需求

当父节点id等于0时,父节点的名称显示为"一级系统部件"

解决方案

使用case when then

语法

CASE 字段

WHEN 条件1 THEN 值 1

WHEN 条件2  THEN 值 2

　　　[WHEN ...] 

　　　[ELSE 值] 

END  别名

实例

当父节点id等于0时,父节点的名称显示为"一级系统部件",其他显示为对应的名称

SELECT
    vc.id AS id,
    vc.`name` AS `name`,
    vc.parent_id AS parentId,
    CASE vc.parent_id WHEN 0 THEN '一级系统部件' ELSE a.`name` END parentName,
    vc.material_number AS materialNumber,
    vc.structure_type AS structureType,
    sd.`name` AS structureTypeName,
    vc.type AS type,
    vc.sort AS sort,
    vc.line_id AS lineId,
    b.`name` AS lineName,
    vc.`level` AS `level`,
    vc.remark AS remark 
FROM
    ((
            vehicle_component AS vc
            LEFT JOIN sys_dict AS sd ON sd.`code` = vc.structure_type 
            )
        LEFT JOIN vehicle_component AS a ON a.id = vc.parent_id 
    )
    LEFT JOIN line AS b ON b.id = vc.line_id 
WHERE
    vc.`status` = 1 
    AND vc.line_id = 49