PHP left inner join, what is the difference between inner join and outer join
The difference between inner join and outer join: 1. The connection results are different. The connection result of the inner join only contains the rows that meet the connection conditions, while the connection result of the outer join contains the rows that meet the connection conditions; 2. The precautions are different. Inner joins need to pay attention to the difference between any and all used in nested queries. Outer joins do not need to be distinguished, and neither the left table nor the right table is restricted. This article Environment: Windows7 system, Dell G3 computer. The difference between inner join and outer join: The difference between inner join and outer join in the database mainly lies in the different connection results and different precautions, as follows: 1. The connection result is different The connection result of the inner connection only contains the rows that meet the connection conditions, and the two tables participating in the connection must meet the connection conditions; the connection result of the outer connection not only contains the rows that meet the conditions Rows with join conditions, and rows that do not meet their own conditions, including left outer joins, right outer joins, and full outer…
What is the difference between inner join and outer join?
Difference: the inner join query operation lists the data rows that match the join conditions; the outer join, returns to the query result set not only contains the rows that meet the join conditions, but also includes the left table (left outer join) , all data rows in the right table (right outer join), or both edge join tables (full outer join). The connection of two tables is established by linking one or more columns in one table with columns in the other table. The expressions used to join two tables form the join condition. When the connection is successful, the data in the second table is connected with the first table, and a composite result set is formed-including the plan of the data rows in the two tables. Simply put, there are subsets of the two tables, although only temporarily There are two basic types of connections, inner and outer connections. The main difference between the two types is that an outer join will return rows in the result set even if the join conditions are not satisfied, while an inner join will not return rows in the result set class When the external connection does not meet the…