Question

我有以下查询;

SELECT count(*) as aggregate 
FROM cars
INNER JOIN snapshots ON cars.snapshot_id=snapshots.id
WHERE cars.snapshot_id=194340

正常工作 - 使用特定的snapshot_id计算所有汽车。

但是现在我只想计算从创建快照到那里过去1小时以上的汽车。

我试过这个 - 但它不起作用：

SELECT count(*) as aggregate 
FROM cars
INNER JOIN snapshots ON cars.snapshot_id=snapshots.id
WHERE cars.snapshot_id=194340
AND time_arrive_destination <= DATE_SUB('snapshots.created_at', INTERVAL 1 HOUR)

我知道我已经关闭了 - 因为如果我对来自snapshots.created_at的时间戳进行硬编码 - 就可以了：

SELECT count(*) as aggregate 
FROM cars
INNER JOIN snapshots ON cars.snapshot_id=snapshots.id
WHERE cars.snapshot_id=194340
AND time_arrive_destination <= DATE_SUB("2015-08-31 20:29:49", INTERVAL 1 HOUR)

那么如何将加入的列字段snapshots.created_at用作date_sub()的变量？

Answer 1

如果您需要（或想要）转义标识符（例如列名，因为它是保留字），请将标识符用反引号字符括起来，而不是单引号，例如

AND time_arrive_destination <= DATE_SUB(`snapshots`.`created_at`, INTERVAL 1 HOUR)

使用join field作为date_sub的变量

1 个答案: