R: Translate an expression to sql.

translate_sql {dbplyr}

R Documentation

Translate an expression to sql.

Description

Translate an expression to sql.

Usage

translate_sql(..., con = NULL, vars = character(), vars_group = NULL,
  vars_order = NULL, vars_frame = NULL, window = TRUE)

translate_sql_(dots, con = NULL, vars_group = NULL, vars_order = NULL,
  vars_frame = NULL, window = TRUE)

Arguments

`..., dots`	Expressions to translate. `translate_sql()` automatically quotes them for you. `translate_sql_()` expects a list of already quoted objects.
`con`	An optional database connection to control the details of the translation. The default, `NULL`, generates ANSI SQL.
`vars`	Deprecated. Now call `partial_eval()` directly.
`vars_group, vars_order, vars_frame`	Parameters used in the `OVER` expression of windowed functions.
`window`	Use `FALSE` to suppress generation of the `OVER` statement used for window functions. This is necessary when generating SQL for a grouped summary.

Base translation

The base translator, base_sql, provides custom mappings for ! (to NOT), && and & to AND, || and | to OR, ^ to POWER, %>% to %, ceiling to CEIL, mean to AVG, var to VARIANCE, tolower to LOWER, toupper to UPPER and nchar to LENGTH.

c() and : keep their usual R behaviour so you can easily create vectors that are passed to sql.

All other functions will be preserved as is. R's infix functions (e.g. %like%) will be converted to their SQL equivalents (e.g. LIKE). You can use this to access SQL string concatenation: || is mapped to OR, but %||% is mapped to ||. To suppress this behaviour, and force errors immediately when dplyr doesn't know how to translate a function it encounters, using set the dplyr.strict_sql option to TRUE.

You can also use sql() to insert a raw sql string.

SQLite translation

The SQLite variant currently only adds one additional function: a mapping from sd() to the SQL aggregation function STDEV.

Examples

# Regular maths is translated in a very straightforward way
translate_sql(x + 1)
translate_sql(sin(x) + tan(y))

# Note that all variable names are escaped
translate_sql(like == "x")
# In ANSI SQL: "" quotes variable _names_, '' quotes strings

# Logical operators are converted to their sql equivalents
translate_sql(x < 5 & !(y >= 5))
# xor() doesn't have a direct SQL equivalent
translate_sql(xor(x, y))

# If is translated into case when
translate_sql(if (x > 5) "big" else "small")

# Infix functions are passed onto SQL with % removed
translate_sql(first %like% "Had%")
translate_sql(first %is% NULL)
translate_sql(first %in% c("John", "Roger", "Robert"))

# And be careful if you really want integers
translate_sql(x == 1)
translate_sql(x == 1L)

# If you have an already quoted object, use translate_sql_:
x <- quote(y + 1 / sin(t))
translate_sql_(list(x))

# Windowed translation --------------------------------------------
# Known window functions automatically get OVER()
translate_sql(mpg > mean(mpg))

# Suppress this with window = FALSE
translate_sql(mpg > mean(mpg), window = FALSE)

# vars_group controls partition:
translate_sql(mpg > mean(mpg), vars_group = "cyl")

# and vars_order controls ordering for those functions that need it
translate_sql(cumsum(mpg))
translate_sql(cumsum(mpg), vars_order = "mpg")

[Package dbplyr version 1.1.0 Index]