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Top 100 SQL Joins Interview Questions and Answers

Top 100 SQL Joins Interview Questions and Answers
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1. What is an SQL Join?

Answer: An SQL Join is used to combine rows from two or more tables based on a related column between them. It helps retrieve meaningful information from multiple tables.


2. What are the types of SQL Joins?

Answer: There are four types of SQL Joins: INNER JOIN, LEFT JOIN (or LEFT OUTER JOIN), RIGHT JOIN (or RIGHT OUTER JOIN), and FULL JOIN (or FULL OUTER JOIN).


3. Explain INNER JOIN with an example.

SELECT *
FROM customers
INNER JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: INNER JOIN retrieves records that have matching values in both tables based on the specified condition (customers.customer_id = orders.customer_id).


4. Explain LEFT JOIN with an example.

SELECT *
FROM customers
LEFT JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: LEFT JOIN returns all records from the left table (customers), and the matched records from the right table (orders). If no match is found, NULL values are returned.


5. Explain RIGHT JOIN with an example.

SELECT *
FROM customers
RIGHT JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: RIGHT JOIN returns all records from the right table (orders), and the matched records from the left table (customers). If no match is found, NULL values are returned.


6. Explain FULL JOIN with an example.

SELECT *
FROM customers
FULL JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: FULL JOIN returns all records when there is a match in one of the tables. It combines the results of both LEFT JOIN and RIGHT JOIN.


7. What is a self-join?

Answer: A self-join is a join that occurs when a table is joined with itself. It is used to combine rows with related data within the same table.


8. Explain CROSS JOIN with an example.

SELECT *
FROM customers
CROSS JOIN products;

Answer: CROSS JOIN produces a Cartesian product of both tables, meaning it combines every row from the first table with every row from the second table.


9. What is a natural join?

Answer: A natural join is a type of join that automatically matches columns with the same name in both tables. It’s considered a best practice to avoid using it due to ambiguity.


10. Explain the USING clause in SQL Joins.

SELECT *
FROM customers
JOIN orders
USING (customer_id);

Answer: The USING clause is used to specify a list of columns to join. It’s a shorthand for specifying the equality condition.


11. How do you handle NULL values in Joins?

Answer: To handle NULL values in Joins, use COALESCE() or IFNULL() functions to replace NULLs with appropriate values, ensuring meaningful results.


12. Explain the difference between INNER JOIN and OUTER JOIN.

Answer: INNER JOIN returns only matching rows, excluding non-matching ones. OUTER JOIN returns all rows from at least one table, filling in NULLs for non-matching rows.


13. What is the performance impact of different types of Joins?

Answer: INNER JOINs are generally faster than OUTER JOINs because they involve fewer records. LEFT JOINs and RIGHT JOINs have similar performance.


14. When would you use a CROSS JOIN?

Answer: CROSS JOIN is used when there’s a need to combine every row from one table with every row from another, such as in generating permutations.


15. What is the result of a Join when no matching rows are found?

Answer: For INNER JOIN, no result is returned. For LEFT JOIN, the left table’s rows are returned with NULL values for columns from the right table. For RIGHT JOIN, it’s the opposite.


16. Explain a correlated subquery.

Answer: A correlated subquery is a subquery that references columns from the outer query. It executes once for each row processed by the outer query.


17. How do you optimize Join operations?

Answer: To optimize Join operations, ensure proper indexing on Join columns, limit the result set with WHERE clause, and use appropriate Join types based on data distribution.


18. What is the difference between UNION and JOIN?

Answer: UNION is used to combine the result sets of two or more SELECT queries, removing duplicates. JOIN is used to combine rows from two or more tables based on related columns.


19. Can you perform a Join operation on more than two tables?

Answer: Yes, you can perform a Join operation on more than two tables by extending the Join conditions and clauses.


20. How do you choose which Join to use in a query?

Answer: Choose a Join type based on the desired result set. Use INNER JOIN when you only need matching records. Use LEFT, RIGHT, or FULL JOIN when you need non-matching records as well.


21. Explain the concept of a non-equijoin.

Answer: A non-equijoin is a Join condition that uses comparison operators other than equal (=), such as <, >, <=, >=, etc., to link tables based on specific criteria.


22. How can you perform a self-join in SQL?

SELECT e1.employee_name, e2.employee_name
FROM employees e1, employees e2
WHERE e1.manager_id = e2.employee_id;

Answer: In this example, we perform a self-join to retrieve the names of employees and their respective managers.


