What's the most efficient way to perform this query on a CoreData table? To use the standard employees database model -- I want DISTINCT department ID's for all departments that contain employees with job-description "chef." As it happens, there is only a single table (Employees) relevant here -- I don't actually have a departments table, just department ID's that are repeated.What's the most efficient way to perform this q
阅读背景：
获取核心数据中不同的ID列表
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