Case Analysis of external join query in mysql

This article mainly explains the "mysql external join query case analysis", the content of the article is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in depth, together to study and learn "mysql external join query case analysis"!

Description

1. External connections not only return data rows that meet the join and query conditions, but also return some rows that do not meet the criteria.

2. If you want to leave the discarded records in the result set, you need to use an external join query.

In the inner join query, records that do not meet the criteria are discarded and do not appear in the result set.

3. External connections must use on to specify query criteria.

Example

SELECT O.IDDiO.ORDERPRONAMEFRON ORDERS OLEFT OUTER JOIN CUSTOMERS CON C.ID=O.CUSTOMER_ID UNION-- the keyword SELECT O.IDDiO.ORDERPRONAMEFROM ORDERS ORIGHT OUTER JOIN CUSTOMERS CON C.ID=O.CUSTOMER_ID Thank you for your reading, the above is the content of "mysql external join query instance Analysis". After the study of this article, I believe you have a deeper understanding of the problem of mysql external join query instance analysis, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!