## Round 1 - Coding / SQL ## Problem Implement an in-memory SQL execution engine that parses and executes simple SQL queries over Python dictionaries acting as tables. Support `SELECT`, `FROM`, `WHERE`, and `INNER JOIN`. ```python class SQLEngine: def __init__(self): self.tables: dict[str, list[dict]] = {} def create_table(self, name: str, rows: list[dict]) -> None: ... def execute(self, query: str) -> list[dict]: # parses and runs the SQL query string ... ``` ## Example ``` engine = SQLEngine() engine.create_table("users", [{"id":1,"name":"Alice"},{"id":2,"name":"Bob"}]) engine.create_table("orders", [{"user_id":1,"item":"Book"},{"user_id":1,"item":"Pen"},{"user_id":2,"item":"Bag"}]) engine.execute("SELECT name, item FROM users JOIN orders ON users.id = orders.user_id WHERE name = 'Alice'") # -> [{"name":"Alice","item":"Book"},{"name":"Alice","item":"Pen"}] engine.execute("SELECT * FROM users WHERE id > 1") # -> [{"id":2,"name":"Bob"}] ``` ## Follow-ups 1. How do you tokenize and parse the SQL string without an external parser library? 2. How would you add support for `GROUP BY` and aggregation functions like `COUNT` and `SUM`? 3. How do you handle column name ambiguity when both tables have a column with the same name? 4. What optimizations would you apply (e.g., predicate pushdown, hash join) as table sizes grow?

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SQL Execution Engine: Build a Mini SQL Interpreter Supporting SELECT, WHERE, and JOIN

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Round 1 - Coding / SQL Problem Implement an in-memory SQL execution engine that parses and executes simple SQL queries over Python dictionaries acting as tables. Support SELECT, FROM, WHERE, and INNER JOIN. Example Follow-ups How do you tokenize and parse the SQL string without an external parser library? How would you add support for GROUP BY and aggregation functions like COUNT and SUM? How do you handle column name ambiguity when both tables have a column with the same name? What optimization…

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This is a candidate experience report from a retool interview during the onsite round.

It covers the following topics: Coding, Sql, Onsite, Strings .

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Coding Sql Onsite Strings

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