(Created page with "<tab sep=bar head=top class=diff> '''Primary Key''' | '''Unique''' A primary key is a constraint that ensures that a fi...") |
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Revision as of 16:41, 3 March 2015
| Primary Key | Unique |
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| A primary key is a constraint that ensures that a field or column of a sql table does not hold duplicate or null values | Unique is a constraint that a field does not have duplicates but allows null values. |
| There can be only one primary key in a sql table | A Unique constraint can be applied on more than one field. |