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?

<p>SELECT ItemName, Price FROM Products WHERE ItemDescription LIKE '%chocolate%'; (C)</p> Signup and view all the answers

What is the purpose of creating a composite key?

<p>To improve data consistency across multiple tables (B)</p> Signup and view all the answers

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

<p>NOT NULL (D)</p> Signup and view all the answers

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

<p>To uniquely identify a single record in a table (D)</p> Signup and view all the answers

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

<p>To establish a relationship between multiple tables (B)</p> 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'?

<p>SELECT * FROM Orders WHERE NOT ship_state = 'TX' OR NOT ship_state = 'AZ' (D)</p> Signup and view all the answers

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

<p>ALTER TABLE Customers DROP COLUMN SSN; (B)</p> 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?

<p>SELECT, FROM, WHERE, GROUP BY, HAVING (B)</p> Signup and view all the answers

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

<p>DROP VIEW EmployeeView (B)</p> 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?

<p>A foreign key (A)</p> Signup and view all the answers

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

<p>ALTER TABLE (C)</p> Signup and view all the answers

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

<p>To establish a relationship between two tables (C)</p> Signup and view all the answers

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

<p>ALTER TABLE Customers ADD COLUMN SSN; (D)</p> Signup and view all the answers

What is a primary key constraint in a relational database?

<p>A constraint that ensures each row in a table is unique (A)</p> Signup and view all the answers

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

<p>CREATE TABLE Order (OrderID INTEGER, OrderItemID INTEGER, PRIMARY KEY (OrderID, OrderItemID)) (C)</p> Signup and view all the answers

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

<p>Decimal (A)</p> Signup and view all the answers

What is the purpose of the UPDATE statement in SQL?

<p>To update existing records in a table (A)</p> Signup and view all the answers

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

<p>Using the WHERE clause (D)</p> Signup and view all the answers

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

<p>To ensure data integrity by preventing duplicate values (A)</p> Signup and view all the answers

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

<p>SELECT COUNT(*) (B)</p> Signup and view all the answers

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

<p>To ensure each value in a column is unique (B)</p> Signup and view all the answers

Flashcards

Purpose of query A

Retrieving a specific employee's name from a database.

Purpose of query C

Adding a new employee record to a database table.

Purpose of query D

Adding a new column to a table.

Query for chocolate items

Retrieving items containing "chocolate" in their description.

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Composite key

Two or more columns used to uniquely identify a row; maintains data consistency.

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NOT NULL constraint

Ensures a column cannot have a null value.

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Primary key purpose

Uniquely identifying records in a table.

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Foreign key purpose

Creates a relationship between tables by referencing a primary key in another table.

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SQL query for non-TX/AZ orders

Selecting orders not shipped to Texas or Arizona.

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Remove column syntax

Removing a column from a table using ALTER TABLE statement.

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SQL query clause order for unique values

SELECT, FROM, WHERE, GROUP BY, HAVING.

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Drop view statement

Removing a view from a database.

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Constraint for employee-department relation

A foreign key linking employees to departments.

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Remove foreign key SQL

Removing a foreign key constraint from a table.

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Foreign key in relational DB

Establishes relationship between two tables.

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Add column syntax

Adding a column to a table using ALTER TABLE.

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Primary key constraint

Ensuring each row in a table is unique.

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Composite primary key syntax

Creating a primary key using multiple columns.

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Financial data type in SQL

Decimal data type for precise financial values.

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UPDATE statement purpose

Updating existing records in a table.

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UPDATE WHERE clause

Specifying conditions to update rows in SQL.

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PRIMARY KEY constraint purpose

Ensuring data integrity and uniqueness.

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COUNT(*) statement

Counting the number of rows matching the criteria in a table.

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UNIQUE constraint purpose

Ensuring values in a column are unique.

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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.

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