Скачать или смотреть Understanding the LEFT OUTER JOIN for Linking Vendor and Quotations Tables in MySQL

Discover how to efficiently link two tables in MySQL through `LEFT OUTER JOIN`, enabling multiple quotations per vendor. Learn the basics of inserting data across both tables for your database structure.
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This video is based on the question https://stackoverflow.com/q/63001110/ asked by the user 'Fahad Azeem' ( https://stackoverflow.com/u/10415786/ ) and on the answer https://stackoverflow.com/a/63001357/ provided by the user 'Spinassi' ( https://stackoverflow.com/u/11161908/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Challenge of Interlinked Tables in MySQL

Creating a relational database often involves interlinking multiple tables, especially when one piece of information can reference many related values. In this post, we’ll explore a common scenario involving a Vendor table and a Quotations table in MySQL. If you’re experiencing difficulties in linking these tables or managing data inputs, don’t worry – we’ve got you covered!

The Problem

Imagine you are tasked with setting up two tables:

A Vendor Table that lists various vendors along with their details.

A Quotations Table that captures multiple monthly quotations for each vendor.

Here's a breakdown of the structure you need:

Vendor Table

Vendor IDVendor NamePartner NameQuotations1XYZ CompanyXYZ Partner(click to view quotations)When a user clicks to view quotations, they should see something like:

[[See Video to Reveal this Text or Code Snippet]]

Quotations Table

Quotation NoMonthFILE1JuneDOWNLOAD (.PDF)2JulyDOWNLOAD (.PDF)The Issue at Hand

You might be wondering:

How to correctly use a LEFT OUTER JOIN to link these tables, especially since each vendor can have multiple quotations.

What the best approach is for inserting data into both tables.

The Solution

Let’s break down the solution into clear sections:

Using LEFT OUTER JOIN

To link the Vendor table to the Quotations table so that a vendor can have multiple quotations, you should use the LEFT OUTER JOIN. Here’s why:

LEFT OUTER JOIN: This type of join returns all records from the left table (Vendor table) and matched records from the right table (Quotations table). If no match is found, NULL values will appear in the result set for the quotations.

Example Query:

[[See Video to Reveal this Text or Code Snippet]]

This query will allow you to list all vendors, even those without quotations, and display the available quotations alongside.

Choosing the Right Join

If you want to see only those vendors that have quotations, opt for an INNER JOIN, which excludes vendors without entries in the Quotations table. It’s crucial to determine your desired output before selecting the type of join.

Inserting Data into Both Tables

Now that you're linked up, you need to insert data effectively in both tables. Here’s how you can manage this using basic SQL INSERT statements:

Inserting into Vendor Table:

[[See Video to Reveal this Text or Code Snippet]]

Inserting into Quotations Table:
After ensuring there’s a vendor available, insert quotations as follows:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

In summary, connecting your Vendor and Quotations tables in MySQL is straightforward once you understand the appropriate use of joins and data insertion methods. The LEFT OUTER JOIN is beneficial for maintaining an inclusive view of vendors, while separate INSERT statements allow you to build your records efficiently.

Following this guide, you should be well-equipped to tackle your MySQL table interlinking challenges. Happy coding!