这两个SQL语句有什么区别？-- 执行速度一个是3分钟，一个是1秒钟

[rabbityin]

主要目的是字段 PAPER_MAIN_NAME.m905 和字段 PAPER_INFO.collection

满足：PAPER_MAIN_NAME.m905 = '$c' + PAPER_INFO.collection 的记录是需要的。

SQL如下：

update PAPER_MAIN_NAME set PAPER_MAIN_NAME.m211 = '$a0376'
where PAPER_MAIN_NAME.m001 in (
select PAPER_MAIN_NAME.m001 from PAPER_MAIN_NAME,PAPER_INFO
where char_length(PAPER_MAIN_NAME.m905) > 3 and
substring(PAPER_MAIN_NAME.m905,1,2)='$c' and
substring(PAPER_MAIN_NAME.m905,3,char_length(PAPER_MAIN_NAME.m905)-2)=PAPER_INFO.collection and
PAPER_INFO.kernel = '2' and
substring(PAPER_INFO.paper_class_num,1,1) ='T'
)
---------------------------------------------------------------
update PAPER_MAIN_NAME set PAPER_MAIN_NAME.m211 = '$a0376'
where PAPER_MAIN_NAME.m001 in (
select PAPER_MAIN_NAME.m001 from PAPER_MAIN_NAME,PAPER_INFO
where char_length(PAPER_MAIN_NAME.m905) > 3 and
PAPER_MAIN_NAME.m905 = '$c' + PAPER_INFO.collection and
PAPER_INFO.kernel = '2' and
substring(PAPER_INFO.paper_class_num,1,1) ='T'
)
---------------------------------------------------------------
这两个SQL语句有什么区别？

执行速度一个是3分钟
一个是1秒钟

为什么?