Implement an in-memory SQL-like table
Company: Valon Mortgage
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: hard
Interview Round: Technical Screen
Implement a simplified in-memory SQL-like database for a single table.
You should support the following operations on a table with a fixed schema (a list of column names). Each row is a mapping from column name to value (you may assume values are strings or integers and can be compared).
Requirements:
1. **INSERT**: Insert a row providing a value for each column.
2. **SELECT with projection**: Return rows while selecting only a specified subset of column names (e.g., `SELECT colA, colC`).
3. **Filtering**: Support a `WHERE` clause that filters rows by a condition on a column (at minimum, equality like `colX = value`; if you choose, you may support additional comparisons).
4. **Ordering**: Support `ORDER BY <column>` (ascending; optionally support descending).
Clarify/handle:
- Invalid column names in SELECT/WHERE/ORDER BY.
- Rows with missing columns (if disallowed, validate on insert).
- Output format: a list of projected rows in the final order.
Design an API (e.g., `insert(row)`, `select(columns, where_clause, order_by)` or parse SQL strings if preferred) and implement the functionality efficiently for typical interview constraints (up to tens or hundreds of thousands of rows).
Quick Answer: This question evaluates implementation-level skills for in-memory data structures and basic query processing, including projection, filtering, ordering, API design, input validation, and algorithmic efficiency.