Get the solution ↓↓↓
I'm implementing a Tag system using PHP and MySql.
In my Tags table there are two columns (Id and Tag). Each Id may have one or more tag(s) associated to it - like this:
| Id | Tag |
|---|---|
| 1 | red |
| 1 | blue |
| 1 | orange |
| 2 | green |
| 3 | black |
| 4 | grey |
| 5 | grey |
| 6 | pink |
| 7 | white |
| 7 | purple |
| 8 | blue |
| 9 | yellow |
| 9 | cyan |
UseNOT EXISTS to filter out duplicate tags and aggregate:
SELECT t1.Id, MAX(t1.Tag) Tag
FROM Tags t1
WHERE NOT EXISTS (
SELECT 1
FROM Tags t2
WHERE t2.Id > t1.Id AND t2.Tag = t1.Tag
)
GROUP BY t1.Id
ORDER BY t1.Id DESC
Instead ofMAX() you could useMIN() or
See the demo.
Create a temp table with unique constraint and do insert ignore.
DROP Temporary table IF exists T_Test;
create Temporary table T_Test(id INTEGER UNIQUE, tag VARCHAR(10) UNIQUE);
insert IGNORE into T_Test
SELECT * FROM Tags
ORDER BY id DESC, tag DESC;
SELECT * from T_Test;
Our community is visited by hundreds of web development professionals every day. Ask your question and get a quick answer for free.
Find the answer in similar questions on our website.
Do you know the answer to this question? Write a quick response to it. With your help, we will make our community stronger.
PHP (from the English Hypertext Preprocessor - hypertext preprocessor) is a scripting programming language for developing web applications. Supported by most hosting providers, it is one of the most popular tools for creating dynamic websites.
The PHP scripting language has gained wide popularity due to its processing speed, simplicity, cross-platform, functionality and distribution of source codes under its own license.
https://www.php.net/
DBMS is a database management system. It is designed to change, search, add and delete information in the database. There are many DBMSs designed for similar purposes with different features. One of the most popular is MySQL.
It is a software tool designed to work with relational SQL databases. It is easy to learn even for site owners who are not professional programmers or administrators. MySQL DBMS also allows you to export and import data, which is convenient when moving large amounts of information.
https://www.mysql.com/
Welcome to the Q&A site for web developers. Here you can ask a question about the problem you are facing and get answers from other experts. We have created a user-friendly interface so that you can quickly and free of charge ask a question about a web programming problem. We also invite other experts to join our community and help other members who ask questions. In addition, you can use our search for questions with a solution.
Ask about the real problem you are facing. Describe in detail what you are doing and what you want to achieve.
Our goal is to create a strong community in which everyone will support each other. If you find a question and know the answer to it, help others with your knowledge.