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Questions and Answers
What does SQL stand for?
Structured Query Language
SQL was originally called SEQUEL.
True
What does DDL stand for?
Data Defining Language
Which of the following is NOT a sub-language of SQL?
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The SQL command to permanently remove a table from a database is called ___
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What is the purpose of the ALTER command in SQL?
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Which of the following SQL commands is used to create a new table?
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What is one reason why SQL is widely used?
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What does the TRUNCATE command do in SQL?
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Study Notes
Introduction to SQL
- SQL (Structured Query Language) is essential for managing relational databases (RDBMS).
- Developed in 1970 at IBM, was standardized by ANSI in 1986 and by ISO in 1987.
- Originally named SEQUEL (Structured English Query Language); standardized name is SQL.
- Widely used across various RDBMS platforms including Oracle, MySQL, MS Access, and SQL Server.
Importance of SQL
- Enables easy data manipulation by allowing users to view, add, delete, and modify database records quickly.
- SQL queries simplify finding specific data through filtering methods and summarizing data effectively.
- SQL is case-insensitive, allowing flexibility in letter casing when writing commands.
SQL Sub-Languages
- SQL comprises five sub-languages: DDL (Data Definition Language), DML (Data Manipulation Language), DQL (Data Query Language), DCL (Data Control Language), and TCL (Transaction Control Language).
Data Definition Language (DDL)
- DDL commands modify the table structure and are automatically committed.
- Key DDL commands include:
-
CREATE: Establishes new tables and indexes. Example:
CREATE table Student (Roll_number INTEGER(5), Name VARCHAR(30), Age INTEGER(3), City VARCHAR(30)); -
ALTER: Changes an existing table's structure (e.g., adding/modifying columns). Example:
ALTER TABLE Student ADD (Ph_number INTEGER(12)); -
RENAME: Changes the name of an existing table using the ALTER command. Example:
ALTER TABLE Student RENAME TO Student_details; -
DROP: Permanently deletes a table. Example:
DROP TABLE Student; -
TRUNCATE: Removes all rows from a table while retaining its structure. Example:
TRUNCATE TABLE Student;
-
CREATE: Establishes new tables and indexes. Example:
SQL Query Example
- An SQL query to select customer data between specific dates is:
SELECT customer_name, order_date, total_amount FROM orders WHERE order_date BETWEEN '2023-01-01' AND '2023-12-31' ORDER BY total_amount DESC; - This query fetches customer names, order dates, and total amounts for orders made in 2023, sorted by total amount in descending order.
Conclusion
- Understanding SQL sub-languages and commands is critical for effective database management, enabling tasks from table creation to data manipulation and structural changes.
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Description
This quiz covers the basics of SQL, focusing on its commands and sub-languages essential for relational database management. Learn about the history of SQL and its importance in managing databases effectively. Test your knowledge on how to create, access, and manipulate databases using SQL.
