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Which of the following is true about a primary key constraint in SQL?
- a)It allows null values in the column.
- b)It allows duplicate values in the column.
- c)It uniquely identifies a row in a table.
- d)It is not required for every table.
Correct answer is option 'C'. Can you explain this answer?
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Which of the following is true about a primary key constraint in SQL?a...
A primary key constraint in SQL ensures that the values in the specified column(s) uniquely identify each row in the table.
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Which of the following is true about a primary key constraint in SQL?a...
Primary Key Constraint in SQL
Uniquely identifies a row in a table:
A primary key constraint in SQL ensures that each row in a table is uniquely identified by the values in the specified column(s). This means that no two rows can have the same value for the primary key column(s), making it a crucial component for data integrity and uniqueness.
Does not allow null values in the column:
Another important characteristic of a primary key constraint is that it does not allow null values in the column(s) it is applied to. This ensures that the primary key values are always present and can be used to uniquely identify each row in the table.
Does not allow duplicate values in the column:
In addition to not allowing null values, a primary key constraint also ensures that duplicate values are not allowed in the column(s) it is applied to. This enforces the uniqueness requirement of the primary key and helps maintain data integrity.
Required for every table:
While a primary key constraint is not technically required for every table, it is considered a best practice to have a primary key defined for each table. This helps in establishing relationships between tables, ensuring data integrity, and improving query performance.
In conclusion, a primary key constraint in SQL uniquely identifies a row in a table, does not allow null or duplicate values in the specified column(s), and is generally recommended for every table to maintain data integrity and relationships.
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Which of the following is true about a primary key constraint in SQL?a)It allows null values in the column.b)It allows duplicate values in the column.c)It uniquely identifies a row in a table.d)It is not required for every table.Correct answer is option 'C'. Can you explain this answer?
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