Exploring SQL Concepts

What is the basic structure of an SQL query?

• SELECT column1, column2 FROM table_name WHERE condition;

• SELECT * FROM table_name;

• UPDATE table_name SET column1 = value1;

• INSERT INTO table_name VALUES (value1, value2);

Explain the purpose of set operations in SQL.

• Set operations are primarily for sorting data in SQL.

• Set operations only apply to single queries in SQL.

• Set operations are used to delete records from a database.

• The purpose of set operations in SQL is to combine and manipulate the results of multiple queries.

How do aggregate functions work in SQL?

• Aggregate functions only work with numeric data types.

• Aggregate functions compute a single result from a set of values, often used with GROUP BY.

• Aggregate functions return multiple results for each group.

• Aggregate functions are not compatible with JOIN operations.

What are null values in SQL and how are they handled?

• Null values in SQL are always treated as zero.

• Null values represent a default value in SQL.

• Null values can be ignored in all SQL queries.

• Null values in SQL indicate missing or unknown data and are handled using specific operators and functions.

Describe the use of nested subqueries in SQL.

• Nested subqueries are limited to a single level of depth.

• Nested subqueries cannot return multiple columns.

• Nested subqueries can only be used in SELECT statements.

• Nested subqueries are used to execute a query within another query, allowing for complex data retrieval and manipulation.

What are derived relations in SQL?

• Derived relations are physical tables stored on disk.

• Derived relations are tables that cannot be queried.

• Derived relations are virtual tables created from queries on existing tables.

• Derived relations are only used for data backup purposes.

How can views be created and used in SQL?

• Views can only be created using the SELECT statement.

• Views can be created using the CREATE VIEW statement and used like regular tables in SQL queries.

• Views cannot be used in JOIN operations.

• Views are permanent and cannot be modified once created.

What is the difference between INNER JOIN and OUTER JOIN?

• INNER JOIN and OUTER JOIN are the same and return all rows.

• INNER JOIN includes NULLs for non-matches; OUTER JOIN does not.

• INNER JOIN returns all rows; OUTER JOIN returns only matched rows.

• INNER JOIN returns matched rows; OUTER JOIN returns all rows with NULLs for non-matches.

How do you handle duplicate records in SQL queries?

• Use JOIN to combine records without filtering duplicates.

• Use ORDER BY to sort records and remove duplicates.

• Use DISTINCT or GROUP BY to eliminate duplicates in SQL queries.

• Ignore duplicates and select all records as is.

What is the significance of the GROUP BY clause in SQL?

• The GROUP BY clause is used to filter records based on specific conditions.

• The GROUP BY clause is essential for creating indexes in a database.

• The GROUP BY clause is significant for aggregating data and organizing results into meaningful groups.

• The GROUP BY clause is primarily used for sorting data in ascending order.