Q41. What is the IN operator?
Answer:IN allows you to specify multiple values in a WHERE clause.
Example: SELECT * FROM Employees WHERE Department IN ('HR', 'Finance');
Q42. What is the EXISTS operator?
Answer:EXISTS checks if a subquery returns any records.
Example: SELECT Name FROM Employees
WHERE EXISTS (SELECT 1 FROM Departments WHERE Employees.DepartmentID = Departments.DepartmentID);
Q43. What is a CASE statement in SQL?
Answer:CASE is used for conditional logic inside SQL queries.
Example: SELECT Name,
CASE
WHEN Age < 18 THEN 'Minor'
ELSE 'Adult'
END AS Status
FROM Employees;
Q44. What is COALESCE function?
Answer:COALESCE returns the first non-NULL value among its arguments.
Example: SELECT Name, COALESCE(Address, 'Address Not Available') FROM Customers;
Q45. What is the ISNULL() function?
Answer:ISNULL() replaces NULL with a specified replacement value.
Example: SELECT ISNULL(Address, 'N/A') FROM Customers;
Q46. What is the DISTINCT keyword?
Answer:DISTINCT is used to return only unique (different) values.
Example: SELECT DISTINCT Department FROM Employees;
Q47. What is the LIKE operator in SQL?
Answer:
(Already given earlier, here again with simple version)
SELECT * FROM Customers WHERE CustomerName LIKE 'A%';
Finds all customer names starting with ‘A’.
Q48. What is an Aggregate Function?
Answer:
Aggregate functions perform a calculation on a set of values and return a single value.
| Function | Use |
|---|---|
| COUNT() | Counts number of rows |
| SUM() | Calculates total sum |
| AVG() | Calculates average |
| MAX() | Finds maximum value |
| MIN() | Finds minimum value |
Q49. What is a Scalar Function?
Answer:
Scalar functions operate on a single value and return a single value.
| Example Function | Purpose |
|---|---|
| UPPER() | Converts to uppercase |
| LOWER() | Converts to lowercase |
| LEN() | Returns string length |
Q50. What is the difference between CHAR and VARCHAR?
Answer:
| CHAR | VARCHAR |
|---|---|
| Fixed length | Variable length |
| Always reserves space | Uses only required space |
| Faster access | Saves memory |
Example:
CHAR(10): Reserves 10 bytes even if 5 characters entered.
VARCHAR(10): Uses only 5 bytes if 5 characters entered.
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