Thread: How do I extract ONE particular field, when multiple table contain the same field name?

Hi,

I am pretty new att using SQL-quires, could anyone help me with this
one:

I want to do the following SQL-query:

Select XID, DENOM, PRICE, FRT, CTID From XItem xi, Category c Where
xi.System=1 and xi.Category=c.Index

the problem is that the field 'DENOM' is present in both table 'XItem'
and
'Category' (it is a text description field where you explain whatever
you
want). Therefore I get the following complaint when I run the query:
Error msg: "The specified fiel 'DENOM' could refer to more than one
table listed
in the FROM clause of your SQL-statement"

The DENOM-field I actually want is the one belonging to the
XItem-table.
I would most appreciate if someone could give me a hint how to alter
the
SELECT-statement above so that it does what I want.

Regards

/olw

olle.wijk@systecon.se (Olle Wijk) wrote in message news:<6baa8767.0109120106.67f94cf5@posting.google.com>...
> Hi,
> 
> I am pretty new att using SQL-quires, could anyone help me with this
> one:
> 
> I want to do the following SQL-query:
> 
> Select XID, DENOM, PRICE, FRT, CTID From XItem xi, Category c Where
> xi.System=1 and xi.Category=c.Index
> 
> the problem is that the field 'DENOM' is present in both table 'XItem'
> and
> 'Category' (it is a text description field where you explain whatever
> you
> want). Therefore I get the following complaint when I run the query:
>  
> Error msg: "The specified fiel 'DENOM' could refer to more than one
> table listed
> in the FROM clause of your SQL-statement"
> 
> The DENOM-field I actually want is the one belonging to the
> XItem-table.
> I would most appreciate if someone could give me a hint how to alter
> the
> SELECT-statement above so that it does what I want.
> 
> Regards
> 
> /olw


When joinning tables, as you did, it's hardly recommended using
aliases, as you did too. (XItem <=> xi and Category <=> c). These
aliases can be used in all the SELECT statement including WHERE
clause, as you did again :), and SELECT clause. So, to refer to the
DENOM field from the table XItem, you should write :
xi.DENOM instead of DENOM alone. Your SELECT statement will be :
Select XID, xi.DENOM, PRICE, FRT, CTID From XItem xi, Category c
Wherexi.System=1 and xi.Category=c.Index

Notice than if you don't want to use aliases (what a wrong idea !),
you can write like the following :
Select XID, XItem.DENOM, PRICE, FRT, CTID From XItem, Category WhereXItem.System=1 and XItem.Category=Category.Index

Just some remarks about writing SQL statement.
it's preferabled (in my point of view) to :- write key words (like SELECT, FROM, WHERE, ...) in upper case- go to the
nextline when you change of key word- always use aliases- keep always the same alias for the same table in all the
queries-write the fields in lower case- write the first lettre of a table name in upper, the rest in lower
 
case- use a "_ID" suffixe to the field name when it correspond to the
primary key of another table- name "ID" the primary key of a table

I would write your sql statement like :
SELECT xi.ID, xi.denom, xi.price, xi.frt, cat.ID FROM XItem AS xi, Category AS catWHERE xi.system = 1 AND
xi.category_ID= cat.ID;
 

good luck
Yoann

You need to qualify "DENOM" with the table name: just write "xi.DENOM".
I find this to be good general practice when selecting from more than one
table.

----- Original Message -----
From: "Olle Wijk" <olle.wijk@systecon.se>
To: <pgsql-sql@postgresql.org>
Sent: Wednesday, September 12, 2001 4:06 AM
Subject: How do I extract ONE particular field, when multiple table contain
the same field name?


> Hi,
>
> I am pretty new att using SQL-quires, could anyone help me with this
> one:
>
> I want to do the following SQL-query:
>
> Select XID, DENOM, PRICE, FRT, CTID From XItem xi, Category c Where
> xi.System=1 and xi.Category=c.Index
>
> the problem is that the field 'DENOM' is present in both table 'XItem'
> and
> 'Category' (it is a text description field where you explain whatever
> you
> want). Therefore I get the following complaint when I run the query:
>
> Error msg: "The specified fiel 'DENOM' could refer to more than one
> table listed
> in the FROM clause of your SQL-statement"
>
> The DENOM-field I actually want is the one belonging to the
> XItem-table.
> I would most appreciate if someone could give me a hint how to alter
> the
> SELECT-statement above so that it does what I want.
>
> Regards
>
> /olw
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster
>
>

What you want to know is probably this:

Select XID, xi.DENOM, PRICE, FRT, CTID From XItem xi, Category c Wherexi.System=1 and xi.Category=c.Index

Regards,
Patrik Kudo

On Wednesday, 12. September 2001 11:06, Olle Wijk wrote:
> Hi,
>
> I am pretty new att using SQL-quires, could anyone help me with this
> one:
>
> I want to do the following SQL-query:
>
> Select XID, DENOM, PRICE, FRT, CTID From XItem xi, Category c Where
> xi.System=1 and xi.Category=c.Index
>
> the problem is that the field 'DENOM' is present in both table 'XItem'
> and 'Category' 

Just write: table.field or table-alias.field instead of just 'field' 
(like you did already in the WHERE clause):

Select XID, xi.DENOM, PRICE, FRT, CTID 
From XItem xi, Category c 
Where xi.System=1 and xi.Category=c.Index

Christof
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