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gautham.gn
Starting Member
19 Posts |
 Posted - 2013-12-02 : 13:15:20
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| There is a restriction that we must have only one primary key per table. We can have composite primary key by defining primary key over 2 or more columns. Actually,, a primary key uniquely defines the table and if we have two or more columns which follow unique and not null features why can't we have two primary keys?? I want to know what is the main reason behind having only one primary key in a table?? |
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tkizer
Almighty SQL Goddess
38200 Posts |
Posted - 2013-12-02 : 13:56:19
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| Just add a unique index/constraint if you need to define more than one.Tara KizerSQL Server MVP since 2007http://weblogs.sqlteam.com/tarad/ |
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gautham.gn
Starting Member
19 Posts |
Posted - 2013-12-02 : 21:23:30
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| I know that I can add one more unique constraint on a column but I want the reason why there is a restriction that a table should have only one primary key?? Why not 2 or more?? |
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Lamprey
Master Smack Fu Yak Hacker
4614 Posts |
Posted - 2013-12-03 : 12:11:41
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| SQL Server only allows one primary key. It's like having two children and saying they are both first born; It doesn't make sense. In reality a PK is only a unique constraint on a non-nullable column, but it has the special distinction on being "primary." Additionally, people tend to associate the clustering of a table on the primary key, although that is not a requirement for a PK. |
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Primary key