Both keys ensure that a column or a combination of columns in a table or relation is unique. The primary key identifies each record in the table, whereas the unique key, with the exception of NULL values, prevents duplicate entries in a field.
The UNIQUE constraint assures that each column's values are unique. The UNIQUE and PRIMARY KEY constraints both guarantee that a column or collection of columns is unique. A UNIQUE constraint is immediately added to a PRIMARY KEY constraint.
A group of one or more table fields/columns that uniquely identify a record in a database table is known as a unique key. It's similar to a primary key in that it can only accept one null value and cannot have duplicate values.
A group of one or more fields/columns in a table that uniquely identify a record in a database table is known as a unique key. It's similar to a primary key in that it accepts just one null value and cannot have duplicate values.
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Umesh Wankhede
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Monesh Ram
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Well Explained in Every Chapters..
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GAJANAN DIGAMBAR MODE
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very easy to understand SQL its was dream to learn SQL. Thanx for Learnvern
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NAGASWETHA
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very useful
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mohd aamir
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Hi Team,
Why you didn't teach/learn how to write select query, even you shared 15 question for practice :(
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Yashvant Kadwe
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I have found the course to be interesting with plenty of valuable information provided as part of the course and through interaction with fellow teachers and trainers from a wide range of disciplines
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