Question

我正在尝试制作一个简单的地图制作功能。我有一个包含地理坐标（“纬度”和“经度”），地名（“ feature_names”）和ISO-3166国家/地区代码（“ countrycodes”）的数据库。现在，我已经可以通过查询纬度/经度并让Folium制作我的地图来工作了，但是问题是，世界上有多个渥太华，温哥华，伦敦等。因此，引入了国家/地区代码以尝试缩小范围。

我的问题是我似乎无法使SQL查询返回任何内容。代码执行时不会抛出错误，但不会返回任何内容。 TL; DR：如何对数据库进行多个查询？

cur.execute("SELECT feature_name FROM WorldCities")
locnames = str(cur.fetchall())

cur.execute("SELECT country_code FROM WorldCities")
countrycodes = str(cur.fetchall())

def mapmaker():
location = input(prompt = "Where would you like to go? ")
country = input(prompt = "Great! Do you know which country this is in? ")

if not location:
    input(prompt = "Sorry, I didn't quite get that")

if location in locnames and country in countrycodes:

    #latquery = "SELECT latitude FROM WorldCities WHERE feature_name = ? AND country_code = ?"
    #lat = cur.execute(latquery, (location, ))
    latquery = cur.execute("SELECT latitude FROM WorldCities WHERE feature_name = ? AND country_code = ?", ((location,) (countrycodes,)))
    #lat = cur.execute(latquery, (location, + countrycodes))
    latloc = (latquery.fetchall())

    #longquery = "SELECT longitude FROM WorldCities WHERE feature_name = ?"
    #long = cur.execute(longquery, (location, ))
    #longloc = (long.fetchone())

    print(latloc) #longloc[0], country[0])
    #map = folium.Map(location=(latloc[0], longloc[0]), zoom_start=15)

    #return map
else:
    print ("Sorry, I didn't understand your query")

谢谢

Answer 1

数据库比简单的简单行列表更聪明。特别是，它可以包含索引以加速查询。如果不知道是否以及如何为数据库建立索引，就不可能优化查询。

如果数据库包含索引，则不应将其内容加载到平面列表中，而应使用直接查询。

话虽如此，您可以从一个查询中检索多个列，所以恕我直言，从表中提取地理坐标的正确方法应该是：

latlonquery = cur.execute("""SELECT latitude, longitude FROM WorldCities
WHERE feature_name = ? AND country_code = ?""", (location, countrycodes))
lat_lon = latlonquery.fetchone()
if lat_lon is not None:
    lat, lon = lat_lon
    print(lat, lon, location, country)
    ...

使用SQLite查询检索多个项目

1 个答案: