
ERROR: could not identify an equality operator for type "unknown"

The single quotes are confusing things here, it treats 'source_id' as
a literal string instead of a column name. Try it without the quotes:

select count(distinct source_id) from obis_sources;

hth,

-Casey

On Mon, 2006-11-20 at 19:46 -0300, Rodrigo Gonzalez wrote:

Not 100% sure....

select count(*) from (select distinct source_id from obis_sources) t

SELECT count(source_id) FROM obis_sources GROUP BY source_id ?

Joshua D. Drake

Wm.A.Stafford wrote:

I guess I should have been a bit more specific. Here is an example of
the type of query I'm finding in the Oracle app and the results of my
attempt to find a PostgreSQL equivalent.

select count(unique 'source_id') from obis_sources;
pgAdmin III query responds:
ERROR: syntax error at or near "'source_id'" at character 23

select count(distinct 'source_id') from obis_sources;
pgAdmin III query responds:
ERROR: could not identify an equality operator for type "unknown"

Thanks for all the help,
-=bill

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On Nov 21, 2006, at 5:27 , Wm.A.Stafford wrote:

I guess I should have been a bit more specific. Here is an example
of the type of query I'm finding in the Oracle app and the results
of my attempt to find a PostgreSQL equivalent.

select count(unique 'source_id') from obis_sources;
pgAdmin III query responds:
ERROR: syntax error at or near "'source_id'" at character 23

select count(distinct 'source_id') from obis_sources;
pgAdmin III query responds:
ERROR: could not identify an equality operator for type "unknown"

I think the single quotes are the cause of your problem. Single-
quotes indicate a string literal. In the first case, you can see that
the syntax error is putting double quotes around 'source_id',
including the single quotes, because it's expecting an identifier
(not a string literal). In the second case it's seeing a string
literal but it's not sure what type to implicitly cast it to.

In either case, I think what you're looking for is:

select count(distinct source_id) from obis_sources;

Michael Glaesemann
grzm seespotcode net