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what is primary key,unique key, foreign key? can u teach me
in simple language?
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Answer Posted / sriniwaas41
dublicate values- means two same values not allowed
primary key:does not allow null values and does not allow
dublicate v
alues
-reapeated values and null values not allowed
-we can use primary key only once in a table
unique key:
-reapeated values not allowed as per primary key.
-but the difference is null values are allowed
-another difference is we can declare more thatn one
unique column in a table.primary is not allowed
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