mysql - 使用基于其他列的值的临时列进行选择

Question

我有一个 mysql 表，其架构类似于下面的 json 数组。

[
    { "id": 1, "firstName": "Charles Montgomery", "lastName": "Burns", "managerId": 12},
    { "id": 2, "firstName": "Bart", "lastName": "Simpson", "managerId": 1},
    { "id": 3, "firstName": "Marge", "lastName": "Simpson", "managerId": 1},
    { "id": 4, "firstName": "Lisa", "lastName": "Simpson", "managerId": 1},
    { "id": 5, "firstName": "Maggie", "lastName": "Simpson", "managerId": 1},
    { "id": 6, "firstName": "Homer", "lastName": "Simpson", "managerId": 4},
    { "id": 7, "firstName": "Ned", "lastName": "Flanders", "managerId": 4},
    { "id": 8, "firstName": "Krusty", "lastName": "The Clown", "managerId": 2},
    { "id": 9, "firstName": "Waylon", "lastName": "Smithers", "managerId": 2},
    { "id": 10, "firstName": "Ralph", "lastName": "Wiggum", "managerId": 5},
    { "id": 11, "firstName": "Itchy", "lastName": "", "managerId": 5},
    { "id": 12, "firstName": "Comic Book Guy", "lastName": "", "managerId": 4}
]

managerId 字段是 id 字段的自引用外键。

我需要进行一个查询，该查询将使用根据 id 字段计算出的“managerName”动态添加列，该字段将包含串联的 firstName 和 lastName。

下面是我试过的(简化的)查询。问号是由 mysql driver 填充的占位符(在 nodejs 中):

SELECT * , 
(SELECT CONCAT_WS(' ', firstName, lastName) FROM employee WHERE managerId = id ) as managerName
FROM employee WHERE employee.id = ?;

我意识到这个 WHERE managerId = id 是要查看的地方，但老实说我不知道​​要放置什么条件才能匹配正确的值。

有人可以帮忙吗？

编辑万一有人偶然发现同样的事情，我发现了 helpful article .连例子都是相似的。

Answer 1

LEFT JOIN 是您的 friend 。 tra 使用这样的查询:

SELECT 
    e.*,
    CONCAT_WS(' ', m.firstName, m.lastName) AS managerName
FROM employee e WHERE e.employee.id = ?
LEFT JOIN  employee m ON e.managerId = m.id;