Q131. Default isolation level in MySQL?
**REPEATABLE READ** (InnoDB engine). Prevents dirty reads and non-repeatable reads, but phantom reads are possible (though InnoDB uses MVCC + gap locking to mostly preven...
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Q132. Is autocommit enabled by default in MySQL?
**Yes**, in MySQL (using the standard InnoDB storage engine), **autocommit is enabled by default** (`autocommit = 1`): ### What Autocommit Means: - Every individual SQL s...
Q133. What is a virtual table in MySQL?
In MySQL and relational databases, a **virtual table** is called a **View**: ```sql CREATE VIEW active_customer_summary AS SELECT id, first_name, last_name, email FROM Cu...
Q134. Are views updatable?
**Some views are updatable, but under strict structural criteria**: ### Conditions for a View to Be Updatable: 1. Must reference **only one base table** in the `FROM` cla...
Q135. Advantages of views?
1. **Simplify complex queries** — hide JOINs and aggregations 2. **Security** — expose only specific columns/rows 3. **Logical independence** — shield apps from schema ch...
Q136. Does a view contain data?
**Standard SQL views do NOT contain data**. - **Standard Views (Virtual)**: Contain only a stored SQL query definition in the data dictionary. Every query against the vie...
Q137. How to remove a view?
To delete a view from the database, use the **`DROP VIEW`** command: ```sql DROP VIEW IF EXISTS active_customer_summary; ``` Dropping a view removes only the stored query...
Q138. Can a view be based on another view?
**Yes**, a view can be defined on top of another existing view (known as a **nested view**): ```sql CREATE VIEW us_customers AS SELECT * FROM Customers WHERE country = 'U...
Q139. Iterate over rows in a stored procedure?
To iterate row-by-row over a query result set inside a stored procedure, use a **`CURSOR`**: ### Cursor Lifecycle Steps: 1. **`DECLARE`**: Define the cursor and query. 2....
Q140. Process of finding a good query execution strategy?
**Query optimization**. The database's query optimizer generates multiple execution plans and picks the cheapest one based on statistics, indexes, and cost models. You ca...