COMPUTER SCIENCE AND ENGINEERING
SQL
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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CHECK
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PRIMARY KEY
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UNIQUE
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NOT NULL
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FOREIGN KEY
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Detailed explanation-1: -The NOT NULL constraint is used to ensure that a given column of a table is never assigned the null value. Once a NOT NULL constraint has been defined for a particular column, any insert or update operation that attempts to place a null value in that column will fail.
Detailed explanation-2: -Primary key constraints ALTER TABLE ADD PRIMARY KEY allows you to include existing columns in a primary key if they were first defined as NOT NULL. NULL values are not allowed. If the column(s) contain NULL values, the system will not add the primary key constraint. See ALTER TABLE statement for more information.
Detailed explanation-3: -NOT NULL Constraint − Ensures that a column cannot have NULL value. DEFAULT Constraint − Provides a default value for a column when none is specified. UNIQUE Constraint − Ensures that all values in a column are different. PRIMARY Key − Uniquely identifies each row/record in a database table.