Combine names from `students` and `teachers` using UNION ALL, keeping duplicates.

Problem Statement

<p>Combine names from <code>students</code> and <code>teachers</code> using UNION ALL, keeping duplicates.</p>

Examples

Input: students table: +-------+ | name | +-------+ | Alice | | Bob | +-------+ teachers table: +---------+ | name | +---------+ | Bob | | Charlie | +---------+

Output: +---------+ | name | +---------+ | Alice | | Bob | | Bob | | Charlie | +---------+

Explanation: The query retrieves the requested records satisfying all problem requirements.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Combine the results of two or more queries using UNION ALL (preserves duplicates). 💡 Hint 2: Ensure both SELECT queries have the same number of columns in the same order and compatible data types. 💡 Hint 3: Structure: SELECT ... FROM table1 UNION [ALL] SELECT ... FROM table2;

Editorial & Approach

Problem Overview & Intuition

To solve "UNION ALL (With Duplicates)", we query the relational database engine using declarative SQL. The goal is to combine names from `students` and `teachers` using union all, keeping duplicates. By formulating an optimal execution plan with appropriate projection and filtering, the database engine executes the query with minimal overhead.

Step-by-Step Approach

Analyze Schema: Identify the target tables, necessary foreign keys, and expected output columns.
Construct Filtering & Logic: Apply row projections to isolate the requested data.
Format & Order: Ensure columns match the expected project schema in order.

Optimal Implementation (SQL)

SELECT name FROM students UNION ALL SELECT name FROM teachers;

Complexity Analysis

Time Complexity O(N)

Space Complexity O(1)

Key Considerations & Edge Cases

Empty Tables: The query executes safely returning zero rows without syntax error.
NULL Values: Columns containing NULL values are properly handled by standard ANSI SQL semantics.
Case Sensitivity: String comparisons and keywords adhere to PostgreSQL/standard SQL rules.

UNION ALL (With Duplicates)

Medium

Combine names from students and teachers using UNION ALL, keeping duplicates.

Example Scenarios

1Example 1

Input:

students table

name
Alice
Bob

teachers table

name
Bob
Charlie

Output:

name
Alice
Bob
Bob
Charlie

Explanation:

The query retrieves the requested records satisfying all problem requirements.

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