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Questions and Answers
What does the AND operator do in a WHERE clause?
What is the purpose of the NOT operator in SQL?
Which of the following statements accurately describes a PRIMARY KEY?
What does the INSERT INTO SELECT statement do?
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How does the CASE expression function in SQL?
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What is the role of a FOREIGN KEY in a database?
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When copying data from one table to another, what must be ensured regarding the data types?
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What happens if no conditions in a CASE expression are true?
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Study Notes
SQL Overview
- SQL stands for Structured Query Language, used for managing and manipulating relational databases.
WHERE Clause and Operators
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The WHERE clause filters records based on conditions.
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The AND operator requires all specified conditions to be true.
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Example:
- Selecting fields from Customers where Country is "Germany," City is "Berlin," and PostalCode is greater than 12000.
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The OR operator allows filtering based on multiple conditions, with any condition being true.
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The NOT operator inverts conditions, providing the opposite result.
SQL INSERT INTO SELECT
- Allows copying data from one table into another.
- The data types in source and target tables must match.
- Syntax varies based on whether all or specific columns are copied.
- Example for copying:
- All columns from "Suppliers" into "Customers" may leave non-filled columns as NULL.
- Filling all columns requires additional handling in the syntax.
- Copying only German suppliers into "Customers" targets specific data.
SQL CASE Expression
- The CASE expression evaluates conditions and returns the first true condition's value.
- Functions similarly to an if-then-else structure.
- Stops evaluating once a true condition is encountered; returns the ELSE value if no conditions are met.
SQL PRIMARY KEY
- A PRIMARY KEY constraint uniquely identifies records in a table.
- Must contain unique values and cannot contain NULL values.
SQL FOREIGN KEY
- A FOREIGN KEY constraint maintains relationships between tables.
- Refers to a PRIMARY KEY in another table, helping to prevent actions that could break these connections.
- The table containing the foreign key is known as the child table, while the table with the primary key is the parent table.
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Description
This quiz covers the use of the WHERE clause in SQL, focusing on the AND and OR operators. You'll learn how to construct queries that select records based on multiple conditions. Test your understanding of SQL syntax and statement construction.
