Set operation column matching rules in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all unique names from two tables using UNION.

SQL

SELECT name FROM employees UNION SELECT [1] FROM managers;

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Aname

Bsalary

Cid

Ddepartment

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting different columns in each SELECT statement causes errors.

Using columns with incompatible data types.

The UNION operation requires the columns to match by position and type. Here, both SELECT statements must select the 'name' column.

2fill in blank

medium

Complete the code to combine salaries from two tables using UNION ALL.

SQL

SELECT salary FROM full_time UNION ALL SELECT [1] FROM part_time;

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Ahours

Bname

Csalary

Dposition

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting different columns causes errors.

Using UNION instead of UNION ALL when duplicates are needed.

UNION ALL combines all rows including duplicates. Both SELECT statements must select the 'salary' column to match.

3fill in blank

hard

Fix the error in the set operation by choosing the correct column to match.

SQL

SELECT id, name FROM customers INTERSECT SELECT [1], name FROM orders;

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Aname

Bid

Ccustomer_id

Dorder_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using columns with different data types or meanings.

Mismatching the number of columns in SELECT statements.

Both SELECT statements must have the same number of columns and compatible types in the same order. Here, 'id' matches the first column.

4fill in blank

hard

Fill both blanks to correctly combine product names and prices from two tables using UNION.

SQL

SELECT [1], [2] FROM products_a UNION SELECT product_name, price FROM products_b;

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Aproduct_name

Bprice

Cname

Dcost

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting columns with incompatible data types.

Mismatching the order of columns.

The first SELECT must select columns that match the second SELECT by position and type. 'name' matches 'product_name' in type, and 'price' matches 'price'.

5fill in blank

hard

Fill all three blanks to correctly perform a UNION of employee details with matching columns.

SQL

SELECT [1], [2], [3] FROM staff UNION SELECT emp_name, emp_salary, emp_dept FROM employees;

Drag options to blanks, or click blank then click option'

Aname

Bsalary

Cdepartment

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using columns with different meanings or data types.

Mismatching the number of columns.

Each column in the first SELECT must match the corresponding column in the second SELECT by position and type. Here, 'name' matches 'emp_name', 'salary' matches 'emp_salary', and 'department' matches 'emp_dept'.