MySQL的ExtractValue功能不起作用

Question

select extractvalue( SELECT CONCAT("'",(SELECT LCASE('<?xml version="1.0" encoding="utf-8" standalone="no"?>
<resp>
<dlrdtls>
<MessageId>43745973-737b-4c71-926f-797c0c9407a6</messageid>
<deliverystatus>failed</deliverystatus>
</dlrdtls>
</resp>')),"'"),'/resp/dlrdtls/messageid')  
as id ;

我想提取標記MessageId的值。

Answer 1

刪除內部SELECT語句，例如

SELECT EXTRACTVALUE(CONCAT("'",(LCASE('<?xml version="1.0" encoding="utf-8" standalone="no"?>
<resp>
<dlrdtls>
<MessageId>43745973-737b-4c71-926f-797c0c9407a6</messageid>
<deliverystatus>failed</deliverystatus>
</dlrdtls>
</resp>')),"'"),'/resp/dlrdtls/messageid')  
AS id ;

查詢以這種方式工作，但實際上也不需要CONCAT函數