Leetcode 175 Combine Two Tables SQL Pandas解法

题目

Easy

Table: Person

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| PersonId    | int     |
| FirstName   | varchar |
| LastName    | varchar |
+-------------+---------+

PersonId is the primary key column for this table.
Table: Address

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| AddressId   | int     |
| PersonId    | int     |
| City        | varchar |
| State       | varchar |
+-------------+---------+

AddressId is the primary key column for this table.

Write a SQL query for a report that provides the following information for each person in the Person table, regardless if there is an address for each of those people:

FirstName, LastName, City, State

解法

这道题需要注意的是不论有没有address，都需要返回person name，所以需要left join。

SQL

select p.FirstName, p.LastName, a.City, a.State
from Person p
left join address a
on p.PersonId = a.PersonId

Pandas

下面先用pandas建立了两个table, 然后通过 pd.merge 将两个table join在一起，how='left'来表示是left join。合并完两个table之后，选出需要返回的列。

import pandas as pd

person = pd.DataFrame([[1, "Wang", "Allen"]], columns=["PersonId", "LastName", "FirstName"])
address = pd.DataFrame([[1, 2, "New York City", "New York"]], columns=["AddressId", "PersonId", "City", "State"])

pd.merge(person, address, on='PersonId', how='left')[['LastName', 'FirstName', 'City', 'State']]