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MySQL Interview Questions

What is the purpose of the 'HAVING' clause?

  • A) To filter records after aggregation has been performed.
  • B) To sort the result set.
  • C) To create a new table.
  • D) To update existing records.
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Correct Answer: A - To filter records after aggregation has been performed.

What does the 'INDEX' keyword do in MySQL?

  • A) It creates a backup of the database.
  • B) It improves the speed of data retrieval operations.
  • C) It deletes records from a table.
  • D) It defines a new table structure.
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Correct Answer: B - It improves the speed of data retrieval operations.

What are stored procedures in MySQL?

  • A) A way to store data permanently.
  • B) A set of SQL statements that can be stored and reused.
  • C) A method to optimize database performance.
  • D) A way to create indexes.
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Correct Answer: B - A set of SQL statements that can be stored and reused.

What does the 'CRUD' acronym stand for in database operations?

  • A) Create, Read, Update, Delete.
  • B) Create, Retrieve, Update, Drop.
  • C) Create, Read, Upload, Delete.
  • D) Create, Read, Update, Design.
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Correct Answer: A - Create, Read, Update, Delete.

What is the difference between 'INNER JOIN' and 'LEFT JOIN' in MySQL?

  • A) INNER JOIN returns all records from both tables.
  • B) LEFT JOIN returns all records from the left table and matched records from the right table.
  • C) INNER JOIN returns all records from the left table regardless of matches.
  • D) LEFT JOIN is faster than INNER JOIN.
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Correct Answer: B - LEFT JOIN returns all records from the left table and matched records from the right table.

What is the purpose of the 'HAVING' clause in MySQL?

  • A) To filter records before grouping.
  • B) To filter records after grouping.
  • C) To sort records in descending order.
  • D) To join multiple tables.
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Correct Answer: B - To filter records after grouping.

What is the significance of the 'AUTO_INCREMENT' attribute in MySQL?

  • A) It automatically generates a unique value for a column when a new record is inserted.
  • B) It allows a column to accept null values.
  • C) It ensures that a column can only contain unique values.
  • D) It is used to create foreign keys.
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Correct Answer: A - It automatically generates a unique value for a column when a new record is inserted.

What does the 'GROUP BY' clause do in a SQL query?

  • A) It groups rows that have the same values in specified columns into summary rows.
  • B) It orders the result set by a specified column.
  • C) It filters records based on a specified condition.
  • D) It combines multiple tables into one.
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Correct Answer: A - It groups rows that have the same values in specified columns into summary rows.

What does the 'LIMIT' clause do in a SQL query?

  • A) It restricts the number of rows returned by the query.
  • B) It sorts the result set in a specific order.
  • C) It filters records based on a specified condition.
  • D) It groups rows that have the same values.
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Correct Answer: A - It restricts the number of rows returned by the query.

What is the function of the 'INDEX' in MySQL?

  • A) To speed up the retrieval of rows from a table.
  • B) To enforce data integrity.
  • C) To create a backup of the database.
  • D) To delete records from a table.
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Correct Answer: A - To speed up the retrieval of rows from a table.

What is the difference between 'CHAR' and 'VARCHAR' data types in MySQL?

  • A) CHAR is fixed-length, while VARCHAR is variable-length.
  • B) CHAR can store more data than VARCHAR.
  • C) VARCHAR is faster than CHAR.
  • D) CHAR is used for numeric data, while VARCHAR is for text.
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Correct Answer: A - CHAR is fixed-length, while VARCHAR is variable-length.