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SQL Study Questions

  1. What is SQL and what is used for?

    • SQL stands for Structured Query Language, and is used for interacting with data in a relational database.

  2. What does CRUD stand for, and what are some keywords/SQL syntax that go along with such actions?

    • CRUD stands for Create, Read, Update and Delete.
    • Create: INSERT INTO table VALUES (column1, column2, ...) SET (value1, value2, …);
    • Read: SELECT column1, column2, … FROM table;
    • Update: UPDATE table SET column=value WHERE …;
    • Delete: DELETE FROM table WHERE …;

  3. Write a SQL expression for the following diagram (Everything in A that is not in B, i.e. a Left Excluding Join)

    SELECT * FROM A
    LEFT JOIN B on B.A_ID = A.ID
    WHERE B.A_ID IS NULL;

  4. When should you add an index to a database column? What is the cost of a database index?

    • When you want to read from the database faster. The cost is that it takes more time to write information to the database

  5. You have a table called drivers and a table called orders. Orders are delivered by drivers. In this way, the orders belong to a driver through the column orders.driver_id. Write a SQL expression that gets all the drivers that have delivered an order.

    SELECT * FROM drivers
    INNER JOIN orders on
    orders.driver_id = driver.id;

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