多个 case 语句/多个 Update 语句答案

【问题标题】：Multiple case statements/Multiple Update statement多个 case 语句/多个 Update 语句
【发布时间】：2019-07-25 13:36:25
【问题描述】：

你能告诉我如何在同一列上使用 CASE 语句吗？

update FRIDAY.Joined_table
SET
Cost = CASE WHEN Channel = 'SEA' THEN Paid_Costs ELSE Cost END,
Clicks = CASE WHEN Channel = 'SEA' THEN Paid_Clicks ELSE Clicks END,
impressions = CASE WHEN Channel = 'SEA' THEN Paid_Impressions ELSE Impressions END,
Cost = CASE WHEN Channel = 'Performance-Display' THEN DBM_Costs ELSE cost END
Where New_Ids IS NOT NULL

“这里告诉我：在 [6:1] 多次更新分配的项目成本

【问题讨论】：

标签： mysql google-bigquery

【解决方案1】：

你可以试试下面-

update FRIDAY.Joined_table
SET
Cost = CASE WHEN Channel = 'SEA' THEN Paid_Costs 
WHEN Channel = 'Performance-Display' THEN DBM_Costs ELSE Cost END,
Clicks = CASE WHEN Channel = 'SEA' THEN Paid_Clicks ELSE Clicks END,
impressions = CASE WHEN Channel = 'SEA' THEN Paid_Impressions ELSE Impressions END
Where New_Ids IS NOT NULL

【讨论】：

【解决方案2】：

对于 BigQuery 标准 SQL

下面是一个替代选项，它消除了表达 CASE 语句时的冗余，看起来更简洁，更易于管理

#standardSQL
UPDATE FRIDAY.Joined_table t1
SET 
  cost = x, 
  clicks = y, 
  impressions = z
FROM FRIDAY.Joined_table t2,
UNNEST([
  CASE channel 
    WHEN 'SEA' THEN STRUCT(paid_costs AS x, paid_clicks AS y, paid_impressions AS z)
    WHEN 'Performance-Display' THEN STRUCT(dbm_costs AS x, clicks AS y, impressions AS z)
    ELSE STRUCT(cost AS x, clicks AS y, impressions AS z)
  END 
  ]) val
WHERE TO_JSON_STRING(t1) = TO_JSON_STRING(t2)

没有什么是零价格的——所以，这里有自我加入：o(

为了解决这个问题 - 下面是另一种选择

#standardSQL
CREATE TEMP FUNCTION CASE_UPDATE(t ANY TYPE) AS (
  CASE t.channel 
    WHEN 'SEA' THEN STRUCT(t.paid_costs AS x, t.paid_clicks AS y, t.paid_impressions AS z)
    WHEN 'Performance-Display' THEN STRUCT(t.dbm_costs AS x, t.clicks AS y, t.impressions AS z)
    ELSE STRUCT(t.cost AS x, t.clicks AS y, t.impressions AS z)
  END  
);
UPDATE FRIDAY.Joined_table t 
SET 
  cost = CASE_UPDATE(t).x, 
  clicks = CASE_UPDATE(t).y, 
  impressions = CASE_UPDATE(t).z
WHERE TRUE

为了进一步简化，上面最终可以写成（假设你知道更新列使用什么类型，比如 INT64，或者 FLOAT64 / NUMERIC 等）

#standardSQL
CREATE TEMP FUNCTION CASE_UPDATE(t ANY TYPE) 
RETURNS STRUCT<cost FLOAT64, clicks INT64, impressions INT64>
AS (
  CASE t.channel 
    WHEN 'SEA' THEN STRUCT(t.paid_costs, t.paid_clicks, t.paid_impressions)
    WHEN 'Performance-Display' THEN STRUCT(t.dbm_costs, t.clicks, t.impressions)
    ELSE STRUCT(t.cost, t.clicks, t.impressions)
  END  
);
UPDATE FRIDAY.Joined_table t
SET 
  cost = CASE_UPDATE(t).cost, 
  clicks = CASE_UPDATE(t).clicks, 
  impressions = CASE_UPDATE(t).impressions
WHERE TRUE

【讨论】：