如果没有找到，SQL按周生成系列返回0

Question

如果一周内没有找到数据，SQL将返回1.如何让它返回0？

grp <- with(df, cummax(match(StudentAndClass, LETTERS[1:3], nomatch = 0)))
do.call(rbind, lapply(split(df, grp), function(x) 
     data.frame(Class = x[,1][2:(nrow(x)-1)], Student = x[[1]][1], stringsAsFactors=FALSE)))

Answer 1

您有外部联接，因此将count(*)更改为count(reviews.*)应该这样做，请尝试：

SELECT w.week, COUNT(reviews.*) AS total
FROM (SELECT generate_series(min(DATE_TRUNC('week', created_at)),
                             max(DATE_TRUNC('week', created_at)),
                             interval '7 day'
                            ) as week
      FROM reviews
     ) w LEFT JOIN
     "reviews" 
     ON DATE_TRUNC('week', created_at) = w.week
GROUP BY w.week
ORDER BY w.week;