From: Andrew Gierth <andrew@tao11.riddles.org.uk>
To: Ian Tan <iantan1268@gmail.com>
Cc: pgsql-sql@lists.postgresql.org
Subject: Re: Help on SQL query
In-Reply-To: 
 <CAAj7RQ-vF3kPaC7Y5csgjL75Bo=FotP6W=s2LsRhirVE78b4HQ@mail.gmail.com>
	(Ian Tan's message of "Fri, 15 Feb 2019 17:22:31 +0000")
Message-ID: <87k1i1klp2.fsf@news-spur.riddles.org.uk>
References: 
 <CAAj7RQ-vF3kPaC7Y5csgjL75Bo=FotP6W=s2LsRhirVE78b4HQ@mail.gmail.com>
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Date: Fri, 15 Feb 2019 17:28:34 +0000
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>>>>> "Ian" == Ian Tan <iantan1268@gmail.com> writes:

 Ian> How do I write an SQL query so that the "name" text in car_parts
 Ian> are added to the bill_of_materials table, so that it looks like
 Ian> this:

The only trick with this is that you need to join the car_parts table
twice (once for parent and once for child), and to do that you need to
give it different alias names:

select bom.parent_id,
       ppart.name as parent_name,
       bom.child_id,
       cpart.name as child_name
  from bill_of_materials bom
  join car_parts ppart on (ppart.id=bom.parent_id)
  join car_parts cpart on (cpart.id=bom.child_id);

-- 
Andrew (irc:RhodiumToad)