雪花加入性能改进

Question

我需要在包含 1300 多列的表上创建一个视图。每个季度都会将新数据加载到表中（以百万为单位的行）。在创建视图时，我需要将其他表与基表连接起来。而且我还需要在视图中添加一个最近的行指示器。

CREATE OR REPLACE SECURE VIEW VIEW_NAME AS
SELECT lkp_tbl.col1,base_tbl.col1,base_tbl.col2,base_tbl.col3,........,base_tbl.col1334,1 as Is_Latest_Quarter FROM base_tbl full outer JOIN lkp_tbl
on base_tbl.CUST_ID = lkp_tbl.CUST_ID 
where snapshot_dt=(select max(snapshot_dt) from base_tbl)


union all


SELECT lkp_tbl.col1,base_tbl.col1,base_tbl.col2,base_tbl.col3,........,base_tbl.col1334,0 as Is_Latest_Quarter FROM base_tbl full outer JOIN lkp_tbl
on base_tbl.CUST_ID = lkp_tbl.CUST_ID 
where snapshot_dt!=(select max(snapshot_dt) from base_tbl);

创建此视图后，即使我们查询 100 行，查询的性能也太慢了。有没有一种方法可以让我们以更有效的方式创建视图。如果不是，我该如何提高性能？

Answer 1

只需使用一个 SELECT 语句并使用 CASE 语句计算 Is_Latest_Quarter

使用（几乎）实际 SQL 更新

CREATE OR REPLACE SECURE VIEW VIEW_NAME AS
SELECT {list of columns you want to include}
,CASE WHEN snapshot_dt=(select max(snapshot_dt) from base_tbl) THEN 1 
 ELSE 0 END as Is_Latest_Quarter
FROM base_tbl 
full outer JOIN lkp_tbl on base_tbl.CUST_ID = lkp_tbl.CUST_ID 

或者，如果 Snowflake 不喜欢该内联子查询，您可以使用类似以下的 CTE：

CREATE OR REPLACE SECURE VIEW VIEW_NAME AS
    WITH MAX_DATE AS (SELECT MAX(Ssnapshot_dt) AS max_snapshot_dt FROM base_tbl),
    SELECT {list of columns you want to include}
    ,CASE WHEN max_date.max_snapshot_dt is not null  THEN 1 
     ELSE 0 END as Is_Latest_Quarter
    FROM base_tbl 
    full outer JOIN lkp_tbl on base_tbl.CUST_ID = lkp_tbl.CUST_ID
    LEFT OUTER JOIN MAX_DATE ON base_tbl.snapshot_dt = max_date.max_snapshot_dt