如何在sql计算中使用变量

我有一张小桌子

[db2inst1@dashmpp-head-0 - Db2wh ~]$ db2 "select * from TEX"

C1                   C2        
-------------------- ----------
                1000 2000      

  1 record(s) selected.

我试着用case语句进行一个小的计算,如下所示:

SELECT c1,
CASE
    WHEN c1 > 0 THEN 10
    WHEN c1 = 30 THEN 5
    ELSE 1
END AS QuantityText,
c2,
100 / QuantityText as UTILIZATION
FROM TEX;

这是查询的语法是正确的,但当我运行它时,我得到:

SQL0206N  "QUANTITYTEXT" is not valid in the context where it is used.  
SQLSTATE=42703

如果不进行计算,以下查询运行良好:

[db2inst1@dashmpp-head-0 - Db2wh ~]$ db2 "SELECT c1,
> CASE
>     WHEN c1 > 0 THEN 'The quantity is greater than 30'
>     WHEN c1 = 30 THEN 'The quantity is 30'
>     ELSE 'The quantity is under 30'
> END AS QuantityText,
> c2
> FROM TEX;"

C1                   QUANTITYTEXT                    C2        
-------------------- ------------------------------- ----------
                1000 The quantity is greater than 30 2000      

  1 record(s) selected.

我是sql的新手,我不确定我在这里做错了什么。如何使用 QuantityText 在计算中?如果我对查询中的文本进行硬编码,它可以正常工作。

我尝试过的:

1. 已添加 100 / @QuantityText as UTILIZATION
2. 已添加 100 / bigint(double(QuantityText)) as CPU_UTILIZATION

    SELECT c1,
    c2,
    100 / QuantityText as UTILIZATION FROM (
    CASE
      WHEN c1 > 0 THEN 10
      WHEN c1 = 30 THEN 5
      ELSE 1
    END AS QuantityText,
    TEX);

SQL0104N  An unexpected token "CASE       WHEN" was found following 
"UTILIZATION FROM ( ".  Expected tokens may include:  "<select>".  
SQLSTATE=42601