I would like to know how to pass a vector of text into a string within R.
I have a list of emails stored as a character vector:
all.emails <-
list(
c('email_1#emailaddress_1.com',
'email_2#emailaddress_2.com',
'email_3#emailaddress_3.com',
'email_r#emailaddress_n.com'
)
)
Also within R, I have some SQL code stored as a string that I will pass to our database via a database connection in R. To do this, I created a string that is the query written in SQL but I want to pass the emails above into the string below so I can query the database only for those emails.
The SQL query will look something like this:
sql <-
"
1> SELECT column_1, column_2,..., column_n
2> FROM name.of.table
3> WHERE toaddress = '[this is where to pass the email list above into]'.
"
It is line 3 where I need to pass my email list into.
Any help will be appreciated.
You can create the sql statement as follows:
sql = paste0(
"SELECT column_1, column_2,..., column_n ",
"FROM name.of.table ",
"WHERE toaddress IN ('",
paste0(unlist(all.emails),collapse="','"),
"')"
)
Output:
"SELECT column_1, column_2,..., column_n FROM name.of.table WHERE toaddress IN ('email_1#emailaddress_1.com','email_2#emailaddress_2.com','email_3#emailaddress_3.com','email_r#emailaddress_n.com')"
If you are going to generate a lot of SQL, I recommend that you look into glue_sql(), because it is especially designed for this use case and has a lot of nice features:
library(glue)
## set up example db:
con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
DBI::dbWriteTable(con, "chickwts", chickwts)
tbl <- "chickwts"
feed <- list("soybean", "sunflower")
feed <- glue_sql_collapse(single_quote(feed), sep = ", ")
glue_sql("
SELECT * FROM {`tbl`}
WHERE feed IN ({feed})
", .con = con)
#> <SQL> SELECT * FROM `chickwts`
#> WHERE feed IN ('soybean', 'sunflower')
Created on 2022-10-21 with reprex v2.0.2
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 read data from excel file to connect and use in postgreSQL. I could connect to database and need to query using the variables from excel file. This part is working fine.
I declara a variable from excel file say "school" which I need to use dynamically to query in database. below is my query
sid <- '500'
my_school <- RPostgreSQL::dbGetQuery(conn = con, statement = "SELECT * from school where school_id = sid ")
it works if I use "500" instead of sid but I need to use a dynamic variable.
the error I get is :
Error: Failed to prepare query: ERROR: column "sid" does not exist
LINE 1: SELECT * from school where school_id = sid
^
HINT: Perhaps you meant to reference the column "school.db_sid".
>
Could anyone look at this? Thanks.
Use sprintf:
sprintf("SELECT * from school where school_id = %s", sid)
#[1] "SELECT * from school where school_id = 500"
Add quotation marks if appropriate:
sprintf("SELECT * from school where school_id = '%s'", sid)
#[1] "SELECT * from school where school_id = '500'"
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 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 = ","), ")"))
Having trouble understanding how to pass a dataframe's column value to the query? The query works fine if I pass the value directly.
The values are stored in df$number. The tables names are changed for sharing purposes:
dataframe <- sqlQuery(connection, "
+ SELECT
+ dimension1,
+ FROM
+ table1,
+ WHERE
+ dimension1 = df$number ")
I get the error [1] "42S22 904 [Oracle][ODBC][Ora]ORA-00904: \"df$number\": invalid identifier\n"
The gsubfn package can perform quasi-perl-style string interpolation. Preface any function with fn$ to turn it on for that function's arguments:
library(gsubfn)
num <- 3
dataframe <- fn$sqlQuery(connection,
"SELECT dimension1 FROM table1 WHERE dimension1 = $num ")
Alternately use paste or sprintf to construct the string:
sql <- paste("SELECT dimension1 FROM table1 WHERE dimension1 =", num)
sqlQuery(connection, sql)
or
sql <- sprintf("SELECT dimension1 FROM table1 WHERE dimension1 = %d", num)
sqlQuery(connection, sql)
dataframe <- sqlQuery(connection, paste("
+ SELECT
+ dimension1,
+ FROM
+ table1,
+ WHERE
+ dimension1 =", df$number))
The SQL statement is a string, so it cannot access your dataframe's value. To construct a string which uses the value use:
sql.base<-"SELECT dimension1 FROM table1 WHERE dimension1 = "
sql.completed<-paste0(sql.base,df$number)
sqlQuery(connection, sql.completed)
If you're looking to do a parameterized SQL query i.e. you have a number of rows in df, you can either collapse the field values with a comma seperator and put them in side brackets within a SQL IN query. Alternatively you can use the package RODBCext which will allow to do it like
sqlExecute(connection, "SELECT dimension1 FROM table1 WHERE dimension1 = ?", df$number, fetch = TRUE)
For more info on RODBCext and this type of SQL, check out their vignette