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<h1>DBF driver in GRASS</h1>
<H2>Defining the DBF driver</H2>
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:
<div class="code"><pre>
# keep single quotes:
db.connect driver=dbf database='$GISDBASE/$LOCATION_NAME/$MAPSET/dbf/'
db.connect -p
</pre></div>
The dbf/ subdirectory in the mapset must exist or must be created by the user.
<H2>Creating a DBF table</H2>
Usually DBF tables are created by GRASS when generating a vector map
with attributes (and using DBF as default attribute driver).
<p>
If a DBF table has to be created manually, <a href="db.execute.html">db.execute</a>
can be used or a spreadsheet application. Also <a href="db.copy.html">db.copy</a>
is sometimes useful as well as <a href="db.in.ogr.html">db.in.ogr</a> to import external
tables.
<H2>Supported SQL commands by DBF driver</H2>
<div class="code"><pre>
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
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
</pre></div>
<H2>Operators available in conditions</H2>
<div class="code"><pre>
"=" : equal
"<" : smaller than
"<=" : smaller/equal than
">" : larger than
">=" : larger/equal than
"<>" : not equal
"~" : Substring matching (non-standard SQL)
"%" : Substring matching (limited functionality)
</pre></div>
<p> 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). </p>
<p> Aggregate functions (sum, count, min, max,...) are NOT currently supported
in SELECT clauses. </p>
<p> Mathematic functions (sin, cos, exp, log,...) are NOT currently supported
in expressions. </p>
<p> Conditions allow boolean expressions using the AND, OR and NOT operators,
with the usual precedence rules. </p>
<p> NULLs can be tested by 'colname IS NULL' in conditions. The negation is 'colname NOT NULL'.</p>
<h2>ERROR MESSAGES</h2>
An error message such as:
<div class="code"><pre>
DBMI-DBF driver error:
SQL parser error: syntax error, unexpected DESC, expecting NAME processing 'DESC'
</pre></div>
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
<em>v.in.ogr</em>, the <em>cnames</em> parameter can be used to assign different
column names on the fly.
<h2>SEE ALSO</h2>
<em>
<a HREF="db.connect.html">db.connect</a>,
<a HREF="sql.html">SQL support in GRASS GIS</a><br>
<a href="http://shapelib.maptools.org/dbf_api.html">DBF Specifications</a> (Shapelib)
</em>
<p><i>Last changed: $Date: 2007-07-18 16:10:27 +0200 (Wed, 18 Jul 2007) $</i>
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