被遗忘的R中的sql语句

本文主要介SQL在R语言中的应用，很多人将SQL遗忘，在利用R的时候，特别是当工具繁多的时候，R中也有不用连接数据库来练习SQL语句。

1.安装sqldf（）包

install.packages("sqldf")

sqldf(sqldf)

sqldf()所属R语言包：sqldf

SQL select on data frames

SQL选择的数据框

2.采用内部数据集开始练习。

###下面是一段R代码####
library(sqldf)
## Warning: package 'sqldf' was built under R version 3.2.4
## Loading required package: gsubfn
## Warning: package 'gsubfn' was built under R version 3.2.4
## Loading required package: proto
## Loading required package: RSQLite
## Warning: package 'RSQLite' was built under R version 3.2.4
## Loading required package: DBI
## Warning: package 'DBI' was built under R version 3.2.4
data("mtcars")
#mtcars
colnames(mtcars)
##  [1] "mpg"  "cyl"  "disp" "hp"   "drat" "wt"   "qsec" "vs"   "am"   "gear"
## [11] "carb"
sqldf('select * from mtcars where "hp" > 200 ')
## Loading required package: tcltk
##    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## 1 14.3   8  360 245 3.21 3.570 15.84  0  0    3    4
## 2 10.4   8  472 205 2.93 5.250 17.98  0  0    3    4
## 3 10.4   8  460 215 3.00 5.424 17.82  0  0    3    4
## 4 14.7   8  440 230 3.23 5.345 17.42  0  0    3    4
## 5 13.3   8  350 245 3.73 3.840 15.41  0  0    3    4
## 6 15.8   8  351 264 4.22 3.170 14.50  0  1    5    4
## 7 15.0   8  301 335 3.54 3.570 14.60  0  1    5    8
sqldf('select mpg from mtcars where "vs"= 1')
##     mpg
## 1  22.8
## 2  21.4
## 3  18.1
## 4  24.4
## 5  22.8
## 6  19.2
## 7  17.8
## 8  32.4
## 9  30.4
## 10 33.9
## 11 21.5
## 12 27.3
## 13 30.4
## 14 21.4
sqldf('select mpg ,drat  from mtcars where "vs"= 1')
##     mpg drat
## 1  22.8 3.85
## 2  21.4 3.08
## 3  18.1 2.76
## 4  24.4 3.69
## 5  22.8 3.92
## 6  19.2 3.92
## 7  17.8 3.92
## 8  32.4 4.08
## 9  30.4 4.93
## 10 33.9 4.22
## 11 21.5 3.70
## 12 27.3 4.08
## 13 30.4 3.77
## 14 21.4 4.11