dbSendQuery: Execute a query on a given database connection

Description Usage Arguments Details Value Additional arguments Specification See Also Examples

Description

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().

\Sexpr[results=rd,stage=render]{DBI:::methods_as_rd("dbSendQuery")}

Usage

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dbSendQuery(conn, statement, ...)

Arguments

conn

A DBIConnection object, as returned by dbConnect().

statement

a character string containing SQL.

...

Other parameters passed on to methods.

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.

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, if the syntax of the query is invalid, or if the query is not a non-NA string.

Additional arguments

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

It must be provided as named arguments. See the "Specification" sections for details on its 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.

See Also

For updates: dbSendStatement() and dbExecute().

Other DBIConnection generics: DBIConnection-class, dbAppendTable, dbCreateTable, dbDataType, dbDisconnect, dbExecute, dbExistsTable, dbGetException, dbGetInfo, dbGetQuery, dbIsReadOnly, dbIsValid, dbListFields, dbListObjects, dbListResults, dbListTables, dbReadTable, dbRemoveTable, dbSendStatement, dbWriteTable

Examples

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con <- dbConnect(RSQLite::SQLite(), ":memory:")

dbWriteTable(con, "mtcars", mtcars)
rs <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4")
dbFetch(rs)
dbClearResult(rs)

# Pass one set of values with the param argument:
rs <- dbSendQuery(
  con,
  "SELECT * FROM mtcars WHERE cyl = ?",
  param = list(4L)
)
dbFetch(rs)
dbClearResult(rs)

# Pass multiple sets of values with dbBind():
rs <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = ?")
dbBind(rs, list(6L))
dbFetch(rs)
dbBind(rs, list(8L))
dbFetch(rs)
dbClearResult(rs)

dbDisconnect(con)

Example output

    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
    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
   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
    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

DBI documentation built on May 2, 2018, 5:04 p.m.