BUG #7899: allow key word as alias in subquery but Can't reference it in outer query

[Jov]

The following bug has been logged on the website:

Bug reference: 7899
Logged by: jov
Email address: ***@amutu.com
PostgreSQL version: 9.1.3
Operating system: CentOS 6
Description:

xxx=# select 2 from (select 1 as end) t;
?column?
----------
2
(1 row)

xxx=# select end from (select 1 as end) t;
ERROR: syntax error at or near "end"
LINE 1: select end from (select 1 as end) t;
^

xxx=# select version();
version


------------------------------------------------------------------------------------------------------------

[Tom Lane]

Post by Jov
xxx=# select end from (select 1 as end) t;
ERROR: syntax error at or near "end"
LINE 1: select end from (select 1 as end) t;
^

You need to double-quote the outer use of "end", viz

regression=# select "end" from (select 1 as end) t;
end
-----
1
(1 row)

In the context with "as", Postgres can tell the word is meant as a
column identifier not a keyword, but there's no way for it to know that
in the outer usage.

Post by Jov
I think use key word as alias should get a error message such as $key_word
is Key Word,should not be used as identifier bla bla,so for some complex
query error user can save a lot of time.

Well, yours is the first complaint we've ever had in that direction,
whereas we used to get a lot of complaints in the opposite direction,
back when we didn't allow keywords to be used for column names.
So I doubt we'll change it. It is an interesting gotcha though :-(

regards, tom lane

[Jov]

I have get the description of this behaviour from doc 7.3.2
http://www.postgresql.org/docs/devel/static/queries-select-lists.html#QUERIES-COLUMN-LABELS
.

from the error message now,I think syntax error may emmit by the
parser,parser error make it hard to get the really condition such as the
second token ‘end’ is a select item from a select statement.

thanks

Post by Tom Lane

Post by Jov
xxx=# select end from (select 1 as end) t;
ERROR: syntax error at or near "end"
LINE 1: select end from (select 1 as end) t;
^

You need to double-quote the outer use of "end", viz
regression=# select "end" from (select 1 as end) t;
end
-----
1
(1 row)
In the context with "as", Postgres can tell the word is meant as a
column identifier not a keyword, but there's no way for it to know that
in the outer usage.

Post by Jov
I think use key word as alias should get a error message such as

$key_word

Post by Jov
is Key Word,should not be used as identifier bla bla,so for some complex
query error user can save a lot of time.

Well, yours is the first complaint we've ever had in that direction,
whereas we used to get a lot of complaints in the opposite direction,
back when we didn't allow keywords to be used for column names.
So I doubt we'll change it. It is an interesting gotcha though :-(
regards, tom lane
.

[Jov]

can we make a cross reference from doc 4.4.1(
http://www.postgresql.org/docs/devel/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
)
to
doc 7.3.2 (
http://www.postgresql.org/docs/devel/static/queries-select-lists.html#QUERIES-COLUMN-LABELS
)
*to mention that “AS” can make a key word to be a identifier?*
I have read the doc 4.4.1 and can't find this info from there so I thin it
is a bug.

Post by Jov
I have get the description of this behaviour from doc 7.3.2
http://www.postgresql.org/docs/devel/static/queries-select-lists.html#QUERIES-COLUMN-LABELS
.
from the error message now,I think syntax error may emmit by the
parser,parser error make it hard to get the really condition such as the
second token ‘end’ is a select item from a select statement.
thanks

Post by Tom Lane

Post by Jov
xxx=# select end from (select 1 as end) t;
ERROR: syntax error at or near "end"
LINE 1: select end from (select 1 as end) t;
^

You need to double-quote the outer use of "end", viz
regression=# select "end" from (select 1 as end) t;
end
-----
1
(1 row)
In the context with "as", Postgres can tell the word is meant as a
column identifier not a keyword, but there's no way for it to know that
in the outer usage.

Post by Jov
I think use key word as alias should get a error message such as

$key_word

Post by Jov
is Key Word,should not be used as identifier bla bla,so for some complex
query error user can save a lot of time.

Well, yours is the first complaint we've ever had in that direction,
whereas we used to get a lot of complaints in the opposite direction,
back when we didn't allow keywords to be used for column names.
So I doubt we'll change it. It is an interesting gotcha though :-(
regards, tom lane
.

--
Jov
blog: http:amutu.com/blog <http://amutu.com/blog>