How Salesforce Executes a SOQL Query

When a SOQL query runs, Salesforce roughly works through:

1. Parsing — the query text is checked for valid syntax.
2. Permission and sharing checks — which records the running user is even allowed to see (covered in depth in a later Security module).
3. Query optimization — the platform's optimizer decides the fastest way to actually retrieve matching rows, favoring indexed fields when the WHERE clause allows it.
4. Execution — the underlying database retrieves the matching rows.
5. Returning results — rows are converted into sObject records and handed back to Apex as a List.

Step 3 is exactly where the previous lesson's "selectivity" concept becomes concrete: the optimizer can only take the fast, indexed path when the query's WHERE clause actually allows it. A non-selective query forces the optimizer into a slower, broader scan — the direct cause of the timeout risk discussed previously.

List<Account> accounts = [SELECT Id, Name FROM Account]; // respects sharing by default

Step 2 means a plain SOQL query, by default, only returns records the currently running user actually has permission to see — two different users running the exact same query line can get different results. This default behavior (and how to deliberately override it) is covered fully in the upcoming Security module — this lesson's job is just to place it correctly in the overall sequence.