Обсуждение: Docs claim that "select myTable.*" wildcard won't let you assign column names
<div style="font-family: Verdana;font-size: 12.0px;"><div> </div><div>From http://www.postgresql.org/docs/9.4/static/sql-select.html(and previous version too):</div><div><h3><tt class="COMMAND"> ##SELECT</tt> List</h3><div> <...></div></div><div> Instead of an expression, <tt class="LITERAL">*</tt>can be written in the output list as a shorthand for all the columns of the selected rows.</div><div> Also, you can write <tt class="LITERAL"><tt class="REPLACEABLE c2">table_name</tt>.*</tt> as a shorthandfor the columns coming from just that table. In these cases it is not</div><div> possible to specify new nameswith <tt class="LITERAL">AS</tt>; the output column names will be the same as the table columns' names.</div><div> </div><div>But, thedocs elsewhere feature a query example show the use of a wildcard for columns</div><div>aswell as allowing you to assign names to as many of the leading columns as you wish:</div><div> <div><div>WITHT0 as ( SELECT 1,2,3 )<br /> SELECT T0.* from T0 as T0(foo,bar) ;</div><div> </div><div><div> foo │ bar │ ?column?<br/> ─────┼─────┼──────────<br /> 1 │ 2 │ 3<br /> (1 row)</div><div> </div><div>The following curiousvariant also works:</div><div> </div><div>WITH T0 as ( SELECT 1,2,3 )<br /> SELECT justAnythingReally.* from T0 asjustAnythingReally(foo,bar) ;</div></div> <div>The synoposis/grammer at the top doesn't hint at this either. I've checkedand this has been supported since at least 9.2 .</div><div> </div><div>Regards,</div><div>Amir</div><div> </div></div></div></div>
Re: Docs claim that "select myTable.*" wildcard won't let you assign column names
От
"David G. Johnston"
Дата:
On Monday, September 21, 2015, Amir Rohan <amir.rohan@mail.com> wrote:
From http://www.postgresql.org/docs/9.4/static/sql-select.html (and previous version too):##SELECT List
<...>Instead of an expression, * can be written in the output list as a shorthand for all the columns of the selected rows.Also, you can write table_name.* as a shorthand for the columns coming from just that table. In these cases it is notpossible to specify new names with AS; the output column names will be the same as the table columns' names.But, the docs elsewhere feature a query example show the use of a wildcard for columnsas well as allowing you to assign names to as many of the leading columns as you wish:WITH T0 as ( SELECT 1,2,3 )
SELECT T0.* from T0 as T0(foo,bar) ;foo │ bar │ ?column?
─────┼─────┼──────────
1 │ 2 │ 3
(1 row)The following curious variant also works:WITH T0 as ( SELECT 1,2,3 )
SELECT justAnythingReally.* from T0 as justAnythingReally(foo,bar) ;The synoposis/grammer at the top doesn't hint at this either. I've checked and this has been supported since at least 9.2 .
Neither of those examples is:
SELECT * AS "how would one alias this?" FROM table
So what's your point? Obviously you can alias stuff before it makes its way into a select-list that refers to it using *
In this case the FROM clause is what is being alised. It is documented though I'd need to look to identify the specific location. It would not be documented in a section regarding the select-list.
David J.
