MySQL 选择所有数据包括另一个表，即使为空
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Select all data include another table even if null
提问by Jordan
Setup: (1) Employee table (employeeID, firstName, lastName)
设置：（1）员工表（employeeID、firstName、lastName）
(1) Shoe table (shoeID, Employee_employeeID, shoeName, shoeColor, shoeBrand)
(1) 鞋表（shoeID、Employee_employeeID、shoeName、shoeColor、shoeBrand）
I want to select all rows in Employee table and even if there is no matching EmployeeID (Employee_EmployeeID) in the shoe table display that entire row anyway. Example desired output:
我想选择 Employee 表中的所有行，即使鞋表中没有匹配的 EmployeeID (Employee_EmployeeID) 也会显示整行。示例所需的输出：
EmployeeID | firstName | lastName | shoeName | shoeColor | shoeBrand
1 John Smith AirMax2 Red Nike
2 Ronald Mcdonald null null null
3 James Knight null null null
4 Cindy Smith Pump Brown Cole Haan
I have tried a lot of different joins and I will get duplicate rows for each Employee.
我尝试了很多不同的连接，我会为每个员工获得重复的行。
回答by echo_Me
try this
尝试这个
SELECT e.employeeId,e.firstName,e.lastName,s.ShoeName,s.ShoeColor,s.ShoeBrand
FROM Employee e
LEFT JOIN Shoe s
ON e.employeeID = s.Employee_employeeID
回答by Gordon Linoff
You need a left outer join:
你需要一个left outer join：
select e.employeeid, e.firstname, e.lastname, s.shorname, s.shoecolor, s.shoebrand
from employee e left outer join
shoe s
on e.employeeid = s.employeeid
回答by Taryn
You are going to want to use a LEFT JOIN:
你会想要使用一个LEFT JOIN：
select e.employeeId,
e.firstName,
e.lastName,
s.ShoeName,
s.ShoeColor,
s.ShoeBrand
from Employee e
left join shoe s
on e.employeeID = s.Employee_employeeID
A LEFT JOINwill return the matching rows from the employeetable even if there is not a matching row in the shoetable.
即使表中没有匹配的行，ALEFT JOIN也会从employee表中返回匹配的行shoe。
If you need help learning JOINsyntax, here is a great visual explanation of joins.
如果您需要帮助学习JOIN语法，这里是joins 的一个很好的视觉解释。
Now, if you wanted all rows that match both tables, then you would use an INNER JOIN.
现在，如果您想要匹配两个表的所有行，那么您可以使用INNER JOIN.
