glue: glue_sql – R documentation

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glue_sql

Interpolate strings with SQL escaping

Description

SQL databases often have custom quotation syntax for identifiers and strings which make writing SQL queries error prone and cumbersome to do. glue_sql() and glue_data_sql() are analogs to glue() and glue_data() which handle the SQL quoting.

Usage

glue_sql(..., .con, .envir = parent.frame(), .na = DBI::SQL("NULL"))

glue_data_sql(.x, ..., .con, .envir = parent.frame(), .na = DBI::SQL("NULL"))

Arguments

`...`	[`expressions`] Unnamed arguments are taken to be expressions string(s) to format. Multiple inputs are concatenated together before formatting. Named arguments are taken to be temporary variables available for substitution.
`.con`	[`DBIConnection`]:A DBI connection object obtained from `DBI::dbConnect()`.
`.envir`	[`environment`: `parent.frame()`] Environment to evaluate each expression in. Expressions are evaluated from left to right. If `.x` is an environment, the expressions are evaluated in that environment and `.envir` is ignored. If `NULL` is passed it is equivalent to `emptyenv()`.
`.na`	[`character(1)`: ‘NA’] Value to replace NA values with. If `NULL` missing values are propagated, that is an `NA` result will cause `NA` output. Otherwise the value is replaced by the value of `.na`.
`.x`	[`listish`] An environment, list or data frame used to lookup values.

Details

They automatically quote character results, quote identifiers if the glue expression is surrounded by backticks '`' and do not quote non-characters such as numbers. If numeric data is stored in a character column (which should be quoted) pass the data to glue_sql() as a character.

Returning the result with DBI::SQL() will suppress quoting if desired for a given value.

Note parameterized queries are generally the safest and most efficient way to pass user defined values in a query, however not every database driver supports them.

If you place a * at the end of a glue expression the values will be collapsed with commas. This is useful for the SQL IN Operator for instance.

Value

A DBI::SQL() object with the given query.

Examples

con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
iris2 <- iris
colnames(iris2) <- gsub("[.]", "_", tolower(colnames(iris)))
DBI::dbWriteTable(con, "iris", iris2)
var <- "sepal_width"
tbl <- "iris"
num <- 2
val <- "setosa"
glue_sql("
  SELECT {`var`}
  FROM {`tbl`}
  WHERE {`tbl`}.sepal_length > {num}
    AND {`tbl`}.species = {val}
  ", .con = con)

# If sepal_length is store on the database as a character explicitly convert
# the data to character to quote appropriately.
glue_sql("
  SELECT {`var`}
  FROM {`tbl`}
  WHERE {`tbl`}.sepal_length > {as.character(num)}
    AND {`tbl`}.species = {val}
  ", .con = con)


# `glue_sql()` can be used in conjuction with parameterized queries using
# `DBI::dbBind()` to provide protection for SQL Injection attacks
 sql <- glue_sql("
    SELECT {`var`}
    FROM {`tbl`}
    WHERE {`tbl`}.sepal_length > ?
  ", .con = con)
query <- DBI::dbSendQuery(con, sql)
DBI::dbBind(query, list(num))
DBI::dbFetch(query, n = 4)
DBI::dbClearResult(query)

# `glue_sql()` can be used to build up more complex queries with
# interchangeable sub queries. It returns `DBI::SQL()` objects which are
# properly protected from quoting.
sub_query <- glue_sql("
  SELECT *
  FROM {`tbl`}
  ", .con = con)

glue_sql("
  SELECT s.{`var`}
  FROM ({sub_query}) AS s
  ", .con = con)

# If you want to input multiple values for use in SQL IN statements put `*`
# at the end of the value and the values will be collapsed and quoted appropriately.
glue_sql("SELECT * FROM {`tbl`} WHERE sepal_length IN ({vals*})",
  vals = 1, .con = con)

glue_sql("SELECT * FROM {`tbl`} WHERE sepal_length IN ({vals*})",
  vals = 1:5, .con = con)

glue_sql("SELECT * FROM {`tbl`} WHERE species IN ({vals*})",
  vals = "setosa", .con = con)

glue_sql("SELECT * FROM {`tbl`} WHERE species IN ({vals*})",
  vals = c("setosa", "versicolor"), .con = con)

# If you need to reference a variables from multiple tables use `DBI::Id()`.
# Here we create a new table of nicknames, join the two tables together and
# select columns from both tables. Using `DBI::Id()` and the special
# `glue_sql()` syntax ensures all the table and column identifiers are quoted
# appropriately.

iris_db <- "iris"
nicknames_db <- "nicknames"

nicknames <- data.frame(
  species = c("setosa", "versicolor", "virginica"),
  nickname = c("Beachhead Iris", "Harlequin Blueflag", "Virginia Iris"),
  stringsAsFactors = FALSE
)

DBI::dbWriteTable(con, nicknames_db, nicknames)

cols <- list(
  DBI::Id(table = iris_db, column = "sepal_length"),
  DBI::Id(table = iris_db, column = "sepal_width"),
  DBI::Id(table = nicknames_db, column = "nickname")
)

iris_species <- DBI::Id(table = iris_db, column = "species")
nicknames_species <- DBI::Id(table = nicknames_db, column = "species")

query <- glue_sql("
  SELECT {`cols`*}
  FROM {`iris_db`}
  JOIN {`nicknames_db`}
  ON {`iris_species`}={`nicknames_species`}",
  .con = con
)
query

DBI::dbGetQuery(con, query, n = 5)

DBI::dbDisconnect(con)

glue

Interpreted String Literals

v1.4.2

MIT + file LICENSE

Authors

Jim Hester [aut, cre]

Initial release