Question { TCS, 174431 }

what is primary key,unique key, foreign key? can u teach me
in simple language?

Answer

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