23. What is the difference between a Join and a Subquery?

Answer: A Join combines rows from different tables, while a Subquery is a query nested within another query. Joins are used to retrieve data from multiple tables, while Subqueries are used to perform operations on individual rows.


24. Explain the concept of a theta join.

Answer: A theta join is a Join operation that uses a theta operator (<=, >=, <, >, <>, !=, =) to link tables based on a specified condition.


25. How do you avoid a Cartesian product when performing a Join?

Answer: To avoid a Cartesian product, always provide a meaningful Join condition that links related columns between tables, ensuring a specific match.


26. What is a semi-join?

Answer: A semi-join is a Join operation that returns only the rows from the first table where a match is found in the second table, without duplicates.


27. What is an anti-join?

Answer: An anti-join is a Join operation that returns only the rows from the first table where no match is found in the second table.


28. Explain the concept of a left anti-semi join.

Answer: A left anti-semi join returns only the rows from the first table where no match is found in the second table, without duplicates.


29. How do you perform a natural join?

SELECT *
FROM employees
NATURAL JOIN departments;

Answer: In this example, we perform a natural join, which automatically matches columns with the same name in both tables.


30. What is a self-anti-join?

Answer: A self-anti-join is a Join operation that returns only the rows from the first instance of the table where no match is found in the second instance.


31. How do you perform a RIGHT JOIN in SQL?

SELECT *
FROM customers
RIGHT JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a RIGHT JOIN to return all records from the right table (orders) and matched records from the left table (customers).


32. How do you perform a FULL JOIN in SQL?

SELECT *
FROM customers
FULL JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a FULL JOIN to return all records when there is a match in one of the tables. It combines the results of both LEFT JOIN and RIGHT JOIN.


33. What is a non-equi join?

Answer: A non-equi join is a Join operation that uses comparison operators other than equal (=) to link tables based on specific criteria, such as <, >, <=, >=, etc.


34. How do you perform a LEFT JOIN with multiple conditions?

SELECT *
FROM customers
LEFT JOIN orders
ON customers.customer_id = orders.customer_id
AND orders.order_status = 'Shipped';

Answer: In this example, we perform a LEFT JOIN with multiple conditions, linking customer IDs and checking for a specific order status.


35. How do you perform a RIGHT JOIN with multiple conditions?

SELECT *
FROM customers
RIGHT JOIN orders
ON customers.customer_id = orders.customer_id
AND orders.order_status = 'Shipped';

Answer: In this example, we perform a RIGHT JOIN with multiple conditions, linking customer IDs and checking for a specific order status.


36. How do you perform a FULL JOIN with multiple conditions?

SELECT *
FROM customers
FULL JOIN orders
ON customers.customer_id = orders.customer_id
AND orders.order_status = 'Shipped';

Answer: In this example, we perform a FULL JOIN with multiple conditions, linking customer IDs and checking for a specific order status.


37. How do you perform a JOIN using the USING clause with multiple columns?

SELECT *
FROM customers
JOIN orders
USING (customer_id, product_id);

Answer: The USING clause can be used with multiple columns to specify a list of columns to join.


38. How do you perform a CROSS JOIN with a WHERE clause?

SELECT *
FROM customers
CROSS JOIN products
WHERE products.category = 'Electronics';

Answer: In this example, we perform a CROSS JOIN with a WHERE clause to filter the result set based on the product category.


39. How do you perform a JOIN with a subquery?

SELECT *
FROM customers
JOIN (
    SELECT customer_id, SUM(order_total) as total_spent
    FROM orders
    GROUP BY customer_id
) order_totals
ON customers.customer_id = order_totals.customer_id;

Answer: In this example, we perform a JOIN with a subquery to get the total amount spent by each customer.


40. How do you perform a self-join with multiple conditions?

SELECT e1.employee_name, e2.employee_name
FROM employees e1, employees e2
WHERE e1.manager_id = e2.manager_id
AND e1.employee_id != e2.employee_id;

Answer: In this example, we perform a self-join with multiple conditions to retrieve employees and their respective managers.


41. How do you perform a Join operation with tables from different databases?

SELECT *
FROM database1.table1
JOIN database2.table2
ON table1.column = table2.column;

Answer: In this example, we perform a Join operation between tables from different databases by fully qualifying the table names.


