SQL Clauses and Keywords Quiz

Retrieving Data from a Table

• To retrieve all columns from a table, use the SELECT * statement, where * is a wildcard character representing all columns.
• Example: SELECT * FROM Books retrieves all columns from the "Books" table.

Creating a New Table with a Subquery

• A subquery can be used to create a new table with the CREATE TABLE statement.
• Example: CREATE TABLE BestSellers AS (SELECT * FROM Books WHERE PublishedYear = 2022 AND Price > 20) creates a new table "BestSellers" with the same structure as the result of the subquery.

Identifying Table Structure

• The DESCRIBE statement can be used to identify the table structure (columns and their data types) in some database systems, such as MySQL or PostgreSQL.
• Marking a column as unused can be achieved by renaming the column or creating a new table without the unwanted column.
• Deleting an unused column permanently removes the column from the table.

Data Manipulation Language (DML) Commands

• DML commands are used for manipulating and interacting with the data stored in a database.
• Key DML commands include:
  • SELECT: retrieves data from one or more tables.
  • INSERT: adds new records to a table.
  • UPDATE: modifies existing records in a table.
  • DELETE: removes records from a table.

SQL Clauses

• GROUP BY clause: groups rows based on specified columns, often used with aggregate functions.
• HAVING clause: filters groups based on aggregate conditions.
• ORDER BY clause: sorts the result set based on specified columns and sorting orders.
• LIMIT (or FETCH) clause: restricts the number of rows returned in the result set.
• JOIN clause: combines rows from two or more tables based on related columns.
• DISTINCT keyword: ensures that only unique values are returned.

Test your knowledge on SQL clauses like GROUP BY, HAVING, ORDER BY, LIMIT, JOIN, and keywords like DISTINCT. Learn how to group rows, filter groups, sort results, restrict row count, combine tables, and retrieve unique values in SQL queries.