/*獲取id值與5相減絕對值最近的數(shù)據(jù),如果有絕對值相同的,相鄰的數(shù)據(jù)優(yōu)先輸出*/
/*ABS(X)其實(shí)就是獲取絕對值，然后的話order by 后面的1代表著根據(jù)select關(guān)鍵字
后的第一個字段進(jìn)行排序。limit 后面的數(shù)字代表著你想查詢數(shù)據(jù)的行數(shù)*/
SELECT ABS(cid-5),cname FROM company ORDER BY 1 LIMIT 3

/*獲取指定id的上一條記錄，我這里是以id=5為例的*/
select cid,cname from company order by cid>=5,cid desc limit 1

/*獲取指定id的下一條記錄，我這里是以id=5為例的*/
SELECT cid,cname from company order by cid<=5,cid asc limit 1

記錄一下，以免以后遇到又不會

同表相鄰數(shù)據(jù)比對查詢

需求

我們將會比對相鄰的數(shù)據(jù)，其中value是遞增的，但也會存在清零的情況。我們的需求是計算當(dāng)天的分鐘遞增量。

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SQL

語句中需要解釋一下參數(shù)

** ctc_etl.1_1_1907/sum.out_2021 ：表名**** WHERE
item_timestamp > “2021-12-01 00:00:00”
AND item_timestamp < “2021-12-02 00:00:00” 是我自己加的篩選條件**

SELECT b.id,( b.item_value - a.item_value ) AS value,
	b.item_timestamp AS time 
FROM
	(
	SELECT id,item_value,
		@num := @num + 1 AS row_number 
	FROM
		( SELECT @num := 0 ) r,
			ctc_etl.`1_1_1907/sum.out_2021` 
	WHERE
		item_timestamp > "2021-12-01 00:00:00" 
		AND item_timestamp < "2021-12-02 00:00:00" 
	ORDER BY
		id 
	) a,
	(
	SELECT
		id,
		item_value,
		item_timestamp,
		@num2 := @num2 + 1 AS row_number 
	FROM
		( SELECT @num2 := 0 ) r2,
			ctc_etl.`1_1_1907/sum.out_2021` 
	WHERE
		item_timestamp > "2021-12-01 00:00:00" 
		AND item_timestamp < "2021-12-02 00:00:00" 
	ORDER BY
		id 
	) b 
WHERE
	a.row_number + 1 = b.row_number;

解析

目前計算的只是每秒的增加量，其次就是存在負(fù)數(shù)的情況，也就是清零了后一個數(shù)比前一個小就造成了負(fù)數(shù)

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最終SQL

SELECT
	c.id,
	SUM( c.VALUE ) AS value,
	DATE_FORMAT( c.time, "%Y-%m-%d %H:%i:00" ) AS time 
FROM
	(
	SELECT
		b.id,
		(b.item_value - a.item_value ) AS value,
		b.item_timestamp AS time 
	FROM
		(
		SELECT
			id,
			item_value,
			@num := @num + 1 AS row_number 
		FROM
			( SELECT @num := 0 ) r,
			ctc_etl.`1_1_1907/sum.out_2021` 
		WHERE
			item_timestamp > "2021-12-01 00:00:00" 
			AND item_timestamp < "2021-12-02 00:00:00" 
		ORDER BY
			id 
		) a,
		(
		SELECT
			id,
			item_value,
			item_timestamp,
			@num2 := @num2 + 1 AS row_number 
		FROM
			( SELECT @num2 := 0 ) r2,
			ctc_etl.`1_1_1907/sum.out_2021` 
		WHERE
			item_timestamp > "2021-12-01 00:00:00" 
		AND item_timestamp < "2021-12-02 00:00:00" ORDER BY id ) b WHERE a.row_number + 1 = b.row_number ) c WHERE c.VALUE > 0 
GROUP BY
	DATE_FORMAT(
	c.time,
	"%Y-%m-%d %H:%i:00")

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