使用RMySQL将列添加到现有的mysql表中

Question

我希望能够将列添加到具有相应类型的现有table 。

这是我尝试的方式：

library("RMySQL")


# Connect to DB
v_db <- dbConnect(MySQL(),
              user="USERNAME", password="PASSWORD",
              dbname="DBNAME", host="localhost")
on.exit(dbDisconnect(v_db))

#Read in my new data (into R)
newcolumn <- read.csv("test.csv")
newcolumn
id   datafornewcolumn
1    4
2    5 
3    8

dbq <- dbSendQuery(v_db, "SELECT * FROM `EXISTINGTABLE`")
dbq <- fetch(dbq, n = -1)
dbq
id  existing columns
1   ...
2   ...
3   ...

dbWriteTable(v_db, "EXISTINGTABLE", merge(dbq, newcolumn, by="id", all.x=TRUE), row.name=FALSE, overwrite=T) 

但是在最后一个语句中，我用新的表覆盖了现有的表，从而丢失了所有相应的变量类型。

然后我尝试了一种解决方法。 将新数据写入SQL中的新table ，然后将其合并到EXISTINGTABLE 。 但是，似乎我无法正确地做到这一点：

dbSendQuery(v_db, "create table workaround (id int not null primary key, 
        newcolumn DECIMAL(3,1))")

#write data into that new empty table called workaround --> works fine
dbWriteTable(v_db, "workaround", neu, row.name=FALSE, append=TRUE)

#something works...
dbSendQuery(v_db, "SELECT * FROM EXISTINGTABLE
     LEFT JOIN workaround ON EXISTINGTABLE.id = workaround.id
     UNION
     SELECT * FROM EXISTINGTABLE
     RIGHT JOIN workaround ON EXISTINGTABLE.id = workaround.id")
<MySQLResult:(29344,26,2)> 

结果应如下所示：

 EXISTINGTABLE
 id  existingcolumns datafornewcolumn
 1   ...             4 
 2   ...             5
 3   ...             8

Answer 1

将列添加到现有表可以完成如下：

library(dbConnect) # *loads the packages Loading required package: RMySQL
                                        Loading required package: DBI
                                        Loading required package: methods
                                        Loading required package: gWidgets*


mydb =dbConnect(MySQL(),user='root',password='newpass',dbname='database_name', host='localhost')

my_table <- dbReadTable(conn=mydb,name='table_name') 
my_table$column_name<- NA # *creates new column named column_name and populates its value NA*
head(my_table) # *shows the data* 

Answer 2

您是否尝试使用带有ALTER TABLE语句的SQL修改表？

rs <- dbSendStatement(v_db, "ALTER TABLE table_name ADD COLUMN [...]")
dbHasCompleted(rs)
dbGetRowsAffected(rs)
dbClearResult(rs)

然后您可以简单地发送和UPDATE语句来添加新值。

首先尝试使用dbExecute()方法...并在R控制台上尝试此操作：

?dbExecute或?dbSendStatement

检查一下： RMySQL dbWriteTable with field.types