Q101. Which statement deletes data?
The **`DELETE`** statement removes existing rows from a table based on a condition: ```sql DELETE FROM Customers WHERE is_active = 0 AND last_login < '2023-01-01'; ``` ##...
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Q102. Delete records where FirstName is "John"?
To delete all rows where `FirstName` equals "John": ```sql DELETE FROM Customers WHERE FirstName = 'John'; ``` *Safety Warning:* If you accidentally omit `WHERE FirstName...
Q103. What is FROM used for?
The **`FROM`** clause defines the source table(s), views, joined datasets, or subqueries from which rows are read: ```sql SELECT u.username, p.title FROM users u INNER JO...
Q104. DELETE vs TRUNCATE?
See the comparison table above. Key differences: `DELETE` is DML (row-by-row, rollbackable, fires triggers, has WHERE). `TRUNCATE` is DDL (bulk page deallocation, faster,...
Q105. Which statement creates a table?
The **`CREATE TABLE`** statement defines and provisions a new table schema: ```sql CREATE TABLE Customers ( customer_id INT AUTO_INCREMENT PRIMARY KEY, first_name VARCHAR...
Q106. What is database collation and how does it affect SQL queries?
Collation defines the **rules for comparing and sorting** characters. It works with the character set. - `utf8mb4_general_ci`: Case-insensitive, faster - `utf8mb4_unicode...
Q107. What is AUTO_INCREMENT?
Automatically generates sequential unique integers for a column, typically the PRIMARY KEY. ```sql CREATE TABLE users (id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(50)...
Q108. Valid constraints in MySQL?
MySQL supports a complete set of integrity constraints: 1. **`PRIMARY KEY`**: Uniquely identifies each row (implies `NOT NULL` and `UNIQUE`). 2. **`FOREIGN KEY`**: Enforc...
Q109. Which is NOT TRUE about constraints?
Any assertion claiming that **constraints are optional in production** or that **constraints significantly slow down reads** is false. ### Why Constraints Are Vital: - Co...
Q110. NOT NULL constraint?
The **`NOT NULL`** constraint enforces that a column must always contain a valid data value and cannot accept `NULL`: ```sql CREATE TABLE employees ( id INT PRIMARY KEY, ...