如何基于Snowflake中的表达式定义集群键？

Question

根据Snowflake文档（https://docs.snowflake.net/manuals/user-guide/tables-clustering-keys.html），群集键可以定义为一个或多个表列/表达式。他们带来的示例是：

-- cluster by expressions
create or replace table t2 (c1 timestamp, c2 string, c3 number) cluster by (to_date(c1), substring(c2, 0, 10));

我想从日期列中提取年，月和日，并基于这些表达式创建集群键，但没有找到解决方法。这是我已经尝试过的：

 CREATE TABLE TBL_DATECREATED  (DATECREATED_UTC)  
 CLUSTER BY (
              TO_DATE(DATECREATED_UTC)
              )  
 AS
 SELECT DATECREATED_UTC FROM BASETABLE_CONTACTS

结果：

 SQL compilation error: invalid type [TO_DATE(TBL_DATECREATED.DATECREATED_UTC)] for parameter 'TO_DATE'

---

**内容：SELECT TO_DATE(DATECREATED_UTC) FROM BASETABLE_CONTACTS正常！

CREATE MATERIALIZED VIEW MV_DATECREATED (DATECREATED_UTC, EMAILADDRESS)
CLUSTER BY ( year(DATECREATED_UTC)
             -- extract(year from DATECREATED_UTC)
             ,EMAILADDRESS
            )
AS
SELECT DATECREATED_UTC, EMAILADDRESS FROM BASETABLE_CONTACTS 

结果：

SQL compilation error: Function EXTRACT does not support UNKNOWN argument type
(for commented expression i received the same error message)

---

CREATE MATERIALIZED VIEW MV_DATECREATED (DATECREATED_UTC, EMAILADDRESS)
CLUSTER BY (  DATECREATED_UTC
             ,substring(EMAILADDRESS, 1, 3)
            )
AS
SELECT DATECREATED_UTC, EMAILADDRESS FROM BASETABLE_CONTACTS 

结果：

SQL compilation error: error line 3 at position 14 Invalid argument types for function 'SUBSTRING': (UNKNOWN, NUMBER(1,0), NUMBER(1,0))

感谢您的每个建议/解决方案！

Answer 1

尝试以下操作，当您在创建表的同时定义聚类键时，Snowflake可能无法正确确定列的数据类型？

CREATE MATERIALIZED VIEW MV_DATECREATED (DATECREATED_UTC timestamp, EMAILADDRESS varchar)
CLUSTER BY ( year(DATECREATED_UTC)
             -- extract(year from DATECREATED_UTC)
             ,EMAILADDRESS
            )
AS
SELECT DATECREATED_UTC, EMAILADDRESS FROM BASETABLE_CONTACTS 

Answer 2

对于第一个错误，请尝试将数据类型添加到创建表中。例如：

CREATE TABLE TBL_DATECREATED  (DATECREATED_UTC timestamptz)

对于第二和第三期，请检查数据类型是否符合您的期望。