Result Set Construction and Delivery
When a SQL query is executed, the database engine processes the execution plan and begins constructing the result set. Each row retrieved by the plan is formatted according to the query's output requirements. The engine may buffer rows in memory, especially if the result is large, to manage memory and network resources efficiently. Once rows are ready, the engine starts delivering them to the client application, often in batches or chunks, so the client can begin processing results without waiting for the entire set to be built. This approach reduces latency and improves responsiveness, especially for large queries.
1234SELECT employee_id, first_name, last_name FROM employees ORDER BY hire_date DESC LIMIT 3 OFFSET 2;
The LIMIT and OFFSET clauses control how many rows are included in the final result set and where to start delivering them. LIMIT restricts the maximum number of rows returned, while OFFSET skips a specified number of initial rows. This means the SQL engine only needs to fetch and format the relevant subset, which speeds up delivery for large tables or paginated results. As soon as the required rows are ready, they are sent to the client, making the process more efficient and responsive.
123SELECT employee_id AS "ID", first_name AS "First Name", salary AS "Annual Salary" FROM employees WHERE department_id = 2;
1. What is the effect of the LIMIT clause in a SQL query?
2. How does the SQL engine deliver results to the client application?
3. Fill in the blank: The result set is constructed ________ the execution plan has processed all relevant rows.
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When a SQL query is executed, the database engine processes the execution plan and begins constructing the result set. Each row retrieved by the plan is formatted according to the query's output requirements. The engine may buffer rows in memory, especially if the result is large, to manage memory and network resources efficiently. Once rows are ready, the engine starts delivering them to the client application, often in batches or chunks, so the client can begin processing results without waiting for the entire set to be built. This approach reduces latency and improves responsiveness, especially for large queries.
1234SELECT employee_id, first_name, last_name FROM employees ORDER BY hire_date DESC LIMIT 3 OFFSET 2;
The LIMIT and OFFSET clauses control how many rows are included in the final result set and where to start delivering them. LIMIT restricts the maximum number of rows returned, while OFFSET skips a specified number of initial rows. This means the SQL engine only needs to fetch and format the relevant subset, which speeds up delivery for large tables or paginated results. As soon as the required rows are ready, they are sent to the client, making the process more efficient and responsive.
123SELECT employee_id AS "ID", first_name AS "First Name", salary AS "Annual Salary" FROM employees WHERE department_id = 2;
1. What is the effect of the LIMIT clause in a SQL query?
2. How does the SQL engine deliver results to the client application?
3. Fill in the blank: The result set is constructed ________ the execution plan has processed all relevant rows.
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