一、model 空值

model 子句存在空值的原因有兩個
1、單員格存在，但值為空
2、單元格不存在

1、例項演示 nav

select product,
       country,
       year,
       week,
       sale      
  from sales_fact
 where country = 'Australia'
   and product = 'Xtend Memory'
  model keep nav return updated rows
--keep   nav是預設值 nav(non avaliable values
 
) 沒有可用值
  partition by(product, country)
  dimension by(year, week) 
  measures(sale) 
  rules sequential order(sale [ 2001, 1 ]
 order by year, week = sale [ 2001, 1 ], sale [ 2002, 1 ]
 order by year, week = sale [ 2001, 1 ] + sale [ 2002, 1 ])
 order by product, country, year, week

2、例項演示 ignore nav

select
 
 product,
       country,
       year,
       week,
       sale      
  from sales_fact
 where country = 'Australia'
   and product = 'Xtend Memory'
  model ignore nav return updated rows 
-- 如果位空 則返回0
  partition by(product, country)
  dimension by(year, week) 
  measures(sale) 
  rules sequential order
 
(sale [ 2001, 1 ]
 order by year, week = sale [ 2001, 1 ], sale [ 2002, 1 ]
 order by year, week = sale [ 2001, 1 ] + sale [ 2002, 1 ])
 order by product, country, year, week

可以回憶上一篇 https://blog.csdn.net/whandgdh/article/details/82697327 中presetv 以及presentnnv 兩個函式對空值的處理

二、model子句效能調優

model 子句最關鍵的就是規則求解。
規則求解可以使用如下5種演算法：
1、ACYCLIC
2、ACYCLIC FAST
3、CYCLIC
4、ORDERED
5、ORDERED FAST
ACYCLIC FAST ORDERED FAST是相對較優的演算法，允許單元格高效求解。
如果演算法指定了automatic order 會選擇使用ACYCLIC和CYCLIC 演算法
如果指定了 sequential order 則會選擇使用ORDERED 演算法
如果規則訪問某個獨立的單元格不進行聚合有可能選擇 ACYCLIC FAST 或ORDERED FAST

2、執行計劃

2、1 ACYCLIC
例項演示 ：model 子句開始求庫存的例項 我們在規則種再加上order

select product, country, year, week, inventory, sale, receipts
  from sales_fact
 where country = 'Australia'
   and product = 'Xtend Memory' 
   model return updated rows 
   partition by(product, country)
   dimension by(year, week)
   measures(0 inventory, sale, receipts) 
   rules automatic
   order(inventory [ year, week ] order by year ,week
-- order 來控制規則之間的依賴關係，避免迴圈依賴性
= nvl(inventory [ cv(year), cv(week) - 1 ], 0) - sale [ cv(year), cv(week) ] + receipts [ cv(year), cv(week) ])
 order by product, country, year, week;

ACYCLIC 表明了規則之間沒有可能的CYCLIC（迴圈）依賴關係
2.2、ACYCLIC FAST
如果規則只訪問一個單元格，可以使用ACYCLIC FAST 演算法

select product, country, year, week,   sale ,sale_modify
  from sales_fact
 where country = 'Australia'
   and product = 'Xtend Memory' 
   model return updated rows 
   partition by(product, country)
   dimension by(year, week)
   measures( 0 sale_modify, sale ) 
   rules automatic
   order(sale_modify[2001,1]=sale[2001,1]*10)
 order by product, country, year, week;

2.3 、CYCLIC

select product, country, year, week, inventory, sale, receipts
  from sales_fact
 where country = 'Australia'
   and product = 'Xtend Memory' 
   model return updated rows 
   partition by(product, country)
   dimension by(year, week)
   measures(0 inventory, sale, receipts) 
   rules automatic
   order(inventory [ year, week ] = nvl(inventory [ cv(year), cv(week) - 1 ], 0) - sale [ cv(year), cv(week) ] + receipts [ cv(year), cv(week) ])
 order by product, country, year, week;

2.4、ORDERED

 select product, country, year, week, inventory, sale, receipts,sale_modify
  from sales_fact
 where country = 'Australia'
   and product = 'Xtend Memory' 
   model return updated rows 
   partition by(product, country)
   dimension by(year, week)
   measures(0 inventory,0 sale_modify,sale, receipts) 
   rules sequential
   order(inventory [ year, week ] order by year ,week
-- order 來控制規則之間的依賴關係，避免迴圈依賴性
= nvl(inventory [ cv(year), cv(week) - 1 ], 0) - sale [ cv(year), cv(week) ] + receipts [ cv(year), cv(week) ],
sale_modify[2001,1]=sale[2001,1]*10
)
 order by product, country, year, week;