SQL

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SQL support in GRASS GIS

GRASS GIS uses SQL for vector attribute management.

Analysing SQL syntax errors/table import or copy problems

Sometimes it happens that db.*, v.db.* or other SQL related commands fail. For example, with

 ERROR:  syntax error at or near "Offset"
 LINE 1: ...eatureDet varchar(254), Measure double precision, Offset dou...
                                                             ^
 WARNING: Unable to create table <hydro_pointEvent>
 WARNING: Copy table failed

How to fix that? Check out for

  • column name used more than one time;
  • column name has reserved SQL word (depends on DB backend, see SQL Reserved Words Checker to quickly find out if a name is reserved)

Formatting

If your data should have values as character with leading zero (000123) but they are lacking (123) then you can run

 alter table TABLE add column NEW_COLUMN text;
 update TABLE set NEW_COLUMN=substr('000000'||OLD_COLUMN, length('000000'||OLD_COLUMN)-5, 6);

Examples

Combining columns for date calculations

An example command that builds a YMD string from a column that contains the Day of Year (DOY) is:

 db.execute sql="UPDATE <DB> SET YMD=date('2015-01-01', +CAST(DOY AS text) || ' days');"