Parent Relationship Queries

List<Contact> contacts = [
    SELECT Id, LastName, Account.Name, Account.Industry
    FROM Contact
];

for (Contact con : contacts) {
    System.debug(con.LastName + ' works at ' + con.Account.Name);
}

This is Module 18's "Relationships in Apex" lesson from the query side: Account.Name and Account.Industry in the SELECT clause pull the parent Account's fields into the same query result — no second query needed to fetch them separately.

List<Contact> contacts = [
    SELECT Id, LastName, Account.Owner.Name
    FROM Contact
];

Account.Owner.Name reaches two levels up: from Contact to its parent Account, and from that Account to its owning User's Name. Salesforce supports traversing up to 5 relationship levels deep in a single SOQL query this way.

// DON'T DO THIS — a query inside a loop
for (Contact con : contacts) {
    Account acc = [SELECT Name FROM Account WHERE Id = :con.AccountId]; // a query per contact!
}

This is exactly the SOQL-in-a-loop governor limit problem revisited from Module 18. A single query with Account.Name in the SELECT clause retrieves everything needed up front, entirely avoiding the per-record query that would otherwise blow past governor limits at scale.