该解决方案将执行累积和，并在超过1000时停止：
SELECt NULL AS users_count, NULL AS total FROM dual WHERe (@total := 0) UNIOnSELECt users_count, @total := @total + users_count AS total FROM messages_queue WHERe @total < 1000;
这意味着，如果您有两个值（例如800），则总和将为1600。第一个SELECt只是初始化
@total变量。
如果要防止总和超过1000（除了单行的值大于1000的情况），那么我认为这是可行的，尽管您需要对其进行严格的测试：
SELECT NULL AS users_count, NULL AS total, NULL AS found FROM dual WHERe (@total := 0 OR @found := 0) UNIOnSELECt users_count, @total AS total, @found := 1 AS found FROM messages_queue WHERe (@total := @total + users_count) AND @total < 1000 UNIOnSELECt users_count, users_count AS total, 0 AS found FROM messages_queue WHERe IF(@found = 0, @found := 1, 0);
