CROSS JOIN behavior in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from both tables using CROSS JOIN.

PostgreSQL

SELECT * FROM table1 [1] table2;

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ACROSS JOIN

BINNER JOIN

CLEFT JOIN

DRIGHT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN instead of CROSS JOIN.

Forgetting that CROSS JOIN does not need an ON clause.

The CROSS JOIN returns the Cartesian product of rows from both tables.

2fill in blank

medium

Complete the code to count the total number of rows after a CROSS JOIN between two tables.

PostgreSQL

SELECT COUNT(*) FROM tableA [1] tableB;

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AFULL JOIN

BINNER JOIN

CLEFT JOIN

DCROSS JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN which filters rows.

Using FULL JOIN which includes NULLs.

CROSS JOIN returns all combinations of rows, so counting rows after CROSS JOIN gives the product of row counts.

3fill in blank

hard

Fix the error in the query to correctly perform a CROSS JOIN between employees and departments.

PostgreSQL

SELECT employees.name, departments.name FROM employees [1] departments;

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AINNER JOIN

BCROSS JOIN

CLEFT JOIN

DRIGHT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using ON clause with CROSS JOIN.

Confusing CROSS JOIN with INNER JOIN.

CROSS JOIN does not use an ON clause. Remove the ON condition to fix the error.

4fill in blank

hard

Fill both blanks to create a query that selects all pairs of product and color using CROSS JOIN and orders by product name.

PostgreSQL

SELECT products.name, colors.name FROM products [1] colors ORDER BY products.[2];

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ACROSS JOIN

BINNER JOIN

Cname

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN instead of CROSS JOIN.

Ordering by a wrong column.

Use CROSS JOIN to combine all products and colors. Order by the product name.

5fill in blank

hard

Fill all three blanks to create a query that selects employee names, department names, and their combined count using CROSS JOIN and GROUP BY.

PostgreSQL

SELECT employees.[1], departments.[2], COUNT(*) FROM employees [3] departments GROUP BY employees.name, departments.name;

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Aname

Bdepartment_name

CCROSS JOIN

DINNER JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN instead of CROSS JOIN.

Selecting wrong column names.

Select employee name and department department_name. Use CROSS JOIN to combine all pairs and count them.