Write values from R to a PostgreSQL table based on Row IDs - r

Question

I have a PostgreSQL table Scores on a local server that looks like this:
ID Score_X Score_Y
1 NA NA
2 NA NA
3 NA NA
4 NA NA
I do a series of calculations in R that produces a dataframe Calc_Scores that looks like this:
ID Score_X Score_Y
1 0.53 0.81
4 0.75 0.95
I would like to write the scores that correspond with each ID from R to the PostgreSQL table such that the final PostgreSQL table should look like this:
ID Score_X Score_Y
1 0.53 0.81
2 NA NA
3 NA NA
4 0.75 0.95
I have a connection to the PostgreSQL table called connection which I setup using the function dbConnect(). The actual tables are quite big. What line/code in R could I use to write these scores to the PostgreSQL table? I have been looking for a similar question but couldn't find anything. I have tried
dbWriteTable(connection, "Scores", value = Calc_Scores, overwrite=T, append = F, row.names = F)
However, the entire table gets overwritten. I want only the scores to be updated.
Thank you.

Answer 1

Creating a temporary table could be an option:
# Create temporary table
dbWriteTable(connection, "ScoresTmp", value = Calc_Scores, overwrite=T, append = F, row.names = F)
# Update main table
dbExecute(connection,"
UPDATE Scores
SET Score_X = ScoresTmp.Score_X,
Score_Y = ScoresTmp.Score_Y
FROM ScoresTmp
WHERE Scores.ID = ScoresTmp.ID
")
# Clean up
dbExecute(connection,"DROP TABLE ScoresTmp")
Note that you should be able to create a real temporary table using the temporary=TRUE option : according to #Sirius comment below, it should work on a PostGreSQL database.
For users of an SQLServer database, this option doesn't work, but they can use the # prefix to create a temporary table.
In the example above, this would be:
dbWriteTable(connection, "#ScoresTmp", value = Calc_Scores, overwrite=T, append = F, row.names = F)

Answer 2

One way of doing this relies on the SQL 'update' and in essence you do
- open a connection to your database
- loop over your changeset and for each row
- form the update statement, i.e. for example via
cmd <- paste('update table set x=', Score_x, ', y=',
Score_y, ' where id=', id)
- submit the cmd via eg `dbSendQuery`
- close the connection
There are examples in RPostgreSQL.