Oracle中编写多返回值CASE WHEN语句报缺失关键字错误如何解决

SELECT 
  login_id,
  CASE WHEN login_id = 'Thomas' THEN lastnm ELSE Secondarylastnm END AS lastname,
  CASE WHEN login_id = 'Thomas' THEN ssn ELSE Secondaryssn END AS SocialSecurityNumber
FROM Employees;

• 单个CASE WHEN是单行单值表达式，一次只能返回一个值，无法同时返回两个字段的结果，需要针对lastname和SocialSecurityNumber两个字段分别写独立的CASE WHEN逻辑
• 别名AS语法要放在整个CASE WHEN ... END结构的后面，不能写在THEN/ELSE子句内部
• ELSE关键字后面不需要再加THEN，属于语法冗余触发了缺失关键字报错

内容的提问来源于stack exchange，提问作者challengeAccepted