Python Lesson 25: MySQL WHERE Clause

Questions and Answers

What statement is used to filter selections in MySQL?

WHERE

What keyword is used for sorting results in MySQL?

ORDER BY

The DELETE FROM statement will only delete specific records if a WHERE clause is included.

True

The DROP TABLE statement can be used without error even if the specified table does not exist.

False Signup and view all the answers

To update records in a MySQL table, you use the ______ statement.

UPDATE Signup and view all the answers

To commit changes to a database in MySQL, you need to call ______.

mydb.commit() Signup and view all the answers

Match the exception types with their descriptions:

AssertionError = Raised when the assert statement fails. TypeError = Raised when an operation is applied to an incorrect type. ImportError = Raised when the imported module is not found. ZeroDivisionError = Raised when the second operand of a division operation is zero. Signup and view all the answers

What keyword is used in Python to handle exceptions?

try Signup and view all the answers

A set in Python is written with ______ brackets.

curly Signup and view all the answers

Which method is used to add a single item to a set in Python?

add() Signup and view all the answers

Python sets can contain mutable objects like lists or dictionaries.

False Signup and view all the answers

The ______ method removes the last item from a set.

pop() Signup and view all the answers

What is the purpose of the raise keyword in Python?

To throw an exception. Signup and view all the answers

Which of these is NOT a type of exception in Python?

LinkError Signup and view all the answers

Study Notes

MySQL Basics

WHERE Clause: Use to filter selections based on specified conditions when querying records.
Wildcard Characters: The % symbol acts as a wildcard to match any string of characters.
SQL Injection Prevention: Escape user-provided query values to secure against SQL injection attacks.
mysql.connector Module: Contains methods to safely escape query values to mitigate SQL injection risks.

Sorting and Deleting Records

ORDER BY Statement: Sorts query results, ascending by default. Use DESC for descending order.
DELETE FROM Statement: Removes records from a table. Always use a WHERE clause to specify which records to delete; omitting it deletes all records.
mydb.commit(): Essential to make changes permanent in the database after a delete operation.

Table Management

DROP TABLE Statement: Deletes an existing table from the database.
IF EXISTS Clause: Prevents errors from attempting to drop a non-existent table.

Updating Records

UPDATE Statement: Modifies existing records in a table. Always include a WHERE clause to prevent updating all records.
correct use of mydb.commit(): Ensures that changes made by the UPDATE statement are saved in the database.

Python Error Handling

Try-Except Block: Use try to test code for errors; except to handle exceptions. A finally block executes code regardless of the try-except result.
Common Exceptions: Includes NameError, AttributeError, KeyError, and ZeroDivisionError, among others.
Using Else: Allows defining a code block that runs if no errors occur in the try block.
Raising Exceptions: Utilize raise to throw exceptions deliberately when certain conditions are met.

Python Sets

Definition: Sets are unordered, unindexed collections denoted by curly brackets.
Accessing Items: Items can't be accessed via indices but can be checked for presence using the in keyword.
Adding and Removing Items: Use add() to include an item; remove() or discard() to delete an item. pop() removes an arbitrary item.
Joining Sets: Use union() to create a new set with combined elements or update() to insert items into an existing set.

Set Characteristics

Uniqueness: Sets automatically discard duplicates.
Membership Testing: Fast checks for element existence compared to lists.
Set Operations: Support union, intersection, and difference operations for comparative analyses of data.
Mutability of Set: Sets are mutable, but their contents must be immutable types, such as strings and tuples.

PyCharm Setup and Project Management

Downloading PyCharm: Available online; check “Update PATH Variable” during installation.
Creating a New Project: Navigate through File > New Project, name it, and click “Create.”
Running Python Scripts: Right-click on the project file to create a new Python file. Use Run > Run to execute scripts.

Description

This quiz covers the MySQL WHERE clause focusing on selecting records with filters. Learn how to use wildcard characters for more dynamic queries and understand the importance of preventing SQL injection vulnerabilities. Test your knowledge on these crucial SQL concepts through practical questions.