Computer Science
Grade 7
20 min
Basic Queries
Basic Queries
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1
Introduction & Learning Objectives
Learning Objectives
Define the terms database, table, and query.
Identify the purpose of the SELECT, FROM, and WHERE clauses in a basic query.
Write a simple query to retrieve all data from a single table using the '*' wildcard.
Write a query to retrieve specific, named columns from a table.
Write a query that filters data using a WHERE clause with a single condition.
Use comparison operators like '=', '>', and '<' to filter numerical data.
How does your favorite music app instantly find a song out of millions? How does a game save your character's level and items? 🎮 They use special questions called queries!
In this lesson, you'll become a data detective! You will learn how to ask questions to a database using a spec...
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Key Concepts & Vocabulary
TermDefinitionExample
DatabaseAn organized collection of information, like a giant digital filing cabinet for storing data.A school's database might have information about students, teachers, classes, and grades.
TableA set of data arranged in columns and rows within a database. Each table stores information about one specific type of thing.A 'Students' table would have columns for StudentID, FirstName, and Grade.
ColumnA vertical category of data in a table that contains a specific type of information for every row.In a 'Students' table, 'FirstName' would be a column.
RowA single, horizontal record of data in a table. It represents one complete item.A single row in the 'Students' table might be: 101, 'Ada', 'Lovelace', 7.
Q...
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Core Syntax & Patterns
Select All Pattern
SELECT * FROM TableName;
Use this to get ALL columns and ALL rows from a table. The asterisk (*) is a wildcard that means 'all columns'.
Select Specific Columns Pattern
SELECT ColumnName1, ColumnName2 FROM TableName;
Use this to get only the specific columns you list from a table. This is useful when you don't need to see every piece of information.
Filtering Pattern
SELECT ColumnName(s) FROM TableName WHERE Condition;
Use this to get only the rows that match a specific condition. The WHERE clause acts like a filter, similar to an 'if' statement in programming.
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Challenging
Student A runs `SELECT CharacterName FROM GameCharacters WHERE Level > 5;`. Student B runs `SELECT * FROM GameCharacters WHERE Level > 5;`. Both queries filter for the same characters. What is the key difference in the output they will see?
A.Student A will see more rows than Student B.
B.Student B will see more rows than Student A.
C.Student A will only see the names of the characters, while Student B will see all information about them.
D.There is no difference in the output.
Challenging
You run the query `SELECT CustomerName FROM Orders WHERE OrderTotal > 100;` to find big spenders. The result is empty, but you are certain there are orders over $100. Based on the common pitfalls, what is the MOST likely error?
A.The table name `Orders` or column name `OrderTotal` is misspelled.
B.You cannot use `>` with numbers over 100.
C.The semicolon at the end is missing.
D.You should have used `SELECT *` instead.
Challenging
A game designer wants to find the name and type of all characters who are exactly level 20. The table is `GameCharacters` and the columns are `CharacterName`, `Level`, and `CharacterType`. Construct the complete and correct query.
A.SELECT * FROM GameCharacters WHERE Level = 20;
B.SELECT CharacterName, CharacterType FROM GameCharacters WHERE Level > 20;
C.SELECT CharacterName, CharacterType FROM GameCharacters WHERE Level = 20;
D.SELECT CharacterName, Level FROM GameCharacters WHERE CharacterType = 20;
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