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Questions and Answers
What is the purpose of the TRUNCATE statement in DDL?
What is the purpose of the TRUNCATE statement in DDL?
When using the ALTER TABLE statement, what does the DROP command do?
When using the ALTER TABLE statement, what does the DROP command do?
What happens when a database or table is dropped using the DROP statement?
What happens when a database or table is dropped using the DROP statement?
In the context of defining a column in a table, what does 'varchar(20)' signify?
In the context of defining a column in a table, what does 'varchar(20)' signify?
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Which statement correctly describes the ADD command in the ALTER TABLE statement?
Which statement correctly describes the ADD command in the ALTER TABLE statement?
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What is the definition of a tuple in a relational model?
What is the definition of a tuple in a relational model?
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Which of the following statements accurately describes attributes in a database?
Which of the following statements accurately describes attributes in a database?
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Which Codd's rule states that a database must manage information entirely through relational capabilities?
Which Codd's rule states that a database must manage information entirely through relational capabilities?
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According to Codd's rules, which is NOT a correct handling of NULL values?
According to Codd's rules, which is NOT a correct handling of NULL values?
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What does Rule 1, the Information Rule in Codd’s guidelines, emphasize?
What does Rule 1, the Information Rule in Codd’s guidelines, emphasize?
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Which rule necessitates that views theoretically available for updating must be mutable by the system?
Which rule necessitates that views theoretically available for updating must be mutable by the system?
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Which Codd's rule requires that every unique piece of data must be accessible through a combination of Table Name, Primary Key, and Attribute?
Which Codd's rule requires that every unique piece of data must be accessible through a combination of Table Name, Primary Key, and Attribute?
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What role does Rule 5 of Codd’s guidelines pertain to in a relational database?
What role does Rule 5 of Codd’s guidelines pertain to in a relational database?
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What is the purpose of the ROLLBACK command in a database?
What is the purpose of the ROLLBACK command in a database?
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What is the correct order of operations when using a WHERE clause with GROUP BY?
What is the correct order of operations when using a WHERE clause with GROUP BY?
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How does the SAVEPOINT command function in a transaction?
How does the SAVEPOINT command function in a transaction?
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Which of the following statements about the ORDER BY clause is accurate?
Which of the following statements about the ORDER BY clause is accurate?
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If you execute the command 'ROLLBACK TO A' after saving states at points A, B, and C, what will happen?
If you execute the command 'ROLLBACK TO A' after saving states at points A, B, and C, what will happen?
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In which clause can a subquery be utilized?
In which clause can a subquery be utilized?
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In the given example, what does the command 'COMMIT;' do?
In the given example, what does the command 'COMMIT;' do?
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What does a subquery return in SQL?
What does a subquery return in SQL?
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What is the effect of using the ROLLBACK command without a SAVEPOINT specified?
What is the effect of using the ROLLBACK command without a SAVEPOINT specified?
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Why are nested queries considered powerful in SQL?
Why are nested queries considered powerful in SQL?
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Which of the following describes the role of DCL commands?
Which of the following describes the role of DCL commands?
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What will the state of the class table look like after executing 'ROLLBACK TO B'?
What will the state of the class table look like after executing 'ROLLBACK TO B'?
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What should always enclose a subquery?
What should always enclose a subquery?
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Which SQL command would be used to create a temporary marker in a database transaction?
Which SQL command would be used to create a temporary marker in a database transaction?
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When is the ORDER BY clause applied in the query execution process?
When is the ORDER BY clause applied in the query execution process?
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What happens if the GROUP BY clause is omitted in a SQL statement with an aggregate function?
What happens if the GROUP BY clause is omitted in a SQL statement with an aggregate function?
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What does the IN operator do in the context of a nested query?
What does the IN operator do in the context of a nested query?
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Which of the following queries correctly retrieves students with GPAs above the average?
Which of the following queries correctly retrieves students with GPAs above the average?
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What is the purpose of the ANY operator in a nested query?
What is the purpose of the ANY operator in a nested query?
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How would you use the NOT IN operator effectively in a query?
How would you use the NOT IN operator effectively in a query?
