Answer / nashiinformaticssolutions

• Primary Key:
o Ensures each row in a table is unique.
o Cannot contain NULL values.
o A table can have only one primary key.
• Unique Key:
o Ensures all values in a column are unique.
o Can contain a single NULL value.
o A table can have multiple unique keys.

Answer / glibwaresoftsolutions

• Primary Key:
o Ensures each row in a table is unique.
o Cannot contain NULL values.
o A table can have only one primary key.
• Unique Key:
o Ensures all values in a column are unique.
o Can contain a single NULL value.
o A table can have multiple unique keys.

Answer / hr@tgksolutions.com

• Primary Key:
o Ensures each row in a table is unique.
o Cannot contain NULL values.
o A table can have only one primary key.
• Unique Key:
o Ensures all values in a column are unique.
o Can contain a single NULL value.
o A table can have multiple unique keys.

Create table emp (id number(9), name varchar2(20),salary number(9,2)); The table has 100 records after table created.Now i nee to change id's Datatype is to be Varchar2(15). now Alter table emp modify(id varchar2(15),name varchar2(20), salary number(9,2)); Whether it will work or returns error? post answer with explanation.

13 Answers   Oracle, TCS,

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