UPDATE alert_tag <set> <if test="area_id != null and area_id != 0 "> area_id = #{area_id}, </if> <if test="tag_name != null and tag_name != '' "> tag_name = #{tag_name}, </if> <if test="tID != null and tID != '' "> tID = #{tID}, </if> <if test="addition != null and addition != '' "> addition = #{addition}, </if> <if test="api_key != null and api_key != '' "> api_key = #{api_key}, </if> <if test="ctime != null and ctime != '' "> ctime = #{ctime}, </if> <if test="alertState != null and alertState != '' "> alertState = #{alertState}, </if> <if test="alertContent != null and alertContent != '' "> alertContent = alertContent+"| closed by"+#{alertContent}, </if> </set> WHERE tID=#{tID} 哪里错误

这段SQL UPDATE语句中存在一个错误，即在 SET 子句中对 alertContent 进行赋值时，使用了加号 "+" 连接 alertContent 和字符串 " closed by" 及其后面的变量 #{alertContent}。这样写会导致语法错误，因为在 SET 子句中不能使用加号运算符。

正确的写法是使用 CONCAT 函数来将 alertContent 和字符串 " closed by" 及其后面的变量 #{alertContent} 进行连接，如下所示：

UPDATE alert_tag
SET
  area_id = #{area_id},
  tag_name = #{tag_name},
  tID = #{tID},
  addition = #{addition},
  api_key = #{api_key},
  ctime = #{ctime},
  alertState = #{alertState},
  alertContent = CONCAT(alertContent, ' closed by', #{alertContent})
WHERE tID = #{tID}

这样就能正确地将 alertContent 和字符串 " closed by" 及其后面的变量 #{alertContent} 进行连接了。