Explain details of a tbl

Description

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

Usage

explain(x, ...)

show_query(x, ...)

Arguments

Value

The first argument, invisibly.

Databases

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.

Examples

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()