sql query with WHERE

i am开发者_Go百科 trying to implement a detabase query using WHERE, and really just wondering how to implement it? the code i have here gives me an error ;/ thnánk you!

        public Cursor fetchAllCatagoryForSign(String sign) {
        String signSelect="";
        if(sign!=null){
            signSelect=" WHERE " + CATAGORY_SIGN + "=" + sign;
        }
        return mDb.rawQuery("SELECT " + CATAGORY_ID + "," +
                " " + CATAGORY_NAME +  "," +
                " " + CATAGORY_SIGN + " FROM "
                + CATAGORY_TABLE + signSelect + 
                " ORDER BY " + CATAGORY_NAME + " DESC", null);
    }

Please provide your error. You could try to switch to:

String.format(" WHERE %s = '%s'", CATEGORY_SIGN, sign);

String.format("SELECT %s, %s, %s, %s FROM %s %s ORDER BY %s DESC, null, CATEGORY_ID, CATEGORY_NAME, CATEGORY_SIGN, CATEGORY_TABLE, signSelect, CATEGORY_NAME);

I think this is a bit cleaner, even though you could format it better in your IDE.

If sign is a string related to a TEXTual (e.g. varchar) column, you would need quotes around it in most DBMS.

public Cursor fetchAllCatagoryForSign(String sign) {
    String signSelect="";
    if(sign!=null){
        signSelect=" WHERE " + CATAGORY_SIGN + "='" + sign.Replace("'","''") + "'";
    }
    return mDb.rawQuery("SELECT " + CATAGORY_ID + "," +
            " " + CATAGORY_NAME +  "," +
            " " + CATAGORY_SIGN + " FROM "
            + CATAGORY_TABLE + signSelect + 
            " ORDER BY " + CATAGORY_NAME + " DESC", null);
}

@updated following GolezTrol's note

If category sign comes from a user from the world at large, this pieces of code would be open to SQL injection, in which case, you would want to protect the "sign" variable using .Replace as shown in the code.