I am trying to retrieve data from a database table based on a given condition:
I want to select all from a table, and during the while loop I put a condition like to return only what I want the way it is done in PHP
mytable <- dbSendQuery(con, "select date from member")
while(!dbHasCompleted(mytable)){
if(name = 'myname'){
new_date <- dbFetch(mytable, n=-1)
print(mytable)
}
}
How do I deal with the if statements to operate well?
I later found out the solution like this
mytable <- dbSendQuery(con, "select * from member")
while(!dbHasCompleted(mytable)){
new_date <- dbFetch(mytable, name = 'john', n=-1)
print(new_date )
}
Related
I have read-only access to a Postgres database. I can not write to the database.
Q. Is there a way to construct and run a SQL query where I join a data frame (or other R object) to a table in a read-only Postgres database?
This is for accessing data from WRDS, https://wrds-www.wharton.upenn.edu/
Here's an attempt at pseudocode
#establish a connection to a database
con <- dbConnect( Postgres(),
host = 'host.org',
port = 1234,
dbname = 'db_name',
sslmode = 'require',
user = 'username', password = 'password')
#create an R dataframe (or other object)
df <- data.frame( customer_id = c('a123', 'a-345', 'b0') )
#write a sql query we will run
sql_query <- "
SELECT t.customer_id, t.* FROM df t
LEFT JOIN table_name df
on t.customer_id = df.customer_id
"
my_query_results <- dbSendQuery(con, sql_query)
temp <- dbFetch(res, n = 1)
dbClearResult(res)
my_query_results
Note and edit: The example query I provided is intentionally super simple for example purposes.
In my actual queries, there might be 3 or more columns I want to join on, and millions of rows I want to join on.
Use the copy_inline function from the dbplyr package, which was added following an issue filed on this topic. See also the question here.
An example of its use is found here.
If your join is on a single condition, it can be rewritten using an in clause:
In SQL:
SELECT customer_id
FROM table_name
WHERE customer_id in ('a123', 'a-345', 'b0')
Programmatically from R:
sql_query = sprintf(
"SELECT customer_id
FROM table_name
WHERE customer_id in (%s)",
paste(sQuote(df$customer_id, q = FALSE), collapse = ", ")
)
I'm running a postgreSQL query based on an automated list of ID's stored in an R list. I'm trying to determine how to include that R list in my query so I don't have to hard-code the ID's each time I run my query.
For example, I have a script that produces the list
id <- c("001","002","003")
and my query looks something like this:
SELECT *
FROM my_query
WHERE my_query.id_col IN ('001', '002', '003')
which I run using Rpostgres:
library(Rpostgres)
snappConnection <- DBI::dbConnect(RPostgres::Postgres(),
host = "host",
dbname = "dbname",
user = "user",
password = "pword",
port = 0000)
core.data <- dbGetQuery(conn = snappConnection,statement = SELECT * FROM my_query WHERE my_query.id_col IN ('001', '002', '003'))
Is there a way to reference my "id" list from R in my query so that when "id" updates to new values, the query also updates to those new values?
glue_sql from glue package should work:
query <- glue::glue_sql("
SELECT *
FROM my_query
WHERE my_query.id_col IN ({id*})
", .con = snappConnection)
core.data <- dbGetQuery(conn = snappConnection, statement = query)
#dave-edison's answer solved my problem. Concurrent to trying his, I got this to work.
I saved the query below as "my_query.sql"
SELECT *
FROM my_query
WHERE my_query.id_col IN ('string_to_replace')
then created a string and used gsub on the string.
library(tidyverse)
temp.script <- read_file("my_query.sql")
core.data.script <- gsub('string_to_replace',paste0(id,collapse = "', '"),temp.script)
From there I just ran my RPostgres script like above.
I am trying to convert a "datetime" variable to "datetime2" format.
