Free SQL Basic Practice

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SQL Basic Practice Quiz

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Question 1 of 5

1. Question
Consider the query:
```
SELECT * 
FROM employees
WHERE dept_id NOT IN (10, 20, NULL);
```
What will this query return?
- All employees except those in departments 10 and 20
- Employees whose department is not 10 or 20
- No rows returned
- Only employees whose dept_id is NULL
Correct

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Question 2 of 5

2. Question
What will happen when this query is executed?
```
SELECT salary * 12 AS annual_salary
FROM employees
WHERE annual_salary > 600000;
```
- Returns employees earning more than 600000 annually
- Returns no rows
- Produces an error because alias cannot be used in WHERE
- Works only in MySQL but fails in PostgreSQL
Correct

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Question 3 of 5

3. Question
What is the result of the following query?
```
SELECT COUNT(*)
FROM employees
GROUP BY dept_id
ORDER BY COUNT(*) DESC
LIMIT 1;
```
- Total number of employees
- Department with highest employee count
- The largest employee count among departments
- Syntax error
Correct

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Question 4 of 5

4. Question
Consider the following transaction:
```
START TRANSACTION;
TRUNCATE TABLE employees;
ROLLBACK;
```
What will be the final state of the employees table in most SQL databases?
- Table remains truncated
- Table data is restored after rollback
- Table structure is deleted
- Depends on WHERE clause in TRUNCATE
Correct

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Question 5 of 5

5. Question
Consider the query:
```
SELECT name, salary, dept_id
FROM employees
ORDER BY 2 DESC;
```
What does ORDER BY 2 refer to?
- Second column in the table definition
- Second column in the SELECT list
- Column with index 2 in the database
- Column named "2"
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