Extract the first 3 characters of each user name.
Problem Statement
<p>Extract the first 3 characters of each user name.</p>
Examples
Input: users table: +----+---------+ | id | name | +----+---------+ | 1 | Alice | | 2 | Bob | | 3 | Charlie | +----+---------+
Output: +------------+ | short_name | +------------+ | Ali | | Bob | | Cha | +------------+
Explanation: Only records matching the specified criteria are returned in the final result.
Complexity
Time Complexity: -
Space Complexity: -
Hints
š” Hint 1:
Identify the filtering conditions needed to isolate the target rows from the table.
š” Hint 2:
Use appropriate operators: = for exact matches, LIKE for wildcard patterns, IN for sets, or BETWEEN for numeric/date ranges.
š” Hint 3:
Combine filters with AND/OR if multiple conditions exist: SELECT <cols> FROM <table> WHERE <condition>;
Editorial & Approach
Problem Overview & Intuition
To solve "SUBSTRING Function", we query the relational database engine using declarative SQL. The goal is to extract the first 3 characters of each user name. 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 SUBSTRING(name FROM 1 FOR 3) AS short_name FROM users;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.