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This article mainly introduces the differences between internal connection and external connection, which can be used for reference by interested friends. I hope you will gain a lot after reading this article.

The difference between inner join and outer join: 1, the connection result of inner connection contains only the rows that meet the connection conditions, while the connection result of outer connection contains rows that meet the connection conditions; 2, the matters needing attention are different, so the inner join needs to pay attention to the difference between any and all used in the nested query, the outer join does not need to be distinguished, and the left table and right table are not restricted.

The difference between internal and external connections:

The difference between internal connections and external connections in the database mainly lies in the different connection results and considerations, as shown below:

1. The connection results are different.

The join result of the inner join contains only the rows that meet the join conditions, and the two tables participating in the join must meet the join conditions, while the join result of the outer connection includes not only the rows that meet the join conditions, but also the rows that do not meet their own conditions. it also includes left outer join, right outer join and full outer join.

2. Different points for attention

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, the left and right tables are not restricted, and all records show that the deficiencies of the two tables can be filled with null.

The inner join refers to the most common equivalent join; the left outer join refers to the same as the right outer connection on the basis of the equivalent join, plus the unmatched data in the main table; and the full outer join refers to the addition of the unmatched data in the left table and right table on the basis of the equivalent join.

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