Finding duplicate values in a SQL table

The following example uses ipython-sql. To install:
pip install ipython-sql

%sql is a Jupyter magic command and can be ignored when not using Jupyter notebooks.

Configure SQL for Jupyter notebook

#Load sql
%load_ext sql
#connect to sqlite
%sql sqlite://

Create a table

CREATE TABLE players2 (first_name, last_name, age);
INSERT INTO players2 (first_name, last_name, age) VALUES
('Lebron', 'James', 33),
('Steph', 'Curry', 30),
('Mike', 'Jordan', 55),
('Mike', 'Bibby', 40);
SELECT * FROM players2
first_name last_name age
Lebron James 33
Steph Curry 30
Mike Jordan 55
Mike Bibby 40

Find duplicate values in SQL table based on single column

--Select all duplicate first names, and return the count
SELECT first_name, COUNT(first_name)
FROM players2
GROUP BY first_name
HAVING COUNT(first_name) > 1
first_name COUNT(first_name)
Mike 2

Create another table


CREATE TABLE players3 (first_name, last_name, age);
INSERT INTO players3 (first_name, last_name, age) VALUES
('Lebron', 'James', 33),
('Steph', 'Curry', 30),
('Mike', 'Jordan', 55),
('Mike', 'Bibby', 40),
('Mike', 'Smith', 40);

Find duplicate values in SQL table based on multiple columns

--Where both first_name and age are duplicates,
--here should return Mike with a count of two, since there are two 40 year old Mikes
first_name, age, COUNT(*)
first_name, age
COUNT(*) > 1
 * sqlite:// 
first_name age COUNT(*)
Mike 40 2

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