library(dplyr) unite(mtcars, "vs_am", vs, am) Merging Data Adding Columns To merge two data frames (datasets) horizontally, use the merge function. In most cases, you join two data frames by one or more common key variables (i.e., an inner joi
-- 查询一个数据库表中的索引及索引列use [RuPengWangDB]GOSELECT indexname = a.name , tablename = c. name , indexcolumns = d .name , a .indidFROM sysindexes a JOIN sysindexkeys b ON a .id = b .id AND a .indid = b.indid JOIN sysobjects c ON b .id = c .id
), qy ), je INT); INSERT INTO @t SELECT '产品一', '北京', UNION ALL SELECT '产品一', '上海', UNION ALL SELECT '产品二', '北京', UNION ALL SELECT '产品三', '上海', UNION ALL SELECT '产品三', '北京', UNION ALL SELECT '产品四', '上海', ; SELECT * FROM @t; SELECT * FROM @t a WHERE NO
查询出数据 SELECT a.ID AS KYMain_ID , ',' + a.Leader + ',' AS KYMain_Leader , ), b.TaskLeader) FROM TB_KYChildProject b WHERE b.MainProjectID = a.ID ) FOR XML PATH('') ), , , '') + ',' AS KYChild_Leader , ), b.Single_Leader) FROM TB_KYSubProject b WHERE b
问题: 使用forecast.Arima对带xreg的arima模型进行预测,报xreg Error pre.m4x <- forecast.Arima(m4x, h = 20, xreg = seq(429,448,by = 1)) 报错: Error in if (ncol(xreg) != ncol(object$call$xreg)) stop("Number of regressors does not match fitted model") : argument i
首先描述问题,student表中有字段startID,endID.garde表中的ID需要对应student表中的startID或者student表中的endID才能查出grade表中的name字段,这时候问题就来了,如果需要一条sql一句同时查出garde表中的两条数据怎么办?(两表的关联字段为 SID) sql="select b.name,c.name as name2 from student a,garde b,grade c where a.SID=b.SID and a.SID=c
数据表是这样的 select * from water_level_records m where ( select count(*) from water_level_records n where m.device_id = n.device_id and m.record_time < n.record_time ) 这个sql的逻辑是把一个表当做两个表关联来使用,当满足m的记录时间小于n的记录时间的数量<1 即只有一个相等时返回,即是时间的最大值, 如果为<2 则是为前两大的值,
需求:取stock表中id最大值+1,作为下一个id值. 特殊情况:考虑到表中会没有值,max(id)会返回空,因此需要用case when进行判断. 实现一:select (case max(id) is null when true then 0 else max(id)+1 end) from stock 实现二:select (case (select count(*) from stock) when 0 then 0 else max(id)+1 end) from stock 效率