1. What is a SQL JOIN?
Explanation: A SQL JOIN is used to combine data from multiple tables into a single result set.
Report for correction2. Which type of JOIN returns only the common rows between two tables?
Explanation: An INNER JOIN returns only the rows that have matching values in both tables being joined.
Report for correction3. What is a self-join?
Explanation: A self-join is a join where a table is joined with itself, typically using aliases to distinguish between the two instances of the same table.
Report for correction4. Which SQL JOIN returns all rows from the left table and the matched rows from the right table?
Explanation: A LEFT JOIN returns all rows from the left table and the matched rows from the right table. If there are no matches, NULL values are returned for the right table's columns.
Report for correction5. What is a subquery in SQL?
Explanation: A subquery is a query that is embedded inside another query and is used to retrieve data for further processing.
Report for correction6. Which SQL operator is used to compare a subquery result to a single value?
Explanation: The IN operator is used to compare a subquery result to a set of values, and it returns rows that match any value in the set.
Report for correction7. What does the SQL EXISTS operator do?
Explanation: The EXISTS operator is used to check if a subquery returns any rows. It returns TRUE if the subquery result is not empty.
Report for correction8. Which type of subquery returns multiple rows of data?
Explanation: A non-correlated subquery returns multiple rows of data and is independent of the outer query.
Report for correction9. What is a correlated subquery in SQL?
Explanation: A correlated subquery is a subquery that references columns from the outer query, allowing it to be dependent on the outer query.
Report for correction10. What is the purpose of the SQL UNION operator?
Explanation: The UNION operator is used to combine rows from two or more SELECT statements or tables into a single result set.
Report for correction11. Which SQL JOIN returns all rows from both tables, with NULL values in columns where there is no match?
Explanation: A FULL OUTER JOIN returns all rows from both tables and includes NULL values in columns where there is no match.
Report for correction12. What is the purpose of the SQL INTERSECT operator?
Explanation: The INTERSECT operator is used to retrieve rows that are common to two result sets.
Report for correction13. What does the SQL HAVING clause do?
Explanation: The HAVING clause is used to filter rows after grouping has been performed, typically in combination with the GROUP BY clause.
Report for correction14. Which SQL JOIN returns all rows from the right table and the matched rows from the left table?
Explanation: A RIGHT JOIN returns all rows from the right table and the matched rows from the left table. If there are no matches, NULL values are returned for the left table's columns.
Report for correction15. What is the purpose of the SQL UNION ALL operator?
Explanation: The UNION ALL operator is used to combine rows from two or more SELECT statements, including duplicate rows.
Report for correction16. Which SQL operator is used to filter rows based on a pattern match in a text column?
Explanation: The LIKE operator is used to filter rows based on a pattern match in a text column using wildcard characters.
Report for correction17. What is the purpose of the SQL EXCEPT operator?
Explanation: The EXCEPT operator is used to retrieve rows that are in the first result set but not in the second result set.
Report for correction18. What is the primary difference between UNION and UNION ALL in SQL?
Explanation: The primary difference is that UNION removes duplicate rows from the combined result set, while UNION ALL includes all rows, including duplicates.
Report for correction19. In SQL, what does the JOIN condition specify?
Explanation: The JOIN condition specifies the criteria for matching rows from different tables in a SQL join operation.
Report for correction20. What is the purpose of the SQL GROUP BY clause?
Explanation: The GROUP BY clause is used to group rows based on one or more columns and apply aggregate functions to the grouped data.
Report for correction21. Which SQL operator is used to specify a range of values in a WHERE clause?
Explanation: The BETWEEN operator is used to specify a range of values in a WHERE clause.
Report for correction22. In SQL, what is a subquery used for?
Explanation: A subquery is used to retrieve data for use in another query, often as a condition for filtering or matching rows.
Report for correction23. What does the SQL ORDER BY clause do?
Explanation: The ORDER BY clause is used to specify the order in which rows should be displayed in the result set.
Report for correction24. What is the purpose of the SQL DISTINCT keyword?
Explanation: The DISTINCT keyword is used to retrieve unique (distinct) values from a column in the result set.
Report for correction25. In SQL, what does the JOIN ON clause specify?
Explanation: The JOIN ON clause specifies the criteria for matching rows from different tables in a SQL join operation.
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