Advanced Logical Expressions
Combining logical functions with operators such as AND, OR, and NOT lets you create more complex conditions in your SQL queries. These logical operators allow you to evaluate multiple expressions at once and control how your queries filter or categorize data. For example, you might want to check if a transaction is both "completed" AND paid by "credit_card", or if a transaction is "pending" OR "failed". The NOT operator can be used to exclude certain results, such as transactions that are NOT "completed". Using these operators inside logical functions provides a powerful way to implement business rules and data categorizations directly within your queries.
1234567891011SELECT transaction_id, amount, status, payment_method, CASE WHEN status = 'completed' AND payment_method = 'credit_card' THEN 'Credit Card Success' WHEN status = 'pending' OR status = 'failed' THEN 'Attention Needed' ELSE 'Other' END AS transaction_status FROM transactions;
You can also use nested CASE statements to handle situations where conditions depend on previous results or require more detailed branching. A nested CASE means placing one CASE expression inside another, allowing you to check additional criteria only when certain conditions are met. This is useful when you want to assign categories or values based on a combination of factors, and your logic needs more than a single layer of decision-making.
1234567SELECT transaction_id, amount, status, payment_method, COALESCE(payment_method, status, 'unknown') AS payment_info FROM transactions;
1. Which operator is used to combine multiple conditions?
2. What is the result of a nested CASE statement?
3. Fill in the blanks to use COALESCE with three arguments.
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Combining logical functions with operators such as AND, OR, and NOT lets you create more complex conditions in your SQL queries. These logical operators allow you to evaluate multiple expressions at once and control how your queries filter or categorize data. For example, you might want to check if a transaction is both "completed" AND paid by "credit_card", or if a transaction is "pending" OR "failed". The NOT operator can be used to exclude certain results, such as transactions that are NOT "completed". Using these operators inside logical functions provides a powerful way to implement business rules and data categorizations directly within your queries.
1234567891011SELECT transaction_id, amount, status, payment_method, CASE WHEN status = 'completed' AND payment_method = 'credit_card' THEN 'Credit Card Success' WHEN status = 'pending' OR status = 'failed' THEN 'Attention Needed' ELSE 'Other' END AS transaction_status FROM transactions;
You can also use nested CASE statements to handle situations where conditions depend on previous results or require more detailed branching. A nested CASE means placing one CASE expression inside another, allowing you to check additional criteria only when certain conditions are met. This is useful when you want to assign categories or values based on a combination of factors, and your logic needs more than a single layer of decision-making.
1234567SELECT transaction_id, amount, status, payment_method, COALESCE(payment_method, status, 'unknown') AS payment_info FROM transactions;
1. Which operator is used to combine multiple conditions?
2. What is the result of a nested CASE statement?
3. Fill in the blanks to use COALESCE with three arguments.
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