(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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<tab sep=bar head=top class=diff> | <tab sep=bar head=top class=diff> | ||
'''Primary Key''' | '''Unique''' | '''Primary Key''' | '''Unique''' | ||
| − | 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. | + | 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 ensures 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. | There can be only one primary key in a sql table | A Unique constraint can be applied on more than one field. | ||
Latest revision as of 16:42, 3 March 2015
| Primary Key | Unique |
|---|---|
| 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 ensures 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. |