sql - LIMIT 1的替代方案，以提取日期范围以及前后的第一个条目？

Question

基本上，我想在一个范围内+在此之后输入1，在之前输入1。

我这样尝试过：

SELECT DateTime, value FROM ReadingGlucoseBlood WHERE DateTime BETWEEN '2011-01-21 00:00:00' AND datetime('2011-01-21 00:00:00', '+24 hours') 
UNION 
SELECT DateTime, value FROM ReadingGlucoseBlood WHERE DateTime < '2011-01-21 00:00:00' LIMIT 1
UNION
SELECT DateTime, value FROM ReadingGlucoseBlood WHERE DateTime > datetime('2011-01-21 00:00:00', '+24 hours') LIMIT 1
ORDER BY DateTime ASC

但是事实证明，在复合SELECT语句的末尾只能有一个LIMIT。那么如何实现这种效果？ （使用sqlite btw）

Answer 1

您需要对LIMIT进行子查询以限制其范围

SELECT DateTime, value FROM ReadingGlucoseBlood WHERE DateTime BETWEEN '2011-01-21 00:00:00' AND datetime('2011-01-21 00:00:00', '+24 hours') 
UNION ALL
SELECT * FROM (
SELECT DateTime, value FROM ReadingGlucoseBlood WHERE DateTime < '2011-01-21 00:00:00'
ORDER BY DateTime DESC LIMIT 1
) X
UNION ALL
SELECT * FROM (
SELECT DateTime, value FROM ReadingGlucoseBlood WHERE DateTime > datetime('2011-01-21 00:00:00', '+24 hours')
ORDER BY DateTime ASC LIMIT 1
) Y
ORDER BY DateTime ASC