mysql - 查询变量 RMySQL

Question

我试过这个脚本来使用 RMySQL 在表中选择一个字段:

mydb <- dbConnect(MySQL(), dbname="***", user='***',host='***')
a<-29553
b<-31097
c<-'chr1'
s<-'+'
res<-dbSendQuery(mydb, "SELECT name FROM wgEncodeGencodeBasicV27 WHERE 
chrom=c AND strand=s AND txStart=a AND txEnd=b")

但它返回错误:“‘where 子句’中的未知列‘c’”。为什么？如何更正脚本？

Answer 1

基本上这个想法是您可以在变量的帮助下动态地准备您的查询。这消除了将变量作为参数单独发送的需要。 sprintf 非常适合这个目的。

以 OP 为例。方法应该是:

#Variables to be used in query
a<-29553
b<-31097
c<-'chr1'
s<-'+'

library(RMySQL)

mydb <- dbConnect(MySQL(), dbname="***", user='***',host='***')

#Prepare a query format string with place holders for variables. 
queryFormat <- "SELECT name FROM wgEncodeGencodeBasicV27 
WHERE chrom=`%s` AND strand=`%s` AND txStart=%d AND txEnd=%d"

#Use sprintf to prepare the query
query <- sprintf(queryFormat, c, s, a, b)

res<-dbSendQuery(mydb, query)

#The final query which has been send to Database:
#[1] "SELECT name FROM wgEncodeGencodeBasicV27 
# WHERE chrom=`chr1` AND strand=`+` AND txStart=29553 AND txEnd=31097"