sql字符串替换(有点挑战···)

比如 有一字段为：
Num
6111
6201
6520
65121
60087
46300

我想把6开头的全都替换成5开头

注意这是表里的数据，我想用SQL语句实现替换

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SQL code:
update tb set
num = stuff(num,1,1,'5')
where num like '5%'

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SQL code:
update tb
set num=stuff(ltrim(num),1,1,'5')
where ltrim(num) like '6%'

---

SQL code:
-------------------------------------
-- Author : liangCK 梁爱兰
-- Comment: 小梁 爱 兰儿
-- Date : 2009-10-12 19:38:25
-------------------------------------

--> 生成测试数据: @tb
DECLARE @tb TABLE (Num int)
INSERT INTO @tb
SELECT 6111 UNION ALL
SELECT 6201 UNION ALL
SELECT 6520 UNION ALL
SELECT 65121 UNION ALL
SELECT 60087 UNION ALL
SELECT 46300

--SQL查询如下:

update @tb set
num = stuff(num,1,1,'5')
where num like '6%'

SELECT * from @tb

/*
Num
-----------
5111
5201
5520
55121
50087
46300

(6 行受影响)


*/

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一样的手误.将WHERE的5改为6

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或者SQL code:
updat