是否可以将MySQL中select exists查询的值分配给存储过程中的多个变量？

Question

set sender_id =（选择EXISTS（SELECT 1 FROM account WHERE account_id = p_sender_id））;

set viewer_id =（选择EXISTS（SELECT 1 FROM account WHERE account_id = p_viewer_id））;

Answer 1

您可以执行以下操作：

SELECT EXISTS(SELECT 1 FROM account WHERE account_id = p_sender_id)),
       EXISTS(SELECT 1 FROM account WHERE account_id = p_viewer_id))
INTO sender_id, viewer_id;

详细了解SELECT...INTO。

重新评论：

如果要运行一个子查询来设置两者：

SELECT
  MAX(CASE account_id WHEN p_sender_id THEN 1 ELSE 0 END),
  MAX(CASE account_id WHEN p_viewer_id THEN 1 ELSE 0 END)
INTO sender_id, viewer_id 
FROM account
WHERE account_id IN (p_sender_id, p_viewer_id);