如何查找MySQL查询结果中两行的差异

我有以下MySQL查询：

SET @rowno= 0;
SELECT @rowno:=@rowno+1 AS `row`,`year`,`year_average` FROM(
/*get the average from the start of the 10 year period and the current period*/  

SELECT year,AVG(value) AS year_average FROM
/* get all records that have technical and trade school industry code */
(SELECT * FROM `allcesseries`
   WHERE series_id LIKE concat('%',(SELECT industry_code FROM `ceindustry` WHERE industry_name LIKE      '%Technical and trade schools%'),'%')) AS trade_schools
WHERE trade_schools.year = (2014-10) OR trade_schools.year = 2014
GROUP BY year) AS t

返回值

row | year | year_average
 1    2004   76.24
 2    2014   99.9

我似乎不知道如何获得第一行的年平均值和第二行的年平均值之间的差异。

使用MySQL

SELECT (
  (SELECT AVG(value)
  FROM allcesseries
  WHERE series_id LIKE concat('%',(SELECT industry_code FROM `ceindustry` WHERE industry_name LIKE '%Technical and trade schools%'),'%')
    AND year = 2014)
  -
  (SELECT AVG(value)
  FROM allcesseries
  WHERE series_id LIKE concat('%',(SELECT industry_code FROM `ceindustry` WHERE industry_name LIKE '%Technical and trade schools%'),'%')
    AND year = 2004)
) AS difference
;

应该有用。看见如果在您的情况下不起作用（或需要调整），请提供表结构和示例数据