42. How do you perform a Join with tables from different servers?

SELECT *
FROM server1.database1.table1
JOIN server2.database2.table2
ON table1.column = table2.column;

Answer: In this example, we perform a Join operation between tables from different servers by specifying the server names.


43. How do you handle performance issues related to Joins?

Answer: To address performance issues related to Joins, ensure proper indexing on Join columns, limit the result set with WHERE clause, and use appropriate Join types based on data distribution.


44. What is a self-join with an alias?

SELECT e1.employee_name, e2.employee_name
FROM employees e1, employees e2
WHERE e1.manager_id = e2.employee_id;

Answer: In this example, we perform a self-join with table aliases (e1 and e2) for clarity and readability.


45. How do you perform a Join operation with tables having large datasets?

Answer: When dealing with large datasets, it’s crucial to ensure proper indexing, use efficient Join algorithms, and consider denormalization or summary tables for optimization.


46. Explain the difference between JOIN and UNION.

Answer: JOIN combines rows from different tables based on related columns. UNION combines the result sets of two or more SELECT queries, removing duplicates.


47. How do you perform a Join operation with tables having different collations?

SELECT *
FROM table1
JOIN table2
ON COLLATE database_default = SQL_Latin1_General_CP1_CI_AS
WHERE table1.column = table2.column;

Answer: In this example, we use the COLLATE clause to handle different collations during the Join operation.


48. What is a semi-join with a subquery?

SELECT *
FROM customers
WHERE customer_id IN (
    SELECT DISTINCT customer_id
    FROM orders
    WHERE order_status = 'Shipped'
);

Answer: In this example, we perform a semi-join using a subquery to retrieve customers who have placed at least one shipped order.


49. What is an anti-join with a subquery?

SELECT *
FROM customers
WHERE customer_id NOT IN (
    SELECT DISTINCT customer_id
    FROM orders
    WHERE order_status = 'Shipped'
);

Answer: In this example, we perform an anti-join using a subquery to retrieve customers who have not placed any shipped orders.


50. How do you perform a Join operation on tables with composite keys?

SELECT *
FROM table1
JOIN table2
ON table1.key1 = table2.key1
AND table1.key2 = table2.key2;

Answer: In this example, we perform a Join operation on tables with composite keys, specifying the equality conditions for both keys.


51. How do you handle Join operations on large tables with limited memory?

Answer: Use proper indexing, consider partitioning large tables, and use efficient Join algorithms like Hash Joins or Merge Joins to minimize memory usage.


52. What is a nested Join?

Answer: A nested Join is a Join operation that involves multiple Join conditions and can include multiple tables. It’s also known as a multi-table Join.


53. How do you perform a Join operation on tables with different datatypes?

SELECT *
FROM table1
JOIN table2
ON CAST(table1.column1 AS VARCHAR) = CAST(table2.column2 AS VARCHAR);

Answer: In this example, we perform a Join operation on tables with different datatypes by casting the columns to a common datatype.


54. What is a Join hint in SQL?

Answer: A Join hint is a directive to the SQL optimizer that specifies the Join method to be used for a specific query. It provides control over the Join execution plan.


55. How do you perform a Join operation with an aggregate function?

SELECT customers.customer_id, COUNT(orders.order_id) as order_count
FROM customers
LEFT JOIN orders
ON customers.customer_id = orders.customer_id
GROUP BY customers.customer_id;

Answer: In this example, we perform a Join operation with an aggregate function to count the number of orders for each customer.


56. How do you perform a Join operation with a CASE statement?

SELECT customers.customer_id, 
       CASE 
           WHEN orders.order_total > 1000 THEN 'High Value'
           ELSE 'Low Value'
       END as order_category
FROM customers
LEFT JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a CASE statement to categorize orders based on their total value.


57. What is a Join condition with a NULL value?

Answer: When a Join condition involves a column with NULL values, the comparison (NULL = NULL) will not evaluate to true. Therefore, the Join will not consider NULLs as matching.


58. How do you perform a Join operation with a LIKE operator?

SELECT *
FROM customers
JOIN orders
ON customers.customer_name LIKE CONCAT('%', orders.customer_name, '%');

Answer: In this example, we perform a Join operation using the LIKE operator to match customer names partially.


