Explain details of a tbl
explain(x, ...) show_query(x, ...)
x |
An object to explain |
... |
Other parameters possibly used by generic |
The first argument, invisibly.
Explaining a tbl_sql will run the SQL EXPLAIN command which
will describe the query plan. This requires a little bit of knowledge about
how EXPLAIN works for your database, but is very useful for
diagnosing performance problems.
if (require("dbplyr")) {
lahman_s <- lahman_sqlite()
batting <- tbl(lahman_s, "Batting")
batting %>% show_query()
batting %>% explain()
# The batting database has indices on all ID variables:
# SQLite automatically picks the most restrictive index
batting %>% filter(lgID == "NL" & yearID == 2000L) %>% explain()
# OR's will use multiple indexes
batting %>% filter(lgID == "NL" | yearID == 2000) %>% explain()
# Joins will use indexes in both tables
teams <- tbl(lahman_s, "Teams")
batting %>% left_join(teams, c("yearID", "teamID")) %>% explain()
}Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.