From: Rob Sargent <robjsargent@gmail.com>
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Subject: Re: One parent record with 3 possible child records
Date: Thu, 2 May 2024 07:37:14 -0600
In-Reply-To: 
 <CAKFQuwYPeiXTT0GTrN3o7Ja7P9G9Z-LerHsdbzCDqe=SRhffyg@mail.gmail.com>
Cc: JORGE MALDONADO <jorgemal1960@gmail.com>
To: "David G. Johnston" <david.g.johnston@gmail.com>,
 "pgsql-sql@postgresql.org" <pgsql-sql@postgresql.org>
References: 
 <CAAY=A79usb2Lbr9nUyzxyRNWLQNc-w3oTBbtUGyC2a4E-qaX3A@mail.gmail.com>
 <CAKFQuwYPeiXTT0GTrN3o7Ja7P9G9Z-LerHsdbzCDqe=SRhffyg@mail.gmail.com>
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> On May 1, 2024, at 5:24 PM, David G. Johnston =
<david.g.johnston@gmail.com> wrote:
>=20
> On Wednesday, May 1, 2024, JORGE MALDONADO <jorgemal1960@gmail.com =
<mailto:jorgemal1960@gmail.com>> wrote:
>=20
> Let's say that tableMain has a string field called "type" with the =
following possible values: "residential", "industrial" and "energy".=20
>=20
> This, and have the same column in the other tables, but add a check =
constraint ensuring only the correct enum value can be specified.  Then =
your foreign key from the child tables to main is both the ID and the =
type field.
> =20
> David J.
Presuming the id is unique in parent and child, what=E2=80=99s the value =
of the type field in the foreign key?  Are you saying the PK on =
tableMain is (type,id), perhaps for clustering purposes?


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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html; =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;" class=3D""><br =
class=3D""><div><br class=3D""><blockquote type=3D"cite" class=3D""><div =
class=3D"">On May 1, 2024, at 5:24 PM, David G. Johnston &lt;<a =
href=3D"mailto:david.g.johnston@gmail.com" =
class=3D"">david.g.johnston@gmail.com</a>&gt; wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D"">On Wednesday, May 1, =
2024, JORGE MALDONADO &lt;<a href=3D"mailto:jorgemal1960@gmail.com" =
class=3D"">jorgemal1960@gmail.com</a>&gt; wrote:<br class=3D""><blockquote=
 class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc =
solid;padding-left:1ex"><div dir=3D"ltr" class=3D""><div dir=3D"ltr" =
class=3D""><div dir=3D"ltr" class=3D""><div class=3D""><br =
class=3D""></div><div class=3D"">Let's say that tableMain has a string =
field called "type" with the following possible values: "residential", =
"industrial" and =
"energy".&nbsp;</div></div></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">This, and have the same column in the =
other tables, but add a check constraint ensuring only the correct enum =
value can be specified.&nbsp; Then your foreign key from the child =
tables to main is both the ID and the type field.</div><div =
class=3D"">&nbsp;</div><div class=3D"">David J.</div>
</div></blockquote></div>Presuming the id is unique in parent and child, =
what=E2=80=99s the value of the type field in the foreign key? &nbsp;Are =
you saying the PK on tableMain is (type,id), perhaps for clustering =
purposes?<div class=3D""><br class=3D""></div></body></html>=

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