如何在SQL中实现tidyr的complete（）？

Question

使用虚拟示例，我需要完成具有隐式缺失值的数据集。使用R的函数tidyr在complete中这是微不足道的。

library(tidyr)

df <- data.frame(Borough = c('Brooklyn', 'Brooklyn', 'Queens'),
                 Crime = c('Robbery', 'Homicide', 'Drug'),
                 Count=c(1, 2, 1))

> df
   Borough    Crime Count
1 Brooklyn  Robbery     1
2 Brooklyn Homicide     2
3   Queens     Drug     1

#Complete implicit missing values

> complete(df, Borough, Crime, fill=list(Count=0))
   Borough    Crime Count
1 Brooklyn     Drug     0
2 Brooklyn Homicide     2
3 Brooklyn  Robbery     1
4   Queens     Drug     1
5   Queens Homicide     0
6   Queens  Robbery     0

但是，如果真实数据非常大并且存储在Oracle的SQL表中，那么如何使用SQL查询来完成呢？

Answer 1

将不同的行政区域与犯罪行交叉加入，并将原始表格连接起来，以获取0行的缺失行。

select b.borough,c.crime,coalesce(t.count,0) as count
from (select distinct borough from tbl) b
cross join (select distinct crime from tbl) c
left join tbl t on t.borough=b.borough and t.crime=c.crime