GRASS-DBF driver

# DBF driver in GRASS

## Creating a DBF table

Usually DBF tables are created by GRASS when generating a vector map with attribute (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.

## Supported SQL commands by DBF driver

      ALTER TABLE table ADD [COLUMN] columndef
      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

## Operators available in conditions

      "="  : equal
      "<"  : smaller than
      "<=" : smaller/equal than
      ">"  : larger than
      ">=" : larger/equal than
      "<>" : not equal
      "~"  : Substring matching

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).

Aggregate functions (sum, count, min, max,...) are NOT currently supported in SELECT clauses.

Mathematic functions (sin, cos, exp, log,...) are NOT currently supported in expressions.

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'.

## SEE ALSO

SQL support in GRASS GIS

Last changed: $Date: 2006/08/24 19:11:36 $

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