SQL
  • Tips
  • SQL
    • Database Basics
    • SQL Basics
    • SQL Syntax
    • Retrieve Data: SELECT
    • Sort Data: ORDER BY
    • Filter Data: WHERE
    • Calculated Fields
    • Aggregate Functions
    • Group Data: GROUP BY
    • Subqueries
    • Join Tables
    • Combine Queries: UNION
    • Control Flow Statements
    • IF function
    • Handle NULL
    • Date
    • Numeric
    • String
    • Notes
  • Table/Database
    • Insert
    • Delete
    • Update
    • Table
    • Database
    • Stored Procedure
  • Misc
    • SQL vs NoSQL
    • 大数据
    • Why SQL instead of Excel + VBA?
  • sqlzoo
    • world table
    • nobel table
    • football data
    • movie data
    • Teacher Department Data
    • Edinburgh Buses data
  • Leetcode
    • 175_Combine Two Tables
    • 176_Second Highest Salary
    • 177_Nth Highest Salary
    • 178_Rank Scores
    • 180_Consecutive Numbers
    • 181_Employees Earning More Than Their Managers
    • 182_Duplicate Emails
    • 183_Customers Who Never Order
    • 184_Department Highest Salary
    • 185_Department Top Three Salaries
    • 196_Delete Duplicate Emails
    • 197_Rising Temperature
    • 570_Managers with at Least 5 Direct Reports
    • 578_Get Highest Answer Rate Question
    • 579_Find Cumulative Salary of an Employee
    • 584_Find Customer Referee
    • 586_Customer Placing the Largest Number of Orders
    • 595_Big Countries
    • 596_Classes More Than 5 Students
    • 597_Friend Requests I: Overall Acceptance Rate
    • 601_Human Traffic of Stadium
    • 602_Friend Requests II: Who Has the Most Friends
    • 603_Consecutive Available Seats
    • 607_Sales Person
    • 608_Tree Node
    • 610_Triangle Judgement
    • 612_Shortest Distance in a Plane
    • 613_Shortest Distance in a Line
    • 619_Biggest Single Number
    • 620_Not Boring Movies
    • 626_Exchange Seats
    • 627_Swap Salary
  • Facebook 面经题
    • spam filter
    • marketplace
    • instagram
    • session
    • message confirmation
Powered by GitBook
On this page

Was this helpful?

  1. Leetcode

196_Delete Duplicate Emails

Write a SQL query to delete all duplicate email entries in a table namedPerson, keeping only unique emails based on its smallest Id.

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
| 3  | john@example.com |
+----+------------------+
Id is the primary key column for this table.

For example, after running your query, the abovePersontable should have the following rows:

+----+------------------+
| Id | Email            |
+----+------------------+
| 1  | john@example.com |
| 2  | bob@example.com  |
+----+------------------+

Solution: self join

DELETE p1 
FROM Person AS p1,
     Person AS p2
WHERE
    p1.Email = p2.Email 
    AND p1.Id > p2.Id
Previous185_Department Top Three SalariesNext197_Rising Temperature

Last updated 5 years ago

Was this helpful?