How to extract features from a vector layer?

Question

I have a vector file containing the river lines of an area. I want to extract a specific water line from the vector. I used: v.db.select but it only displayed:

   cat|F_CODE_DES|HYC_DESCRI|NAM|ISO|NAME_0
    1|River/Stream|Perennial/Permanent|UNK|PHL|Philippines
    2|River/Stream|Perennial/Permanent|UNK|PHL|Philippines
    3|River/Stream|Perennial/Permanent|UNK|PHL|Philippines
...

then i used v.extract to select a specific area and it displayed this error:

v.extract input=vector_waterLines@PERMANENT output=vector_1 where=1             
DBMI-DBF driver error:
ERROR: Unable select records from table <vector_waterLines>

Answer 1

The where switch should be an SQL statement. From the GRASS manual:

where=sql_query WHERE conditions of SQL statement without 'where' keyword Example: income < 1000 and inhab >= 10000

For example, if you want to extract only perennial streams:

v.extract input=vector_waterLines@PERMANENT output=vector_1 where="HYC_DESCRI = 'Perennial/Permanent'"