Re: Docs claim that "select myTable.*" wildcard won't let you assign column names
От
"Amir Rohan"
Дата:
On Monday, September 21, 2015, Amir Rohan <amir.rohan@mail.com> wrote: >> From http://www.postgresql.org/docs/9.4/static/sql-select.html[http://www.postgresql.org/docs/9.4/static/sql->> select.html](and previous version too): >> >> ##SELECT List >> >> <...> >> Instead of an expression, * can be written in the output list as a shorthand for all the columns of the >> selected rows. >> Also, you can write table_name.* as a shorthand for the columns coming from just that table. In these >> cases it is not possible to specify new names with AS; the output column names will be the same as the >> table columns' names. >> >> But, the docs elsewhere feature a query example show the use of a wildcard for columns >> as well as allowing you to assign names to as many of the leading columns as you wish: >> >> >> WITH T0 as ( SELECT 1,2,3 ) >> SELECT T0.* from T0 as T0(foo,bar) ;<...> On Monday, September 21, 2015, David G. Johnston wrote: > Neither of those examples is: > > SELECT * AS "how would one alias this?" FROM table > > So what's your point? My point is that "In these cases it is not possible to specify new names with AS" is misleading because it *is* possible and useful, but requires syntax which isn't clearly shown (if at all) where I'd expect it. I think that could be improved. > Obviously you can alias stuff before it makes its way into a select-list that refers to it using * "obvious" to whom? probably not to someone who's level of SQL mastery has brought him/her to reading the exciting "SELECT" documentation. I do see your point though, in the grammar the "AS" in my example belongs not to `output_name ` but to `from_item`. So this syntax is hidden away behind the `column_alias` production. > In this case the FROM clause is what is being aliased. It is documented though I'd need to look to > identify the specific location. This belongs in the page describing SELECT, and though I've looked I haven't found it. If I'm wrong ( I did look again just now), please correct me. Amir
On 09/21/2015 06:04 PM, Amir Rohan wrote: > This belongs in the page describing SELECT, and though I've looked I haven't found it. If I'm wrong ( > I did look again just now), please correct me. Feel free to submit a doc patch if you feel it needs to be improved, but it is mentioned here: http://www.postgresql.org/docs/9.4/interactive/sql-select.html#SQL-FROM 8<----------- alias A substitute name for the FROM item [...] If an alias is written, a column alias list can also be written to provide substitute names for one or more columns of the table. 8<----------- Joe -- Crunchy Data - http://crunchydata.com PostgreSQL Support for Secure Enterprises Consulting, Training, & Open Source Development
Вложения
Re: Docs claim that "select myTable.*" wildcard won't let you assign column names
От
"David G. Johnston"
Дата:
On Monday, September 21, 2015, Amir Rohan <amir.rohan@mail.com> wrote:
The docs don't make a big deal of alising other than noting individually where they can happen (cte, from clause, select-list) and few questions that are raised are probably better served to be simply handled on these lists than cluttering the docs.
On Monday, September 21, 2015, Amir Rohan <amir.rohan@mail.com> wrote:
>> From http://www.postgresql.org/docs/9.4/static/sql-select.html[http://www.postgresql.org/docs/9.4/static/sql->> select.html] (and previous version too):
>>
>> ##SELECT List
>>
>> <...>
>> Instead of an expression, * can be written in the output list as a shorthand for all the columns of the
>> selected rows.
>> Also, you can write table_name.* as a shorthand for the columns coming from just that table. In these
>> cases it is not possible to specify new names with AS; the output column names will be the same as the
>> table columns' names.
>>
>> But, the docs elsewhere feature a query example show the use of a wildcard for columns
>> as well as allowing you to assign names to as many of the leading columns as you wish:
>>
>>
>> WITH T0 as ( SELECT 1,2,3 )
>> SELECT T0.* from T0 as T0(foo,bar) ;<...>
On Monday, September 21, 2015, David G. Johnston wrote:
> Neither of those examples is:
>
> SELECT * AS "how would one alias this?" FROM table
>
> So what's your point?
My point is that "In these cases it is not possible to specify new names with AS" is misleading because
it *is* possible and useful, but requires syntax which isn't clearly shown (if at all) where I'd expect it.
I think that could be improved.
> Obviously you can alias stuff before it makes its way into a select-list that refers to it using *
"obvious" to whom? probably not to someone who's level of SQL mastery has brought him/her to reading
the exciting "SELECT" documentation. I do see your point though, in the grammar the "AS" in my example
belongs not to `output_name ` but to `from_item`. So this syntax is hidden away behind the `column_alias`
production.
> In this case the FROM clause is what is being aliased. It is documented though I'd need to look to
> identify the specific location.
This belongs in the page describing SELECT, and though I've looked I haven't found it. If I'm wrong (
I did look again just now), please correct me.
To be honest, if you have a situation where you think you need to alias "*" you should probably be expanding that "*" out into individual column names anyway, which you can easily alias.
David J.
Re: Docs claim that "select myTable.*" wildcard won't let you assign column names
От
"Amir Rohan"
Дата:
On Monday, September 21, 2015, David G. Johnston wrote: >To be honest, if you have a situation where you think you need to alias "*" >you should probably be expanding that "*" out into individual column names >anyway, which you can easily alias. > That depends. If my table has 30 columns and I just need to rename the first couple, then I probably would find that advice unreasonable. >The docs don't make a big deal of alising other than noting individually >where they can happen (cte, from clause, select-list) and few questions >that are raised are probably better served to be simply handled on these >lists than cluttering the docs. What constitutes "clutter", or what is "obvious", really depends on who is making the assertion. A pg veteran's views probably don't mirrort those of the person you'd typically find actually reading the docs, trying to figure out how to write the query they want. But yeah, the pg documentation isn't the best resource to pick up SQL from (nor is is their purpose), and no patch I'd submit would really change that. So, we're done. Amir