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What will the following SQL query return? SELECT * FROM students WHERE GPA > 3.19;
What will the following SQL query return? SELECT * FROM students WHERE GPA > 3.19;
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Which of the following describes the function of the subquery in SELECT * FROM students WHERE GPA > (SELECT AVG(GPA) FROM students);?
Which of the following describes the function of the subquery in SELECT * FROM students WHERE GPA > (SELECT AVG(GPA) FROM students);?
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What data type is returned by the subquery SELECT AVG(GPA) FROM students?
What data type is returned by the subquery SELECT AVG(GPA) FROM students?
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Why is it important for the subquery in the context of GPA to return a single value?
Why is it important for the subquery in the context of GPA to return a single value?
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Study Notes
Database Concepts
- Tuple: Represents a single row in a table containing one record for that relation.
-
Attributes: Table headers that define permissible values known as the domain (e.g., the attribute
branch_nameincludes all valid branch names). - Relation: Refers to a table in the relational model of data storage.
- RDBMS (Relational Database Management System): A database system based on the relational model for storing and accessing data.
Codd's Rules for RDBMS
- E.F. Codd: Computer scientist who developed the relational model and proposed 12 rules to define the quality of a DBMS.
- Rule 0: A system qualifies as an RDBMS if it manages data solely through relational capabilities.
- Rule 1 (Information Rule): All information, including metadata, must be stored in tables, and rows and columns should remain unordered.
- Rule 2 (Guaranteed Access): Atomic data should be accessible through a combination of table name, primary key, and attribute.
- Rule 3 (Systematic Treatment of NULL): NULL should be consistently managed and must never occur in a primary key.
- Rule 4 (Active Online Catalog): The database catalog must be stored online and governed by the same rules as the database itself.
- Rule 5 (Powerful Language): A structured query language must provide access to database data, e.g., SQL.
- Rule 6 (View Updation): Updatable views must be supported by the system.
- Rule 7 (Relational Level Operations): Insert and Update operations must exist at each relation level.
SQL Commands
-
CREATE TABLE: Defines a new table with specified attributes. E.g.,
Students(ROLL_NO int(3), NAME varchar(20), SUBJECT varchar(20)); -
DROP: Deletes an entire table or database. Syntax:
DROP TABLE table_name; -
TRUNCATE: Removes all data from a table while preserving its structure for future use. Syntax:
TRUNCATE TABLE table_name; -
ALTER: Modifies an existing table to add, drop, or modify columns and constraints.
-
ADD: Adds new columns. Syntax:
ALTER TABLE table_name ADD (column_name datatype, ...); -
DROP: Deletes unwanted columns. Syntax:
ALTER TABLE table_name DROP COLUMN column_name; - MODIFY: Changes existing column attributes.
-
ADD: Adds new columns. Syntax:
Transaction Management
-
ROLLBACK: Restores a database to the last committed state. Useful to revert unwanted changes. Syntax:
ROLLBACK TO savepoint_name; -
SAVEPOINT: Temporarily saves a transaction state, allowing rollback to that point. Syntax:
SAVEPOINT savepoint_name;
Data Control Language (DCL)
- DCL: Manages user privileges for database operations.
- When used with
GROUP BY, theWHEREclause filters rows before groups are formed.
Query Features
-
ORDER BY Clause: Sorts query results in ascending or descending order, using specified columns for sorting. Syntax:
SELECT ... FROM table_name [WHERE condition] ORDER BY col1, col2, ...; -
Nested Queries: A query within a query, where the inner query's result informs the outer query.
- Allows tasks to be performed more efficiently by consolidating operations.
- Subqueries can filter data in various clauses (WHERE, FROM, SELECT, HAVING) and should always be enclosed in parentheses.
Example of Nested Query
- To find students with GPAs above the average:
- Use a subquery to calculate average GPA:
SELECT AVG(GPA) FROM students; - Combine with an outer query:
SELECT * FROM students WHERE GPA > (SELECT AVG(GPA) FROM students);
- Use a subquery to calculate average GPA:
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Description
This quiz covers fundamental concepts in databases, specifically focusing on tuples, attributes, and relations. Understand how single rows in a table represent records and the significance of attributes as headers. Dive into the relational data model and its structure to better grasp database organization.
