MySQL联接多表错误

Question

I struggle to use join on multiple tables. When I try to do this:

SELECT `absences`.*, `employee`.*, `type`.*
FROM `absences`, `type`
 LEFT JOIN `login`.`employee` ON `absences`.`employee_FK` = `employee`.`employee_ID` 

I get this:

Unknown column 'absences.employee_FK' in 'on clause'

'absences.employee_FK' exists in my DB.

I want to display the user data and the type of the absence. How can I do that? I dont understand joins too well yet.

Answer 1

Looks like your just trying to join two tables, because you don't have a join condition for the type table in your query:

SELECT *
FROM absences
LEFT JOIN employee ON absences.employee_FK = employee.employee_ID

If you want to join to the type table too:

SELECT *
FROM absences
LEFT JOIN type ON absences.type_FK = type.type_ID
LEFT JOIN employee ON absences.employee_FK = employee.employee_ID

Answer 2

You have to select all the tables for using the JOIN condition.

The example goes like this:

SELECT `employee.*`, `absences.*`, `type.*`

FROM `employee`

JOIN `absences`

ON `employee`.`employee_ID` = `absences`.`employee_FK`

JOIN `type` 

ON `absences`.`type_FK` = `type`.`type_ID`

JOIN `on_off`

ON `on_off`.`on_off_ID` = `employee`.`on_off_FK`;

You can modify the query as per your requirement.

Answer 3

You have to use join for all tables:

SELECT `absences`.*, `employee`.*, `type`.*
FROM `absences`
 JOIN `type` on `absences`.`type_fk` = `type`.`type_ID`
 LEFT JOIN `login`.`employee` ON `absences`.`employee_FK` = `employee`.`employee_ID` 

Answer 4

You can work on the script below. Add Where clause at the end if necessary. Not tested...

SELECT * from absences a
inner join type t on (t.typeID = a.type_FK)
inner join employee e on (e.employee_ID = a.employee_FK)

Answer 5

This might be what you are looking for

select * from `absences` a
    left outer join `employee` e on e.`employee_ID` on a.`employee_FK`
    left outer join `type` t on t.`type_ID`=a.`type_FK`
    left outer join `on_off` o on o.`on_off_ID`=e.`on_off_FK`