59. How do you perform a Join operation with a REGEXP pattern?

SELECT *
FROM customers
JOIN orders
ON customers.customer_name REGEXP '^J';

Answer: In this example, we perform a Join operation using a regular expression pattern to match customer names starting with ‘J’.


60. How do you perform a Join operation with a date range?

SELECT *
FROM customers
JOIN orders
ON orders.order_date BETWEEN '2023-01-01' AND '2023-12-31';

Answer: In this example, we perform a Join operation based on a date range using the BETWEEN operator.


61. How do you perform a Join operation with a subquery in the WHERE clause?

SELECT *
FROM customers
JOIN (
    SELECT customer_id, MAX(order_date) as latest_order
    FROM orders
    GROUP BY customer_id
) latest_orders
ON customers.customer_id = latest_orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery in the WHERE clause to retrieve the latest orders for each customer.


62. How do you perform a Join operation with a subquery in the SELECT clause?

SELECT customers.customer_name, (
    SELECT COUNT(*)
    FROM orders
    WHERE orders.customer_id = customers.customer_id
) as order_count
FROM customers;

Answer: In this example, we perform a Join operation with a subquery in the SELECT clause to get the count of orders for each customer.


63. How do you perform a Join operation with a subquery in the FROM clause?

SELECT *
FROM (
    SELECT customer_id, customer_name
    FROM customers
) c
JOIN orders
ON c.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery in the FROM clause to select specific columns before performing the Join.


64. How do you perform a Join operation with a subquery in the HAVING clause?

SELECT customers.customer_id, customers.customer_name
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id
GROUP BY customers.customer_id, customers.customer_name
HAVING COUNT(orders.order_id) > 5;

Answer: In this example, we perform a Join operation with a subquery in the HAVING clause to filter results based on a condition.


65. How do you perform a Join operation with a subquery in the ORDER BY clause?

SELECT customers.customer_id, customers.customer_name
FROM customers
JOIN (
    SELECT customer_id, COUNT(order_id) as order_count
    FROM orders
    GROUP BY customer_id
) order_counts
ON customers.customer_id = order_counts.customer_id
ORDER BY order_counts.order_count DESC;

Answer: In this example, we perform a Join operation with a subquery in the ORDER BY clause to sort the results based on the order count.


  1. How do you perform a Join operation with a subquery that returns multiple columns?
SELECT customers.customer_id, customers.customer_name, order_totals.total_spent
FROM customers
JOIN (
    SELECT customer_id, 
           SUM(order_total) as total_spent,
           COUNT(order_id) as order_count
    FROM orders
    GROUP BY customer_id
) order_totals
ON customers.customer_id = order_totals.customer_id;

Answer: In this example, we perform a Join operation with a subquery that returns multiple columns for each customer.


67. How do you perform a Join operation with a subquery that uses a JOIN itself?

SELECT customers.customer_id, customers.customer_name
FROM customers
JOIN (
    SELECT customer_id, product_id
    FROM orders
    JOIN order_details
    ON orders.order_id = order_details.order_id
) order_products
ON customers.customer_id = order_products.customer_id;

Answer: In this example, we perform a Join operation with a subquery that includes its own Join operation.


68. How do you perform a Join operation with a subquery that uses a correlated subquery?

SELECT customers.customer_id, customers.customer_name
FROM customers
JOIN (
    SELECT customer_id, 
           (SELECT MAX(order_date) FROM orders WHERE orders.customer_id = o.customer_id) as latest_order_date
    FROM orders o
) latest_orders
ON customers.customer_id = latest_orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that includes a correlated subquery to retrieve the latest order date for each customer.


69. How do you perform a Join operation with a subquery that uses a common table expression (CTE)?

WITH recent_orders AS (
    SELECT customer_id, MAX(order_date) as latest_order_date
    FROM orders
    GROUP BY customer_id
)
SELECT customers.customer_id, customers.customer_name, recent_orders.latest_order_date
FROM customers
JOIN recent_orders
ON customers.customer_id = recent_orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a common table expression (CTE) to get the latest order date for each customer.


70. How do you perform a Join operation with a subquery that uses a temporary table?

CREATE TEMPORARY TABLE temp_order_totals AS (
    SELECT customer_id, 
           SUM(order_total) as total_spent
    FROM orders
    GROUP BY customer_id
);

SELECT customers.customer_id, customers.customer_name, temp_order_totals.total_spent
FROM customers
JOIN temp_order_totals
ON customers.customer_id = temp_order_totals.customer_id;

DROP TEMPORARY TABLE IF EXISTS temp_order_totals;

Answer: In this example, we perform a Join operation with a subquery that uses a temporary table to store intermediate results.


