Database daily question --- day 10: combine two tables

One 、 Problem description

surface

: 

Person

+-------------+---------+
|  Name  |  type  |
+-------------+---------+
| PersonId | int |
| FirstName | varchar |
| LastName | varchar |
+-------------+---------+
personId  Is the primary key column of the table .
This table contains some people's  ID  And their last and first names .


surface

: 

Address

+-------------+---------+
|  Name  |  type  |
+-------------+---------+
| AddressId | int |
| PersonId | int |
| City | varchar |
| State | varchar |
+-------------+---------+
addressId  Is the primary key column of the table .
Each row of the table contains a  ID = PersonId  Information about people's cities and states .


Write a SQL Query to report  

Person

  The last name of each person in the list 、 name 、 Cities and states . If  

personId

  Your address is not in  

Address

  In the table , The report is empty  

null

 .

With  

In any order

  Return result table .

Topic link ：

Combine two tables

Two 、 Subject requirements

Examples

Input : 
Person surface :
+----------+----------+-----------+
| personId | lastName | firstName |
+----------+----------+-----------+
| 1 | Wang | Allen |
| 2 | Alice | Bob |
+----------+----------+-----------+
Address surface :
+-----------+----------+---------------+------------+
| addressId | personId | city | state |
+-----------+----------+---------------+------------+
| 1 | 2 | New York City | New York |
| 2 | 3 | Leetcode | California |
+-----------+----------+---------------+------------+
Output : 
+-----------+----------+---------------+----------+
| firstName | lastName | city | state |
+-----------+----------+---------------+----------+
| Allen | Wang | Null | Null |
| Bob | Alice | New York City | New York |
+-----------+----------+---------------+----------+
explain : 
There is no  personId = 1  The address of , So their cities and States return  null.
addressId = 1  Contains  personId = 2  Address information for .


Investigate

1. Table joins
2. It is recommended to use time 10~25min


3、 ... and 、 Problem analysis

This question is a question about the basis of connection , I put

SQL

Here are some common languages ：

• A inner join B： Internal connection , intersect

• A left join B： The left outer join , take A All ,B There is no corresponding value , Then for
  null

• A right join B： Right connection , take B All ,A There is no corresponding value , Then for
  null

• A full outer join B： Full outer join , Union and collection , There is no corresponding value for each other
  null

This question , Let's take a look at the requirements of the topic ： Two tables  

Person

、

Address

, If the address number on the right does not appear in the table on the left , Set directly to null.

So which connection method to choose , It's obvious . Simply select the left outer connection , All at once

readily solved

.

Four 、 coded

select p.firstName,p.lastName,a.city,a.state
from Person p
left join Address a on p.personId=a.personId


5、 ... and 、 test result