odbcPreviewObject: Optimize SELECT against rowLimit #525
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
hadley
approved these changes
Jan 3, 2023
| @@ -238,7 +238,39 @@ odbcPreviewObject.OdbcConnection <- function(connection, rowLimit, table = NULL, | |||
| name <- paste(dbQuoteIdentifier(connection, catalog), name, sep = ".") | |||
| } | |||
|
|
|||
| dbGetQuery(connection, paste("SELECT * FROM", name), n = rowLimit) | |||
| dbGetQuery(connection, odbcPreviewQuery(connection, rowLimit, name ), | |||
There was a problem hiding this comment.
Argument alignment; again http://github.com/lionel-/codegrip is likely the easiest way to see what we want.
|
|
||
| #' Common top-N syntax ( MYSQL, PSQL, DB2, SNOWFLAKE, etc ) | ||
| #' @rdname odbcPreviewQuery | ||
| odbcPreviewQuery.OdbcConnection <- function(connection, rowLimit, name) { |
There was a problem hiding this comment.
Probably worth a couple of tests?
hadley
reviewed
Jan 5, 2023
tests/testthat/test-MySQL.R
Outdated
| @@ -78,9 +78,10 @@ test_that("MySQL", { | |||
| con <- DBItest:::connect(DBItest:::get_default_context()) | |||
| dbWriteTable(con, tblName, data.frame(a = 1:10L)) | |||
| on.exit(dbRemoveTable(con, tblName)) | |||
| # There should be no "Pending rows" warning | |||
| expect_warning({ | |||
There was a problem hiding this comment.
You can use expect_no_warning() now, for a bit more clarity.
detule
force-pushed
the
feature/preview_query
branch
from
bcc1966 to
fa3e3ed
Compare
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This closes #502
When previewing large tables, optimize the
SELECT *query since we are only interested in a limited number of rows.Testing locally against SQL Server with tables as larges as 70K rows shows limited benefits. However, when testing against a Snowflake instance with > 1B rows tables, benefit is very tangible.
Note: Current default for the query of the preview format is
SELECT * FROM <table> LIMIT N, with exceptions for SQL Server, and Oracle. Tested theLIMIT Nsyntax successfully against MYSQL, PSQL, DB2, SNOWFLAKE. If there are users of other more esoteric back-ends that do not support theLIMIT Nsuffix, we can add S3 methods for them.Alternative would have been to leave the default preview query un-optimized as
SELECT * FROM <table>, and write S3 methods for all of the above that route to theLIMIT Nimplementation.I have a small bias for the way it is written in this commit ( assume
LIMIT Nworks for other back-ends and address as needed ), but can go either way.Thanks