SQL table connection basic syntax and SQL connection basic syntax

SQL table connection basic syntax and SQL connection basic syntax

SQL connections can be divided into internal connections, external connections, and cross connections.

1. Inner join: the inner join query operation lists the data rows that match the connection condition. It uses the comparison operator to compare the column values of the connected columns.

1.1 select * from Table1 as a, Table2 as B where a. id = B. id

1.2 select * from Table1 as a inner join Table2 as B on a. id = B. id

2.3 Full join (when a row does not match a row in another table, the selection list column of the other table contains a null value. If there are matched rows between tables, the entire result set row contains the data value of the base table)

Select * from Table1 as a full outer join Table2 as B on a. id = B. id

3. Combine each row in the left table with all rows in the right table. Cross join is also called Cartesian product.

Select * from Table1 as a cross join Table2 as B order B a. id

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