Summary: in this tutorial, you will learn how to find duplicate values of one or more columns in MySQL. Data duplication happens because of many reasons. Finding duplicate values is one of the important tasks that you must deal with when working with the databases. This chapter describes how to obtain and install MySQL. A summary of the procedure follows and later sections provide the details. If you plan to upgrade an existing version of MySQL to a newer version rather than install MySQL for the first time, see Section 2.11, “Upgrading MySQL”, for information about upgrade procedures and about issues that you should consider before upgrading. Now click on below button for MySQL download. Download MySQL Full Setup offline installer standalone. This version of MySQL works for Both 32 Bit and 64 Bit versions of Windows 8, Windows 7 etc. The first button is to download MySQL for Windows. Second button is to download MySQL for Mac OS. MySQL is especially popular on the web. It is one part of the very popular LAMP platform consisting of Linux, Apache, MySQL, and PHP. Currently MySQL is owned by Oracle. MySQL database is available on most important OS platforms. It runs on BSD Unix, Linux, Windows or Mac OS. MySQL comes in two versions: MySQL server system and MySQL embedded. The following is an example walkthrough of importing an Excel document into a MySQL database. To run this tutorial you will need an Excel file, and admin access to a running MySQL instance. For the example we’ll be using the following Excel file on rental boats: boats.xlsx.
Summary: in this tutorial, you will learn how to find duplicate values of one or more columns in MySQL.
Photo album templates for photoshop. Data duplication happens because of many reasons. Finding duplicate values is one of the important tasks that you must deal with when working with the databases.
Setting up a sample table
First, create a table named
contacts with four columns:
Second, inserts rows into the
Third, query data from the contacts table:
contacts table, we have some rows that have duplicate values in the
Find duplicate values in one column
The find duplicate values in on one column of a table, you use follow these steps:
- First, use the
GROUP BYclause to group all rows by the target column, which is the column that you want to check duplicate.
- Then, use the
COUNT()function in the
HAVINGclause to check if any group have more than 1 element. These groups are duplicate.
The following query illustrates the idea:
By using this query template, you can to find rows that have duplicate emails in the
contacts table as follows:
This picture shows the output of the query that shows the duplicate emails:
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Find duplicate values in multiple columns
Sometimes, you want to find duplicate rows based on multiple columns instead of one. In this case, you can use the following query:
Rows are considered duplicate only when the combination of columns are duplicate therefore we used the
AND operator in the
For example, to find rows in the
contacts table with duplicate values in
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The following illustrates the output of the query:
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In this tutorial, you have learned how to find duplicate rows based on value of one or more columns in MySQL.