SQLite更新表

/**
     * 判断某表里某字段是否存在
     *
     * @param db
     * @param tableName
     * @param fieldName
     * @return
     */
    public boolean isFieldExist(SQLiteDatabase db, String tableName, String fieldName) {
        String queryStr = "select sql from sqlite_master where type = 'table' and name = '%s'";
        queryStr = String.format(queryStr, tableName);
        Cursor c = db.rawQuery(queryStr, null);
        String tableCreateSql = null;
        try {
            if (c != null && c.moveToFirst()) {
                tableCreateSql = c.getString(c.getColumnIndex("sql"));
            }
        } finally {
            if (c != null)
                c.close();
        }
        if (tableCreateSql != null && tableCreateSql.contains(fieldName))
            return true;
        return false;
    }
 
/**更新table_name表 增加field_name字段**/
            if (!dbHelper.isFieldExist(db, "table_name", "field_name")) {
                db.execSQL("ALTER TABLE table_name ADD COLUMN field_name varchar(50)");
            }