db.execute1grass

Usage

Keywords

database, attribute table, SQL

Overview

db.execute allows the user to execute SQL statements.

Notes

db.execute only executes SQL statements and does not return any data. If you need data returned from the database, use db.select.

If parameters for database connection are already set with db.connect, they are taken as default values and do not need to be specified each time.

If you have a large number of SQL commands to process, it is much faster to place all the SQL statements into a text file and use input file parameter than it is to process each statement individually in a loop. If multiple instruction lines are given, each SQL line must end with a semicolon.

Please see the individual GRASS SQL interface for how to create a new database.

Examples

Create a new table with columns ’cat’ and ’soiltype’:

db.execute sql="CREATE TABLE soils (cat integer, soiltype varchar(10))"

Create a new table using a file with SQL statements

db.execute driver=odbc database=grassdb input=file.sql

Insert new row into attribute table:

db.execute sql="INSERT INTO mysites (id,name,east,north) values (30,’Ala’,1657340,5072301)"

Update attribute entries to new value based on SQL rule:

db.execute sql="UPDATE roads SET travelcost=5 WHERE cat=1"

Update attribute entries to new value based on SQL rule:

db.execute sql="UPDATE dourokukan SET testc=50 WHERE testc is NULL"

Delete selected rows from attribute table:

db.execute sql="DELETE FROM gsod_stationlist WHERE latitude < -91"

Add new column to attribute table:

db.execute sql="ALTER TABLE roads ADD COLUMN length double"

Column type conversion - update new column from existing column (all drivers except for DBF):

# ’z_value’ is varchar and ’z’ is double precision:
echo "UPDATE geodetic_pts SET z = CAST(z_value AS numeric)" | db.execute input=-

Drop column from attribute table:

db.execute sql="ALTER TABLE roads DROP COLUMN length"

Drop table (not supported by all drivers):

db.execute sql="DROP TABLE fmacopy"

Update attribute with multiple SQL instructions in file (e.g., file.sql, instruction line must end with a semicolon):

UPDATE roads SET travelcost=5 WHERE cat=1;
UPDATE roads SET travelcost=2 WHERE cat=2;
db.execute input=file.sql

Join table ’myroads’ to table ’extratab’ based on common ’cat’ column values (not supported by DBF driver):

db.execute sql="UPDATE extratab SET names=(SELECT label FROM myroads WHERE extratab.cat=myroads.cat)"

Source code

Available at: db.execute source code (history)

Accessed: Monday Feb 24 17:50:22 2025

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