Re: SQL3 UNDER
От | Robert B. Easter |
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Тема | Re: SQL3 UNDER |
Дата | |
Msg-id | 00052303541902.00239@comptechnews обсуждение исходный текст |
Ответ на | Re: SQL3 UNDER (Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>) |
Список | pgsql-hackers |
On Tue, 23 May 2000, Chris Bitmead wrote: > If you think the semantics are different provide a specific example > (including SQL) of how you think their behaviour is different - that is > how you think UNDER should work differently to current INHERIT. > I'll try to provide examples later. For now, did you see the gif attachments on a earlier message of mine? The UNDER and CLONES/INHERITS gif pictures provide a graphical view of what I mean. UNDER creates tree hierarchy down vertically, while INHERITS supports multiple inheritance in a lateral direction. The UNDER trees can be under any table that is part of an INHERITS relationship. UNDER and INHERITS work at different levels sorta. A subtable in an UNDER hierarchy can't be in an INHERITS clause because it is logically just part of its maximal supertable. In other words, INHERITS can provide a relationship between different whole trees created by UNDER, by way of a maximal supertable being inherited by another maximal supertable with its own UNDER tree. Make any sense? :-) -- Robert B. Easter reaster@comptechnews.com
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