Что выполняется раньше: оператор WHERE или оператор JOIN?

The FROM operator (including JOIN) defines the data sources. The WHERE operator is executed after FROM to filter rows from the combined sources.

The logical order of executing an SQL query:

1. FROM: Defines data sources and performs joins.
2. WHERE: Filters rows obtained from FROM.
3. GROUP BY: Groups rows.
4. HAVING: Filters groups.
5. SELECT: Selects columns.
6. ORDER BY: Sorts the resulting rows.
7. LIMIT/OFFSET: Limits the number of rows.

The JOIN operator is essentially part of the FROM phase.