# Load libraries
library(DBI)
library(tidyverse)
# Create dataframe
df <- data.frame("myid" = stringi::stri_rand_strings(5, 5),
"mydate" = c(Sys.time(), Sys.time()-1, Sys.time()-2, Sys.time()-3, Sys.time()-4) )
# Create SQL table sschema.ttable
DBI::dbWriteTable(conn = connection,
name = DBI::Id(schema = "sschema", table = "ttable"),
value = df,
overwrite = TRUE,
append = FALSE)
# Query for variable type in the SQL table
query <- paste0("exec sp_columns ", "ttable")
query <- DBI::dbSendQuery(connection, query)
res <- NULL
res <- DBI::dbFetch(query)
DBI::dbClearResult(query)
view(res)
# Alter mydate to datetime2
query <- DBI::dbSendStatement(conn = connection,
statement = paste0("ALTER TABLE sschema.ttable ALTER COLUMN mydate datetime2"))
DBI::dbFetch(query)
DBI::dbClearResult(query)
but this leads to the error
Error: nanodbc/nanodbc.cpp:1617: 00000: [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]The UPDATE permission was denied on the object 'ttable', database 'dbo', schema 'sschema'.
'ALTER TABLE sschema.ttablename ALTER COLUMN mydate datetime2'
However, converting another VARCHAR(10) variable in the same table to VARCHAR(100) works fine. Any idea what is the problem? How to get this working?
I am working with Microsoft SQL Azure version 12, by operating on an RStudio-server and the DBI library.
To change the data type of a column you must have both the ALTER permission and UPDATE permission on the table.
From the docs:
Adding a column that updates the rows of the table requires UPDATE permission on the table.
ALTER TABLE - permissions
This goes for ALTERing an existing column too, as you can verify like this:
use tempdb
go
revert
go
if exists(select * from sys.database_principals where name = 'fred')
drop user fred
go
drop table if exists tablename
go
create user fred without login
create table tablename(id int, variablename varchar(20))
go
grant select on tablename to fred
--grant update on tablename to fred --uncomment to clear error
grant alter on schema::dbo to fred
execute as user='fred'
ALTER TABLE dbo.tablename ALTER COLUMN variablename datetime2
revert
I created a connection:
library(RODBC)
pswd <- readline("Input Password: ")
channel<-odbcConnect (dsn="dsn",uid="uid",pwd=pswd,believeNRows=FALSE)
And I am able to get a list of tables
tables <- sqlTables(channel, schema="SYSADM")
But when I try to query one of the tables
query <- "select * from SYSADM.TABLE1"
dataframe <- sqlQuery(channel,query)
I get:
"[RODBC] ERROR: Could not SQLExecDirect 'SELECT * FROM \"TABLE1\"'"
I do have access to this table and am able to query it using Toad.
What could be the issue?
Kindly make a change as follows and then try below queries:
tables <- sqlTables(channel, schema='SYSADM')
Queries:
dataframe <- sqlQuery(channel,"select * from SYSADM.TABLE1")
Or
query <- paste("select * from SYSADM.TABLE1")
dataframe <- sqlQuery(channel,"select * from SYSADM.TABLE1")
Hope it helps!
I am having a variable x which contains 20000 IDs. I want to write a sql query like,
select * from tablename where ID in x;
I am trying to implement this in R where I can get the values only for IDs in x variable. The following is my try,
dbSendQuery(mydb, "select * from tablename where ID in ('$x') ")
I am not getting any error while trying this. But it is returning 0 values.
Next tried using
sprintf("select * from tablename where ID in %s",x)
But this is creating 20000 individual queries which could prove costly in DB.
Can anybody suggest me a way to write a command, which would loop through IDs in x and save to a Dataframe in R in a single query?
You need to have the codes in the actual string. Here is how I would do it with gsub
x <- LETTERS[1:3]
sql <- "select * from tablename where ID in X_ID_CODES "
x_codes <- paste0("('", paste(x, collapse="','"), "')")
sql <- gsub("X_ID_CODES", x_codes, sql)
# see new output
cat(sql)
select * from tablename where ID in ('A','B','C')
# then submit the query
#dbSendQuery(mydb, sql)
How about pasting it:
dbSendQuery(mydb, paste("select * from tablename where ID in (", paste(x, collapse = ","), ")"))