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Editor to share with you how to carry out joint query in navicat, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

Cartesian product

Multi-table queries, separated by commas between table names. In this way, all the data in multiple tables will be checked out, and the way to find out is the way of Cartesian product (complete combination).

Many of the data found in this way are invalid. You can add conditions to a multi-table query to find the information you want.

Internal connection

Valid information can be filtered through the associated attributes between tables when designing the database.

Explicit internal connection

SELECT * FROM employee AS E1, enterprise AS e2 WHERE e1.enterpriseId-e2.id

Implicit internal connection

SELECT * FROM employee E1 INNER JOIN enterprise e2 ON e1.enterpriseId=e2.id

There is no essential difference between implicit and explicit internal joins.

External connection

Based on one table, all the data in this table is checked out, and then it is associated with another table. If it is associated with it, its information is displayed, and if it is not associated, it is not displayed as null.

Left outer connection

SELECT * FROM employee E1 LEFT JOIN enterprise e2 ON e1.enterpriseId=e2.id

Right outer connection

SELECT * FROM employee E1 RIGHT JOIN enterprise e2 ON e1.enterpriseId=e2.id

Alias of the table

There are two reasons to use aliases for tables:

1. For convenience and simplicity.

two。 If you are making a multiple table query from a duplicate table, you must use an alias.

There are two ways to use aliases:

1. Just add a space after the name of the table and give it a new name.

SELECT * FROM employee E1, enterprise e2 WHERE e1.enterpriseId-e2.id

2.as is no different from naming it directly, but it looks like a more standard sql statement will be easier to see.

SELECT * FROM employee AS E1, enterprise AS e2 WHERE e1.enterprise navicat e2.id; above is all the content of this article entitled "how to federate query in enterprise? thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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