关联行数不等的表并使用SUM函数时，如何获取全部数据？

Hey there! Let’s work through this to get you the exact results you need without that slow, logically shaky workaround you’ve been dealing with. Since TableA and TableB are both derived from larger datasets, the key to fixing this is locking in a few critical details first:

• Spell out your expected outcome clearly: Are you after rows that exist in both tables? Rows unique to TableA? Do you need to combine specific fields with strict filters? The more concrete you are (e.g., "I need all customer IDs from TableA that don’t appear in TableB, paired with their 2024 order totals"), the easier it is to craft a precise, correct query.
• Share your current SQL: Post the exact SELECT statement you’re running now, plus a quick breakdown of how its output misses the mark. For example: "My current query returns 1,200 rows, but I only need 300 that have a status of 'active'."
• Add table structure context: Let us know key details about TableA and TableB—like primary key columns, any existing indexes, and roughly how many rows each table holds. This helps us optimize the query for speed right out the gate.
• Show your previous workaround: If you can share the problematic query you tried (the one that’s logically off and slow), we can break down why it’s underperforming and fix its core logic.

Once you add these details, we can put together a clean, efficient SQL query that gets you exactly the results you’re aiming for.

内容的提问来源于stack exchange，提问作者Josh Wiltgen