The dbSendQuery() method only submits and synchronously executes the SQL query to the database engine. It does not extract any records --- for that you need to use the dbFetch() method, and then you must call dbClearResult() when you finish fetching the records you need. For interactive use, you should almost always prefer dbGetQuery().

Methods in other packages

  • RSQLite::dbSendQuery("SQLiteConnection", "character")

dbSendQuery(conn, statement, ...)

Arguments

conn

A DBIConnection object, as returned by dbConnect().

statement

a character string containing SQL.

...

Other parameters passed on to methods.

Value

dbSendQuery() returns an S4 object that inherits from DBIResult. The result set can be used with dbFetch() to extract records. Once you have finished using a result, make sure to clear it with dbClearResult(). An error is raised when issuing a query over a closed or invalid connection, or if the query is not a non-NA string. An error is also raised if the syntax of the query is invalid and all query parameters are given (by passing the params argument) or the immediate argument is set to TRUE.

Details

This method is for SELECT queries only. Some backends may support data manipulation queries through this method for compatibility reasons. However, callers are strongly encouraged to use dbSendStatement() for data manipulation statements.

The query is submitted to the database server and the DBMS executes it, possibly generating vast amounts of data. Where these data live is driver-specific: some drivers may choose to leave the output on the server and transfer them piecemeal to R, others may transfer all the data to the client -- but not necessarily to the memory that R manages. See individual drivers' dbSendQuery() documentation for details.

Additional arguments

The following arguments are not part of the dbSendQuery() generic (to improve compatibility across backends) but are part of the DBI specification:

  • params (default: NULL)

  • immediate (default: NULL)

They must be provided as named arguments. See the "Specification" sections for details on their usage.

Specification

No warnings occur under normal conditions. When done, the DBIResult object must be cleared with a call to dbClearResult(). Failure to clear the result set leads to a warning when the connection is closed.

If the backend supports only one open result set per connection, issuing a second query invalidates an already open result set and raises a warning. The newly opened result set is valid and must be cleared with dbClearResult().

The param argument allows passing query parameters, see dbBind() for details.

Specification for the immediate argument

The immediate argument supports distinguishing between "direct" and "prepared" APIs offered by many database drivers. Passing immediate = TRUE leads to immediate execution of the query or statement, via the "direct" API (if supported by the driver). The default NULL means that the backend should choose whatever API makes the most sense for the database, and (if relevant) tries the other API if the first attempt fails. A successful second attempt should result in a message that suggests passing the correct immediate argument. Examples for possible behaviors:

  1. DBI backend defaults to immediate = TRUE internally

    1. A query without parameters is passed: query is executed

    2. A query with parameters is passed:

      1. params not given: rejected immediately by the database because of a syntax error in the query, the backend tries immediate = FALSE (and gives a message)

      2. params given: query is executed using immediate = FALSE

  2. DBI backend defaults to immediate = FALSE internally

    1. A query without parameters is passed:

      1. simple query: query is executed

      2. "special" query (such as setting a config options): fails, the backend tries immediate = TRUE (and gives a message)

    2. A query with parameters is passed:

      1. params not given: waiting for parameters via dbBind()

      2. params given: query is executed

See also

Examples

con <- dbConnect(RSQLite::SQLite(), ":memory:") dbWriteTable(con, "mtcars", mtcars) rs <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4") dbFetch(rs)
#> mpg cyl disp hp drat wt qsec vs am gear carb #> 1 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1 #> 2 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 #> 3 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2 #> 4 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1 #> 5 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2 #> 6 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1 #> 7 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1 #> 8 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1 #> 9 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2 #> 10 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2 #> 11 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
dbClearResult(rs) # Pass one set of values with the param argument: rs <- dbSendQuery( con, "SELECT * FROM mtcars WHERE cyl = ?", params = list(4L) ) dbFetch(rs)
#> mpg cyl disp hp drat wt qsec vs am gear carb #> 1 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1 #> 2 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 #> 3 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2 #> 4 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1 #> 5 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2 #> 6 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1 #> 7 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1 #> 8 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1 #> 9 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2 #> 10 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2 #> 11 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
dbClearResult(rs) # Pass multiple sets of values with dbBind(): rs <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = ?") dbBind(rs, list(6L)) dbFetch(rs)
#> mpg cyl disp hp drat wt qsec vs am gear carb #> 1 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4 #> 2 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4 #> 3 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1 #> 4 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1 #> 5 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4 #> 6 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4 #> 7 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
dbBind(rs, list(8L)) dbFetch(rs)
#> mpg cyl disp hp drat wt qsec vs am gear carb #> 1 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2 #> 2 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4 #> 3 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3 #> 4 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3 #> 5 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3 #> 6 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4 #> 7 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4 #> 8 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4 #> 9 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2 #> 10 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2 #> 11 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4 #> 12 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2 #> 13 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4 #> 14 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8