68 lines
1.5 KiB
Markdown
68 lines
1.5 KiB
Markdown
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* [175. Combine Two Tables](#175-combine-two-tables)
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* [未完待续...](#未完待续)
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# 175. Combine Two Tables
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https://leetcode.com/problems/combine-two-tables/description/
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## Describe
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Table: Person
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```html
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+-------------+---------+
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| Column Name | Type |
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+-------------+---------+
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| PersonId | int |
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| FirstName | varchar |
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| LastName | varchar |
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+-------------+---------+
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PersonId is the primary key column for this table.
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```
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Table: Address
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```html
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+-------------+---------+
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| Column Name | Type |
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+-------------+---------+
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| AddressId | int |
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| PersonId | int |
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| City | varchar |
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| State | varchar |
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+-------------+---------+
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AddressId is the primary key column for this table.
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```
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取出 FirstName, LastName, City, State 数据，而不管一个用户有没有填地址信息。
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## SQL Schema
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```sql
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CREATE TABLE Person ( PersonId INT, FirstName VARCHAR ( 255 ), LastName VARCHAR ( 255 ) );
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CREATE TABLE Address ( AddressId INT, PersonId INT, City VARCHAR ( 255 ), State VARCHAR ( 255 ) );
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TRUNCATE TABLE Person;
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INSERT INTO Person ( PersonId, LastName, FirstName )
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VALUES
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( 1, 'Wang', 'Allen' );
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TRUNCATE TABLE Address;
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INSERT INTO Address ( AddressId, PersonId, City, State )
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VALUES
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( 1, 2, 'New York City', 'New York' );
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```
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## Solution
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使用左外连接。
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```sql
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SELECT FirstName, LastName, City, State
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FROM Person AS p LEFT JOIN address AS a
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ON p.PersonId = a.PersonId;
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```
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# 未完待续...
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