71. How do you perform a Join operation with a subquery that uses a table variable?

DECLARE @temp_order_totals TABLE (
    customer_id INT,
    total_spent DECIMAL(10,2)
);

INSERT INTO @temp_order_totals
SELECT customer_id, SUM(order_total)
FROM orders
GROUP BY customer_id;

SELECT customers.customer_id, customers.customer_name, t.total_spent
FROM customers
JOIN @temp_order_totals t
ON customers.customer_id = t.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a table variable to store intermediate results.


72. How do you perform a Join operation with a subquery that uses a user-defined function (UDF)?

CREATE FUNCTION get_order_total(customer_id INT)
RETURNS DECIMAL(10,2)
BEGIN
    RETURN (
        SELECT SUM(order_total)
        FROM orders
        WHERE orders.customer_id = customer_id
    );
END;

SELECT customers.customer_id, customers.customer_name, get_order_total(customers.customer_id) as total_spent
FROM customers;

Answer: In this example, we perform a Join operation with a subquery that uses a user-defined function (UDF) to calculate the order total for each customer.


73. How do you perform a Join operation with a subquery that uses a window function?

SELECT customers.customer_id, customers.customer_name, 
       SUM(order_total) OVER (PARTITION BY customers.customer_id) as total_spent
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a window function to calculate the total spent by each customer.


74. How do you perform a Join operation with a subquery that uses an analytic function?

SELECT customers.customer_id, customers.customer_name, 
       RANK() OVER (ORDER BY orders.order_date DESC) as order_rank
FROM customers
JOIN orders


ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses an analytic function to rank orders by date for each customer.


75. How do you perform a Join operation with a subquery that uses a correlated common table expression (CTE)?

WITH RECURSIVE order_hierarchy AS (
    SELECT order_id, order_parent_id
    FROM orders
    WHERE order_id = @start_order_id
    UNION ALL
    SELECT o.order_id, o.order_parent_id
    FROM orders o
    JOIN order_hierarchy oh
    ON oh.order_parent_id = o.order_id
)
SELECT *
FROM order_hierarchy;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated common table expression (CTE) to retrieve the hierarchy of orders.


76. How do you perform a Join operation with a subquery that uses a correlated view?

CREATE VIEW order_totals AS 
    SELECT customer_id, SUM(order_total) as total_spent
    FROM orders
    GROUP BY customer_id;

SELECT customers.customer_id, customers.customer_name, ot.total_spent
FROM customers
JOIN order_totals ot
ON customers.customer_id = ot.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated view to get the total spent by each customer.


77. How do you perform a Join operation with a subquery that uses a correlated stored procedure?

CREATE PROCEDURE get_order_total(customer_id INT, OUT total_spent DECIMAL(10,2))
BEGIN
    SELECT SUM(order_total) INTO total_spent
    FROM orders
    WHERE orders.customer_id = customer_id;
END;

CALL get_order_total(@customer_id, @total_spent);

SELECT customers.customer_id, customers.customer_name, @total_spent as total_spent
FROM customers;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated stored procedure to get the total spent by each customer.


78. How do you perform a Join operation with a subquery that uses a correlated trigger?

CREATE TRIGGER calculate_order_total
AFTER INSERT ON orders
FOR EACH ROW
BEGIN
    UPDATE customers
    SET total_spent = (
        SELECT SUM(order_total)
        FROM orders
        WHERE orders.customer_id = NEW.customer_id
    )
    WHERE customers.customer_id = NEW.customer_id;
END;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated trigger to update the total spent by each customer after an order is inserted.


79. How do you perform a Join operation with a subquery that uses a correlated user-defined aggregate function?

CREATE AGGREGATE total_order_cost(decimal(10,2))
(
    SFUNC = fn_total_cost,
    STYPE = decimal(10,2),
    INITCOND = '0'
);

CREATE FUNCTION fn_total_cost(a decimal(10,2), b decimal(10,2)) RETURNS decimal(10,2)
    RETURN a + b;

SELECT customers.customer_id, customers.customer_name, 
       total_order_cost(orders.order_total) as total_spent
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated user-defined aggregate function to calculate the total spent by each customer.


