mysql滑动聚合/年初至今聚合原理与用法实例分析

SELECT
 a.empid,
 DATE_FORMAT(a.ordermonth, '%Y-%m') AS ordermonth,
 a.qty AS thismonth,
 SUM(b.qty) AS total,
 CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avg
FROM emporders a
INNER JOIN emporders b
 ON a.empid=b.empid
 AND b.ordermonth > DATE_ADD(a.ordermonth, INTERVAL -3 MONTH)
 AND b.ordermonth <= a.ordermonth
WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'
GROUP BY a.empid,DATE_FORMAT(a.ordermonth, '%Y-%m'),a.qty
ORDER BY a.empid,a.ordermonth

SELECT
 a.empid,
 a.ordermonth AS ordermonth,
 a.qty AS thismonth,
 SUM(b.qty) AS total,
 CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avg
FROM emporders a
INNER JOIN emporders b
 ON a.empid=b.empid
 AND b.ordermonth > DATE_ADD(a.ordermonth, INTERVAL -3 MONTH)
 AND b.ordermonth <= a.ordermonth
WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015' AND a.empid=1
GROUP BY a.empid,DATE_FORMAT(a.ordermonth, '%Y-%m'),a.qty
HAVING MIN(b.ordermonth)=DATE_ADD(a.ordermonth, INTERVAL-2 MONTH)
ORDER BY a.empid,a.ordermonth

SELECT
 a.empid,
 DATE_FORMAT(a.ordermonth, '%Y-%m') AS ordermonth,
 a.qty AS thismonth,
 SUM(b.qty) AS total,
 CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avg
FROM emporders a
INNER JOIN emporders b
  ON a.empid=b.empid
  AND b.ordermonth >= DATE_FORMAT(a.ordermonth, '%Y-01-01')
  AND b.ordermonth <= a.ordermonth
  AND DATE_FORMAT(b.ordermonth,'%Y')='2015'
GROUP BY a.empid,a.ordermonth,a.qty
ORDER BY a.empid,a.ordermonth