Try

CASE WHEN ebv.db_no IN (22978,23218,23219) THEN 'WECS 9500' ELSE 'WECS 9520' END

UPDATE table_name 
  SET column_name=CASE 
WHEN column_name in ('value1', 'value2',.....) 
  THEN 'update_value' 
WHEN column_name in ('value1', 'value2',.....) 
  THEN 'update_value' 
END

table_name =需要操作的表名。

column_name =需要设置的列名/字段名。

update_value =需要设置的column_name的值

Select s.stock_code,s.stock_desc,s.stock_desc_ar,
mc.category_name,s.sel_price,
case when s.allow_discount=0 then 'Non Promotional Item' else 'Prmotional 
item' end 'Promotion'
From tbl_stock s inner join tbl_stock_category c on s.stock_id=c.stock_id
inner join tbl_category mc on c.category_id=mc.category_id
where mc.category_id=2 and s.isSerialBased=0 

select id,phno,case gender
when 'G' then 'M'
when 'L' then 'F'
else
'No gender'
end
as gender 
from contacts

这种格式要求你使用:

CASE ebv.db_no 
  WHEN 22978 THEN 'WECS 9500' 
  WHEN 23218 THEN 'WECS 9500'  
  WHEN 23219 THEN 'WECS 9500' 
  ELSE 'WECS 9520' 
END as wecs_system 

否则,使用:

CASE  
  WHEN ebv.db_no IN (22978, 23218, 23219) THEN 'WECS 9500' 
  ELSE 'WECS 9520' 
END as wecs_system 

CASE WHEN ebv.db_no IN (22978, 23218, 23219) THEN 'WECS 9500' 
 ELSE 'WECS 9520' 
END as wecs_system