SQL Queries for Filtering States

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Questions and Answers

What is the purpose of the query in option A?

To retrieve a specific employee's name (correct)

To delete an employee from the database

To insert a new employee into the database

To update an existing employee's information

What is the purpose of the query in option C?

To delete an employee from the database

To insert a new employee into the database (correct)

To retrieve an employee's name

To update an existing employee's information

What is the purpose of the query in option D?

To add a new column to the Employee table (correct)

To modify an existing column in the Employee table

To rename a column in the Employee table

To remove a column from the Employee table

Which query will retrieve ItemName and Price when 'chocolate' appears in the ItemDescription column?

SELECT ItemName, Price FROM Products WHERE ItemDescription LIKE '%chocolate%'; Signup and view all the answers

What is the purpose of creating a composite key?

To improve data consistency across multiple tables Signup and view all the answers

What type of database constraint ensures that a column does not contain null values?

NOT NULL Signup and view all the answers

What is the purpose of a primary key in a database table?

To uniquely identify a single record in a table Signup and view all the answers

What is the purpose of a foreign key in a database table?

To establish a relationship between multiple tables Signup and view all the answers

What is the correct SQL query to select all orders from the Orders table where the ship state is not 'TX' or 'AZ'?

SELECT * FROM Orders WHERE NOT ship_state = 'TX' OR NOT ship_state = 'AZ' Signup and view all the answers

What is the correct syntax to remove a column from a table in SQL?

ALTER TABLE Customers DROP COLUMN SSN; Signup and view all the answers

What is the correct order of clauses in a SQL query to determine whether a value appears only once in a table?

SELECT, FROM, WHERE, GROUP BY, HAVING Signup and view all the answers

What is the correct statement to remove a view from a database?

DROP VIEW EmployeeView Signup and view all the answers

What should you apply to the Employee table to ensure that an employee can be assigned to only an existing department?

A foreign key Signup and view all the answers

What is the correct statement to remove a foreign key from a table?

ALTER TABLE Signup and view all the answers

What is the purpose of a foreign key in a relational database?

To establish a relationship between two tables Signup and view all the answers

What is the correct syntax to alter a table to add a new column in SQL?

ALTER TABLE Customers ADD COLUMN SSN; Signup and view all the answers

What is a primary key constraint in a relational database?

A constraint that ensures each row in a table is unique Signup and view all the answers

What is the correct syntax to create a composite primary key in SQL?

CREATE TABLE Order (OrderID INTEGER, OrderItemID INTEGER, PRIMARY KEY (OrderID, OrderItemID)) Signup and view all the answers

Which data type is suitable for storing financial data in a database table?

Decimal Signup and view all the answers

What is the purpose of the UPDATE statement in SQL?

To update existing records in a table Signup and view all the answers

How do you specify a condition in an UPDATE statement to update only specific records?

Using the WHERE clause Signup and view all the answers

What is the purpose of the PRIMARY KEY constraint in a relational database?

To ensure data integrity by preventing duplicate values Signup and view all the answers

Which SQL statement is used to count the number of rows in a table?

SELECT COUNT(*) Signup and view all the answers

What is the purpose of the UNIQUE constraint in a relational database?

To ensure each value in a column is unique Signup and view all the answers

Study Notes

SQL Queries

SELECT statement can be used to retrieve data from a table, with NOT operator to exclude certain values, e.g., SELECT * FROM Orders WHERE NOT ship_state = 'TX' AND NOT ship_state = 'AZ'.
Using OR instead of AND in the query can alter the result, including more records, e.g., SELECT * FROM Orders WHERE NOT ship_state = 'TX' OR NOT ship_state = 'AZ'.

Database Modifications

To remove a column from a table, use ALTER TABLE Customers DROP COLUMN SSN;.
To drop a view, use DROP VIEW EmployeeView;.
To remove a foreign key, use ALTER TABLE ... DROP FOREIGN KEY ...;.

Query Errors

A query with a syntax error may be due to incorrect ordering of clauses, e.g., SELECT Title FROM Movie WHERE Title = 'Sample Movie' ORDER BY Title GROUP BY Title HAVING COUNT(*) = 1.
Correcting the query by removing the ORDER BY clause can resolve the error.

Table Structure

Each row in a table must be unique.
Each column name in a table must be unique.
A value in a field in a table does not have to be unique.

Data Types

For financial calculations, a decimal data type is recommended, e.g., for storing charge amounts.

Updating Tables

To update a table, use UPDATE LoanedBooks SET Books = 0 WHERE (NAME = 'Harry' AND City = 'San Francisco');.
Use specific conditions to update the correct record.

Retrieving Data

To return the number of rows in a table, use SELECT COUNT(*) FROM Employee;.
To retrieve specific data, use SELECT ItemName, Price FROM Products WHERE ItemDescription LIKE '%chocolate%';.

Composite Key

A composite key is created when a primary key consists of multiple columns, e.g., CREATE TABLE Order (OrderID INTEGER, OrderItemID INTEGER, PRIMARY KEY (OrderID, OrderItemID));.

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Description

This quiz tests your understanding of SQL queries, specifically in filtering data based on state information. Identify the correct SQL query to retrieve data excluding certain states.