Q21. Select all records where FirstName is "John"?
To retrieve all columns for records where `FirstName` equals 'John', combine `SELECT *` with a `WHERE` equality filter: ```sql SELECT * FROM Customers WHERE FirstName = '...
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Q22. OR vs AND?
`AND` requires ALL conditions to be true. `OR` requires ANY to be true. Use parentheses to control precedence — `AND` binds tighter than `OR`. ```sql -- Without parenthes...
Q23. Which comparison operators exist?
Relational SQL engines provide a rich set of comparison operators evaluated in `WHERE` and `HAVING` clauses: | Operator | Meaning | Example | | :--- | :--- | :--- | | `=`...
Q24. Select records where FirstName="John" AND LastName="Jackson"?
To retrieve records that satisfy multiple simultaneous criteria, use the **`AND`** logical conjunction operator: ```sql SELECT * FROM Customers WHERE FirstName = 'John' A...
Q25. How to select 10 random rows?
```sql -- MySQL SELECT * FROM tbl ORDER BY RAND() LIMIT 10; -- PostgreSQL SELECT * FROM tbl ORDER BY RANDOM() LIMIT 10; -- SQL Server SELECT TOP 10 * FROM tbl ORDER BY NE...
Q26. What does ISNULL(price, 50) return if price is NULL?
If `price` is `NULL`, `ISNULL(price, 50)` evaluates to **`50`**. ### Function Nuances Across Databases: 1. **SQL Server**: `ISNULL(check_expression, replacement_value)` r...
Q27. Which operator searches text patterns?
`LIKE` with wildcards `%` (zero or more chars) and `_` (single char). ```sql WHERE name LIKE 'A%' -- starts with A WHERE name LIKE '%a%' -- contains a WHERE name LIKE '_a...
Q28. Details of students whose FirstName starts with 'K'?
To find records where a text column begins with a specific letter or prefix, use the **`LIKE`** operator with the `%` wildcard: ```sql SELECT * FROM Students WHERE FirstN...
Q29. Which operator selects values in a range?
The **`BETWEEN`** operator selects values within an inclusive range (numbers, text strings, or dates): ```sql SELECT product_id, name, price FROM products WHERE price BET...
Q30. Correct syntax for date range?
```sql SELECT * FROM Sales WHERE Date BETWEEN '2017-12-01' AND '2018-01-01'; ``` Use ISO-8601 format (`YYYY-MM-DD`) to avoid locale issues.