Question

我在如何在此查询中显示所有空值时遇到困难

这是我的SQL fiddle。

 SELECT project_staff_assignment.taxemployee_id, taxemployee.nickname
  FROM taxemployee 
  LEFT JOIN project_staff_assignment ON project_staff_assignment.taxemployee_id = taxemployee.id
 WHERE taxemployee.id = 4

我想看到的还显示其他员工的空值

Answer 1

可能是这样的

SELECT project_staff_assignment.taxemployee_id, taxemployee.nickname
FROM taxemployee 
LEFT JOIN project_staff_assignment ON project_staff_assignment.taxemployee_id = taxemployee.id
WHERE taxemployee.id = 4 OR project_staff_assignment.taxemployee_id IS NULL

<强> FIDDLE DEMO

Answer 2

如果我理解正确，this就是您所需要的。删除condtion。它将仅返回1条记录，因为您明确过滤了id = 4

 SELECT project_staff_assignment.taxemployee_id, taxemployee.nickname
  FROM taxemployee 
  LEFT JOIN project_staff_assignment ON project_staff_assignment.taxemployee_id = taxemployee.id

UPDATED FIDDLE

 SELECT 
CASE project_staff_assignment.taxemployee_id WHEN '4' THEN project_staff_assignment.taxemployee_id ELSE NULL END AS REQUIRED_FIELD,
taxemployee.id,`EmployeeNumber`, `Fullname`, `Nickname`,`Position`, `level`
  FROM taxemployee 
  LEFT  JOIN project_staff_assignment  ON project_staff_assignment.taxemployee_id = taxemployee.id

正在做的是，选择所有记录，并使用CASE STATEMENT，如果值= 4，则显示为4，否则显示为NULL。

MYSQL显示左边的Null员工加入

2 个答案: