trusty (1) grass-dbf.1grass.gz

NAME

       grass-dbf - DBF driver

       DBF driver DBF driver in GRASS

Defining the DBF driver

       The DBF driver is the default driver, in theory no user interaction is required. However, if the settings
       should be set back from a different to the DBF driver, the following step is required:
       # keep single quotes:
       db.connect driver=dbf database='$GISDBASE/$LOCATION_NAME/$MAPSET/dbf/'
       db.connect -p
        The dbf/ subdirectory in the mapset must exist or must be created by the user.

Creating a DBF table

       Usually DBF tables are created by GRASS when generating a vector map with attributes (and  using  DBF  as
       default attribute driver).

       If  a  DBF  table  has  to be created manually, db.execute can be used or a spreadsheet application. Also
       db.copy is sometimes useful as well as db.in.ogr to import external tables.

Supported SQL commands by DBF driver

         ALTER TABLE table ADD [COLUMN] columndef
         ALTER TABLE table DROP COLUMN colname
         CREATE TABLE table ( columndefs )
         DROP TABLE table
         SELECT columns FROM table
         SELECT columns FROM table WHERE condition
         SELECT columns FROM table ORDER BY column
         DELETE FROM table
         DELETE FROM table WHERE condition
         INSERT INTO table VALUES (value1[,value2,...])
         INSERT INTO table ( column1[,column2,...] ) VALUES (value1[,value2,...])
         UPDATE table SET assignment1[,assignment2,...]
         UPDATE table SET assignment1[,assignment2,...] WHERE condition

Operators available in conditions

         "="  : equal
         "<"  : smaller than
         "<=" : smaller/equal than
         ">"  : larger than
         ">=" : larger/equal than
         "<>" : not equal
         "~"  : Substring matching  (non-standard SQL)
         "%"  : Substring matching  (limited functionality)

       Arithmetic expressions using constants and field values are allowed in condition clauses and in  the  RHS
       of assignments.
       Usual precedence rules and bracketing (using '(' and ')') are supported.
       Type conversion is performed if necessary (experimental).

       Conditions  allow  boolean  expressions  using  the  AND, OR and NOT operators, with the usual precedence
       rules.

       NULLs can be tested by 'colname IS NULL' in conditions. The negation is ’colname NOT NULL'.

       Sorting: Empty fields in a character column are sorted to the end.

LIMITATIONS OF THE DBF DRIVER

       The DBF driver supports only a few SQL statements since the DBF tables  are  intended  for  simple  table
       storage.  DBF  column  names  are  limited  to  10 characters (as defined in the DBF specifications). For
       example,

                      aggregate functions (sum, count, min, max,...) are not supported in SELECT clauses;

                      mathematic functions (sin, cos, exp, log,...) are not supported in expressions;

                      SQL query with IN are not supported.

ERROR MESSAGES

       An error message such as:
       DBMI-DBF driver error:
       SQL parser error: syntax error, unexpected NAME processing 'IN'..
        indicates that an unsupported SQL statement (here, 'IN') was used. The only solution is  to  switch  the
       DBMI backend to a real SQL engine (SQLite, PostgreSQL, MySQL etc.). See SQL support in GRASS GIS.

       An error message such as:
       DBMI-DBF driver error:
       SQL parser error: syntax error, unexpected DESC, expecting NAME processing 'DESC'
        indicates that a column name corresponds to a reserved SQL word (here: 'DESC').  A different column name
       should be used. If this happens during import with v.in.ogr, the cnames parameter can be used  to  assign
       different column names on the fly.

SEE ALSO

        db.connect, SQL support in GRASS GIS
       DBF Specifications (Shapelib)

       Last changed: $Date: 2012-09-07 01:20:29 -0700 (Fri, 07 Sep 2012) $
       Main index - database index - full index