SQL Server T-SQL table connections

A Cartesian product

SELECT * FROM table 1, table 2

Traverse the records of two tables to display

Horizontal connection of two tables

1 using foreign key relationships as a condition

SELECT * from table 1, table 2 where table 1 table 2 foreign KEY constraint relationship

Select column 1, column 2, from table 1, table 2 where table 1 foreign KEY constraint relationship for table 2

2 Join on

SELECT * FROM table 1 join table 2 on table 1 table 2 foreign KEY constraint relationship

Select column 1, column 2 from table 1 join table 2 on table 1 foreign KEY constraint relationship for table 2

The LEFT JOIN table is the main table when it joins

The right join table is connected with the table as the main --draw one record with one table to determine the combination with another table, the same duplicate extraction, no display null

Vertical connection of three tables

Union

Select column from table 1 Union Select column from table 2

--The columns to be concatenated must have the same column name, and the data types are equal

SQL Server T-SQL table connections