Insert R list into RPostgreSQL query - r

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.

Related

Passing a vector of characters into another string in R

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

Join a data frame (or other R object) to a table in a read-only Postgresql database?

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 = ", ")
)

convert variable to text or string in R

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'"

RMySQL retrieving data from database table basing on an if statement

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 )
}

Using variable in "IN" function of SQL query in R

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 = ","), ")"))

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