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zhshqzyc
Posting Yak Master
240 Posts |
 Posted - 2013-03-08 : 13:46:37
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http://www.w3schools.com/sql/sql_foreignkey.aspTo create a FOREIGN KEY constraint on the "P_Id" column when the "Orders" table is already created, use the following SQL:ALTER TABLE OrdersADD FOREIGN KEY (P_Id)REFERENCES Persons(P_Id) To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax:ALTER TABLE OrdersADD CONSTRAINT fk_PerOrdersFOREIGN KEY (P_Id)REFERENCES Persons(P_Id) One has the keyword "constraint", the other no.I can't figure it out the difference.I think that the first one is enough for the normal query. |
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Bustaz Kool
Master Smack Fu Yak Hacker
1834 Posts |
Posted - 2013-03-08 : 19:38:56
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| Question: Do you want to define the name of the constraint? (Hint: You do!)Use the syntax that allows you to do what you want. Also, it is common practice to also define an index on the foreign key column(s) for performance purposes. You may already have this in place or your tables may be too small to warrant it.=================================================There are two kinds of light -- the glow that illuminates, and the glare that obscures. -James Thurber |
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visakh16
Very Important crosS Applying yaK Herder
52326 Posts |
Posted - 2013-03-09 : 00:55:34
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| defining it as a constraint makes it easier to identify it later------------------------------------------------------------------------------------------------------SQL Server MVPhttp://visakhm.blogspot.com/ |
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About Foreign Key Constraint