以下是代码：

CREATE OR REPLACE FUNCTION enforce_photo_count() RETURNS trigger AS $$
DECLARE
    max_photo_count INTEGER := 10;
    photo_count INTEGER := 0;
    must_check BOOLEAN := false;
BEGIN
    IF TG_OP = 'INSERT' THEN
        must_check := true;
    END IF;
 
    IF TG_OP = 'UPDATE' THEN
        IF (NEW.owner != OLD.owner) THEN
            must_check := true;
        END IF;
    END IF;
 
    IF must_check THEN
        -- prevent concurrent inserts from multiple transactions
        LOCK TABLE photos IN EXCLUSIVE MODE;
 
        SELECT INTO photo_count COUNT(*) 
        FROM photos 
        WHERE owner = NEW.owner;
 
        IF photo_count >= max_photo_count THEN
            RAISE EXCEPTION 'Cannot insert more than % photos for each user.',max_photo_count;
        END IF;
    END IF;
 
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;
 
 
CREATE TRIGGER enforce_photo_count 
    BEFORE INSERT OR UPDATE ON photos
    FOR EACH ROW EXECUTE PROCEDURE enforce_photo_count();

我包括表锁定，以避免两个并发的篡改对用户计数照片的情况，看到当前的计数是低于限制的1，然后两者都插入，这将导致你超过限制。如果这不是您的问题，最好删除锁定，因为它可能成为许多插入/更新的瓶颈。