80. How do you perform a Join operation with a subquery that uses a correlated cursor?

DECLARE @customer_id INT;
DECLARE @order_total DECIMAL(10,2);

DECLARE order_cursor CURSOR FOR
    SELECT customer_id, SUM(order_total)
    FROM orders
    GROUP BY customer_id;

OPEN order_cursor;

FETCH NEXT FROM order_cursor INTO @customer_id, @order_total;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Perform Join operation using @customer_id and @order_total
    FETCH NEXT FROM order_cursor INTO @customer_id, @order_total;
END;

CLOSE order_cursor;
DEALLOCATE order_cursor;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated cursor to process orders for each customer.


81. How do you perform a Join operation with a subquery that uses a correlated temporary table?

CREATE TEMPORARY TABLE temp_order_totals (
    customer_id INT,
    total_spent DECIMAL(10,2)
);

INSERT INTO temp_order_totals
SELECT customer_id, SUM(order_total)
FROM orders
GROUP BY customer_id;

SELECT customers.customer_id, customers.customer_name, t.total_spent
FROM customers
JOIN temp_order_totals t
ON customers.customer_id = t.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated temporary table to store

intermediate results.


82. How do you perform a Join operation with a subquery that uses a correlated table variable?

DECLARE @temp_order_totals TABLE (
    customer_id INT,
    total_spent DECIMAL(10,2)
);

INSERT INTO @temp_order_totals
SELECT customer_id, SUM(order_total)
FROM orders
GROUP BY customer_id;

SELECT customers.customer_id, customers.customer_name, t.total_spent
FROM customers
JOIN @temp_order_totals t
ON customers.customer_id = t.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated table variable to store intermediate results.


83. How do you perform a Join operation with a subquery that uses a correlated user-defined function (UDF)?

CREATE FUNCTION get_order_total(customer_id INT)
RETURNS DECIMAL(10,2)
BEGIN
    RETURN (
        SELECT SUM(order_total)
        FROM orders
        WHERE orders.customer_id = customer_id
    );
END;

SELECT customers.customer_id, customers.customer_name, get_order_total(customers.customer_id) as total_spent
FROM customers;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated user-defined function (UDF) to calculate the order total for each customer.


84. How do you perform a Join operation with a subquery that uses a correlated window function?

SELECT customers.customer_id, customers.customer_name, 
       SUM(order_total) OVER (PARTITION BY customers.customer_id) as total_spent
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated window function to calculate the total spent by each customer.


85. How do you perform a Join operation with a subquery that uses a correlated analytic function?

SELECT customers.customer_id, customers.customer_name, 
       RANK() OVER (ORDER BY orders.order_date DESC) as order_rank
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated analytic function to rank orders by date for each customer.


86. How do you perform a Join operation with a subquery that uses a correlated recursive common table expression (CTE)?

WITH RECURSIVE order_hierarchy AS (
    SELECT order_id, order_parent_id
    FROM orders
    WHERE order_id = @start_order_id
    UNION ALL
    SELECT o.order_id, o.order_parent_id
    FROM orders o
    JOIN order_hierarchy oh
    ON oh.order_parent_id = o.order_id
)
SELECT *
FROM order_hierarchy;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive common table expression (CTE) to retrieve the hierarchy of orders.


87. How do you perform a Join operation with a subquery that uses a correlated recursive view?

CREATE VIEW order_hierarchy AS 
    SELECT order_id, order_parent_id
    FROM orders
    WHERE order_id = @start_order_id
    UNION ALL
    SELECT o.order_id, o.order_parent_id
    FROM orders o
    JOIN order_hierarchy oh
    ON oh.order_parent_id = o.order_id;

SELECT *
FROM order_hierarchy;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive view to retrieve the hierarchy of orders.


88. How do you perform a Join operation with a subquery that uses a correlated recursive stored procedure?

CREATE PROCEDURE get_order_hierarchy(order_id INT)
BEGIN
    SELECT order_id, order_parent_id
    FROM orders
    WHERE order_id = order_id
    UNION ALL
    SELECT o.order_id, o.order_parent_id
    FROM orders o
    JOIN get_order_hierarchy oh
    ON oh.order_parent_id = o.order_id;
END;

CALL get_order_hierarchy(@start_order_id);

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive stored procedure to retrieve the hierarchy of orders.


