sql-server-2008 - SQL Query 根据从 2 个表中的引用从第二个表中提取列值

Question

对不起，我试图寻找答案并被卡住了

我正在尝试内部连接两个表以提取一个值，例如

table 1
--------
column a
column b
column c

table 2
--------
column a
column d

所以，我想从 table 1 中提取所有列然后，在哪里 column a出现在 table 2 ，我要拉 column d
只是不确定内部连接是否正确或如何编写它

Answer 1

有四种类型的连接:

JOIN: Return rows when there is at least one match in both tables
LEFT JOIN: Return all rows from the left table, even if there are no matches in the right table
RIGHT JOIN: Return all rows from the right table, even if there are no matches in the left table
FULL JOIN: Return rows when there is a match in one of the tables

如 http://www.w3schools.com/sql/sql_join.asp 所列

你想从你的描述中加入 LEFT JOIN

SELECT table1.*, table2.d FROM table1 LEFT JOIN table2 ON table1.a = table2.a