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Connection many to many;) Find similar branches


MVova   (2001-12-04 10:41) [0]

Who knows which way is better organized many people to many for large bases ???



Val   (2001-12-04 10:46) [1]

who organized? ;)
in essence, the question is, in general, do a table of junction between tables with a many-to-many relationship, so that there are one-to-many connections



MVova   (2001-12-04 13:24) [2]

And without the third table?
I have a few ideas, but how will be faster?
1. Duplicate entries in the detailed table but show the client one.
2. In the communication field, write a comma-separated ID of the masters and look for an entry when selecting.
My ID field is VarChar (16).



Val   (2001-12-04 13:33) [3]

In principle, you can, of course ..
1 option - what about normalization?
2 option - in theory, disappears completely, because it is not known in advance how many of them will be
and in connection with many-to-many you have a table and a master and ditale, depending on which side to watch :)



Yuvich   (2001-12-04 13:35) [4]

> MVova
Everything is allowed. But this is a violation of all the rules of the relational model. In this way, you will "tie" yourself to the system because no one wants to work with these, they will not be able to. Use the third table.



MVova   (2001-12-04 14:11) [5]

> Val
2 option - in theory, disappears completely, because it is not known in advance how many of them will be
Connection field of type Char and there 8000 imposes restrictions, but basically enough;)
> Yuvich
But this is a violation of all the rules of the relational model.
And the speed. How to quickly climb two tables or three?



Desdechado   (2001-12-04 15:42) [6]

2 MVova
is it about sampling speed? so the number of tables does not play a special role, but the volume of data retrieved in this case plays a role. If everything is normalized and indexes are built, this is fast; if it is not normalized, it is slow (duplicates are processed).
it is also necessary to take into account the amount of extracted data, since This affects the speed of transmission, especially on modem channels.

so, I recommend the classics - 3-th cross-reference table.



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Forum: "Bases";
Current archive: 2002.01.08;
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