COMPUTER SCIENCE AND ENGINEERING
SQL
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Which of the following command is the correct syntax for adding primary key constraint in existing table?
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ALTER TABLE <tableName> ADD CONSTRAINT <constraintName> PRIMARY KEY(columnName);
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ALTER TABLE <tableName> ADD CONSTRAINT PRIMARY KEY(columnName);
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ALTER TABLE <tableName> ADD CONSTRAINT <columnName> PRIMARY KEY;
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None of these
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Explanation:
Detailed explanation-1: -The basic syntax of ADD CONSTRAINT is: ALTER TABLE table name ADD CONSTRAINT PRIMARY KEY (col1, col2); The above command would add a primary key constraint to the table table name .
Detailed explanation-2: -Add Primary key to the Existing Table. If you want to add a primary key in the existing table, you have to use the following ALTER syntax in SQL: ALTER TABLE Table Name ADD CONSTRAINT Constraint Name PRIMARY KEY (Column Name);
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