89. How do you perform a Join operation with a subquery that uses a correlated recursive trigger?

CREATE TRIGGER calculate_order_hierarchy
AFTER INSERT ON orders
FOR EACH ROW
BEGIN
    INSERT INTO order_hierarchy (order_id, order_parent_id)
    VALUES (NEW.order_id, NEW.order_parent_id);

    IF NEW.order_parent_id IS NOT NULL THEN
        INSERT INTO order_hierarchy (order_id, order_parent_id)
        VALUES (NEW.order_parent_id, NULL);
    END IF;
END;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive trigger to update the hierarchy of orders after an order is inserted.


90. How do you perform a Join operation with a subquery that uses a correlated recursive user-defined aggregate function?

CREATE AGGREGATE get_order_hierarchy(ORDER_TYPE)
(
    SFUNC = fn_get_order_hierarchy,
    STYPE = ORDER_TYPE,
    INITCOND = NULL
);

CREATE FUNCTION fn_get_order_hierarchy(a ORDER_TYPE, b ORDER_TYPE) RETURNS ORDER_TYPE
    RETURN a + b;

SELECT customers.customer_id, customers.customer_name, 
       get_order_hierarchy(orders.order_id) as order_hierarchy
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive user-defined aggregate function to calculate the order hierarchy for each customer.


91. How do you perform a Join operation with a subquery that uses a correlated recursive cursor?

DECLARE @order_cursor CURSOR FOR
    SELECT order_id, order_parent_id
    FROM orders
    WHERE order_id = @start_order_id;

DECLARE @order_id INT;
DECLARE @order_parent_id INT;

OPEN @order_cursor;

FETCH NEXT FROM @order_cursor INTO @order_id, @order_parent_id;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Perform Join operation using @order_id and @order_parent_id
    FETCH NEXT FROM @order_cursor INTO @order_id, @order_parent_id;
END;

CLOSE @order_cursor;
DEALLOCATE @order_cursor;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive cursor to process orders in a hierarchy.


92. How do you perform a Join operation with a subquery that uses a correlated recursive temporary table?

CREATE TEMPORARY TABLE temp_order_hierarchy (
    order_id INT,
    order_parent_id INT
);

INSERT INTO temp_order_hierarchy
SELECT order_id, order_parent_id
FROM orders
WHERE order_id = @start_order_id;

DECLARE @order_id INT;
DECLARE @order_parent_id INT;

DECLARE order_cursor CURSOR FOR
    SELECT order_id, order_parent_id
    FROM temp_order_hierarchy;

OPEN order_cursor;

FETCH NEXT FROM order_cursor INTO @order_id, @order_parent_id;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Perform Join operation using @order_id and @order_parent_id
    FETCH NEXT FROM order_cursor INTO @order_id, @order_parent_id;
END;

CLOSE order_cursor;
DEALLOCATE order_cursor;

DROP TEMPORARY TABLE IF EXISTS temp_order_hierarchy;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive temporary table to process orders in a hierarchy.


93. How do you perform a Join operation with a subquery that uses a correlated recursive table variable?

DECLARE @temp_order_hierarchy TABLE (
    order_id INT,
    order_parent_id INT
);

INSERT INTO @temp_order_hierarchy
SELECT order_id, order_parent_id
FROM orders
WHERE order_id = @start_order_id;

DECLARE @order_id INT;
DECLARE @order_parent_id INT;

DECLARE order_cursor CURSOR FOR
    SELECT order_id, order_parent_id
    FROM @temp_order_hierarchy;

OPEN order_cursor;

FETCH NEXT FROM order_cursor INTO @order_id, @order_parent_id;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Perform Join operation using @order_id and @order_parent_id
    FETCH NEXT FROM order_cursor INTO @order_id, @order_parent_id;
END;

CLOSE order_cursor;
DEALLOCATE order_cursor;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive table variable to process orders in a hierarchy.


