explain: Explain details of a tbl

View source: R/explain.r

explainR Documentation

Explain details of a tbl


This is a generic function which gives more details about an object than print(), and is more focused on human readable output than str().


explain(x, ...)

show_query(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.


lahman_s <- dbplyr::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()

dplyr documentation built on Sept. 1, 2022, 5:06 p.m.