This query shows how to use the PostgreSQL UPDATE join syntax to update data in a table based on values in another table. for example;
updating subscription_missions.giftbox_type with rewards.gift_box_type through mission_rewards table (tested on 300k records, crazy level fast)
UPDATE subscription_missions sm SET giftbox_type = r.gift_box_type FROM mission_rewards mr, rewards r WHERE sm.giftbox_type IS NULL AND sm.id = mr.subscription_mission_id AND mr.reward_id = r.id;
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