94. How do you perform a Join operation with a subquery that uses a correlated recursive user-defined function (UDF)?

CREATE FUNCTION get_order_hierarchy(order_id INT)
RETURNS TABLE (
    order_id INT,
    order_parent_id INT
)
BEGIN
    RETURN (
        WITH RECURSIVE order_hierarchy AS (
            SELECT order_id, order_parent_id
            FROM orders
            WHERE order_id = order_id
            UNION ALL
            SELECT o.order_id, o.order_parent_id
            FROM orders o
            JOIN get_order_hierarchy oh
            ON oh.order_parent_id = o.order_id
        )
        SELECT * FROM order_hierarchy
    );
END;

SELECT customers.customer_id, customers.customer_name, oh.order_id, oh.order_parent_id
FROM customers
JOIN get_order_hierarchy(@start_order_id) oh
ON customers.customer_id = oh.order_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive user-defined function (UDF) to retrieve the hierarchy of orders.


95. How do you perform a Join operation with a subquery that uses a correlated recursive window function?

SELECT customers.customer_id, customers.customer_name, 
       RANK() OVER (PARTITION BY orders.customer_id ORDER BY orders.order_date DESC) as order_rank
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive window function to rank orders by date for each customer.


96. How do you perform a Join operation with a subquery that uses a correlated recursive analytic function?

SELECT customers.customer_id, customers.customer_name, 
       ROW_NUMBER() OVER (PARTITION BY orders.customer_id ORDER BY orders.order_date DESC) as order_row_number
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive analytic function to assign row numbers to orders for each customer.


97. How do you perform a Join operation with a subquery that uses a correlated recursive trigger with a condition?

CREATE TRIGGER calculate_order_hierarchy
AFTER INSERT ON orders
FOR EACH ROW
BEGIN
    IF NEW.order_parent_id IS NOT NULL THEN
        INSERT INTO order_hierarchy (order_id, order_parent_id)
        VALUES (NEW.order_id, NEW.order_parent_id);
    END IF;
END;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive trigger with a condition to update the hierarchy of orders after an order is inserted.


98. How do you perform a Join operation with a subquery that uses a correlated recursive user-defined aggregate function with a condition?

CREATE AGGREGATE get_order_hierarchy(ORDER_TYPE)
(
    SFUNC = fn_get_order_hierarchy,
    STYPE = ORDER_TYPE,
    INITCOND = NULL,
    MSFUNC = fn_get_order_hierarchy_condition,
    MINITCOND = NULL
);

CREATE FUNCTION fn_get_order_hierarchy_condition(a ORDER_TYPE, b ORDER_TYPE) RETURNS ORDER_TYPE
    RETURN IF b IS NOT NULL THEN a + b ELSE a END;

SELECT customers.customer_id, customers.customer_name, 
       get_order_hierarchy(orders.order_id) as order_hierarchy
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive

user-defined aggregate function with a condition to calculate the order hierarchy for each customer.


99. How do you perform a Join operation with a subquery that uses a correlated recursive cursor with a condition?

DECLARE @order_cursor CURSOR FOR
    SELECT order_id, order_parent_id
    FROM orders
    WHERE order_id = @start_order_id
    AND order_parent_id IS NOT NULL;

DECLARE @order_id INT;
DECLARE @order_parent_id INT;

OPEN @order_cursor;

FETCH NEXT FROM @order_cursor INTO @order_id, @order_parent_id;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Perform Join operation using @order_id and @order_parent_id
    FETCH NEXT FROM @order_cursor INTO @order_id, @order_parent_id;
END;

CLOSE @order_cursor;
DEALLOCATE @order_cursor;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive cursor with a condition to process orders in a hierarchy.


100. How do you perform a Join operation with a subquery that uses a correlated recursive temporary table with a condition?

CREATE TEMPORARY TABLE temp_order_hierarchy (
    order_id INT,
    order_parent_id INT
);

INSERT INTO temp_order_hierarchy
SELECT order_id, order_parent_id
FROM orders
WHERE order_id = @start_order_id
AND order_parent_id IS NOT NULL;

DECLARE @order_id INT;
DECLARE @order_parent_id INT;

DECLARE order_cursor CURSOR FOR
    SELECT order_id, order_parent_id
    FROM temp_order_hierarchy;

OPEN order_cursor;

FETCH NEXT FROM order_cursor INTO @order_id, @order_parent_id;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- Perform Join operation using @order_id and @order_parent_id
    FETCH NEXT FROM order_cursor INTO @order_id, @order_parent_id;
END;

CLOSE order_cursor;
DEALLOCATE order_cursor;

DROP TEMPORARY TABLE IF EXISTS temp_order_hierarchy;

Answer: In this example, we perform a Join operation with a subquery that uses a correlated recursive temporary table with a condition to process orders in a hierarchy.