SqlServer?oracle?mysql?
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SELECT   (CASE WHEN MBLL LIKE '%S%%'  ESCAPE   'S'  THEN CONVERT(NVARCHAR(100),REPLACE(MBLL,'%','')/100) ELSE MBLL  END ) [NEW_]    FROM   TABLE
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with tablea as (
select '80%' [mbll]
union all
select '76.5%' [mbll]
union all
select '80' [mbll]
union all
select '100' [mbll]
union all
select '>50' [mbll]
union all
select '>80%' [mbll]
union all
select '>0.580%' [mbll]
union all
select '>=0.580%' [mbll]
union all
select '<0.5' [mbll]
)
select *,(CASE WHEN MBLL LIKE '%S%%'  ESCAPE   'S'  THEN (CASE WHEN PATINDEX('%[0-9]%',mbll)=1 THEN CONVERT(NVARCHAR(100),CONVERT(decimal(20,6),REPLACE(mbll,'%',''))/100)  ELSE CONCAT(SUBSTRING(mbll,1,PATINDEX('%[0-9]%',mbll)-1) ,CONVERT(NVARCHAR(100),CONVERT(decimal(20,6),REPLACE(SUBSTRING(mbll,PATINDEX('%[0-9]%',mbll),LEN(mbll)),'%',''))/100)) END) ELSE CONVERT(NVARCHAR(100),MBLL) END )  [NEW]
from tablea
