有没有办法在 Snowflake/SQL 中简写这个 CASE 语句？

Question

在这里有这个案例陈述，我想与“CASE WHEN”和“CASE ILIKE”一起使用，类似于以下内容：

SELECT
  CASE coalesce(lower(regexp_substr(random_sample_column, '\/key_word\/\\d+\/([\\w-]+)(\/|$)', 1, 1, 'e', 1)), random_sample_column)
     when 'green' then 'GO'
     when 'red' then 'STOP'
     when 'yellow' then 'SLOW'
     else
         case when coalesce(lower(regexp_substr(random_sample_column, '\/key_word\/\\d+\/([\\w-]+) ilike '%green' then 'GO?'
         case when coalesce(lower(regexp_substr(random_sample_column, '\/key_word\/\\d+\/([\\w-]+) ilike '%yellow' then 'SLOW?'
         case when coalesce(lower(regexp_substr(random_sample_column, '\/key_word\/\\d+\/([\\w-]+) ilike '%red' then 'STOP?'     
   END as sample_derived_column
FROM SAMPLE_TABLE_NAME;

有没有一种方法可以编写类似于代码块顶部“CASE WHEN”语句中使用的“速记”的（NESTED）类似案例语句？

提前致谢！

样本数据在这里：

random_sample_column
--------------
yellow30-1123$%schmidt
jingle43123heimer
red
isthelightgreen
beluw
beow
blue

Answer 1

一种可能的方法是使用列别名：

WITH cte AS (
SELECT *,
  coalesce(lower(regexp_substr(random_sample_column, '/key_word/\d+/([\w-]+)(/|$)', 1, 1, 'e', 1)), random_sample_column) AS helper_col1,
  coalesce(lower(regexp_substr(random_sample_column, '/key_word/\d+/([\w-]+') AS helper_col2,
  CASE helper_col1
     when 'green' then 'GO'
     when 'red' then 'STOP'
     when 'yellow' then 'SLOW'
     else
         case when helper_col2 ilike '%green' then 'GO?'
              when helper_col2 ilike '%yellow' then 'SLOW?'
              when helper_col2 ilike '%red' then 'STOP?' 
         end    
   END as sample_derived_column
FROM SAMPLE_TABLE_NAME
)
SELECT * EXCLUDE (helper_col1, helper_col2)
FROM cte;

---

嵌套不可读，所以：

WITH cte AS (
SELECT *,
  coalesce(lower(regexp_substr(random_sample_column, '/key_word/\d+/([\w-]+)(/|$)', 1, 1, 'e', 1)), random_sample_column) AS helper_col1,
  coalesce(lower(regexp_substr(random_sample_column, '/key_word/\d+/([\w-]+') AS helper_col2,
  CASE
     when helper_col1 =  'green'      then 'GO'
     when helper_col1 = 'red'         then 'STOP'
     when helper_col1 = 'yellow'      then 'SLOW'
     when helper_col2 ilike '%green'  then 'GO?'
     when helper_col2 ilike '%yellow' then 'SLOW?'
     when helper_col2 ilike '%red'    then 'STOP?'       
   END as sample_derived_column
FROM SAMPLE_TABLE_NAME
)
SELECT * EXCLUDE (helper_col1, helper_col2)
FROM cte;

---

编辑：

为了使用 LIKE 谓词和通配符执行简单的 case 表达式：

SELECT 
   CASE expresssion
     WHEN ILIKE '%green' THEN 'GO?'
     WHEN ILIKE '%yellow' THEN 'SLOW?'
     WHEN ILIKE '%red' THEN 'STOP?'
   END 
FROM SAMPLE_TABLE_NAME;

使用的 SQL 方言必须实现可选的 SQL:2003 Extended CASE expression(F262) 特性。

更多信息：SQL 'CASE WHEN x' vs. 'CASE x WHEN' with greater-than condition?