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j0shua
Starting Member
40 Posts |
 Posted - 2009-03-25 : 05:39:01
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| Hi there, i have been assigned to an existing database that is being used in a software. I check the tables and found out that there are tables whose relationship is not based on foreign keys and primary keys. The tables are connected through a common field. What is the effect of this in the long run? how can i edit this safely without any side effect on the current database? thank you. help is very much appreciated. |
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RickD
Slow But Sure Yak Herding Master
3608 Posts |
Posted - 2009-03-25 : 06:50:23
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| Does every row join between the tables? Are there nulls on either side?There are lots of fields in databases that are logically foreign keys, but can't be created as such due to reasons like nullability.If there are no nulls, you can create a foreign key as long as you're 100% sure it is a true foreign key. |
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j0shua
Starting Member
40 Posts |
Posted - 2009-03-25 : 07:11:38
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| thank you. is the foreign key must be a primary key on the other table? |
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RickD
Slow But Sure Yak Herding Master
3608 Posts |
Posted - 2009-03-25 : 09:14:50
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| Yes, it must always exist as a primary key on another table. |
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robvolk
Most Valuable Yak
15732 Posts |
Posted - 2009-03-25 : 12:45:16
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| Technically it just needs to have a unique constraint, it doesn't have to be the primary key. |
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Tables Relationship