SQL Primary Key
1.What will happen?
CREATE TABLE students (
id INT PRIMARY KEY,
name VARCHAR(50)
);
INSERT INTO students VALUES (1, 'Alice');
INSERT INTO students VALUES (1, 'Bob');
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A. Both rows inserted
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B. Second insert overwrites
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C. Error due to duplicate PRIMARY KEY
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D. Table auto-increments
Error due to duplicate PRIMARY KEY
Error due to duplicate PRIMARY KEY
2.What will be the Output?
CREATE TABLE test (
id INT,
name VARCHAR(20),
PRIMARY KEY (id)
);
INSERT INTO test VALUES (NULL, 'Ravi');
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A. NULL inserted
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B. Error: NULL not allowed in PRIMARY KEY
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C. Default value is assigned
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D. Column is auto-generated
Error: NULL not allowed in PRIMARY KEY
Error: NULL not allowed in PRIMARY KEY
3.What is a PRIMARY KEY used for?
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A. To create indexes
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B. To allow duplicate rows
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C. To uniquely identify records
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D. To auto-increment columns
To uniquely identify records
To uniquely identify records
4.Can a table have more than one PRIMARY KEY?
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A. Yes
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B. No
No
No
5.Which of the following is true about PRIMARY KEY?
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A. Allows NULL values
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B. Allows duplicates
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C. Combines NOT NULL + UNIQUE
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D. Has no constraints
Combines NOT NULL + UNIQUE
Combines NOT NULL + UNIQUE