SQL按周生成系列，如果没有找到，则返回0

Question

当一周内没有找到数据时，SQL将返回1.如何使它返回0？

SELECT w.week, COUNT(*) 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; 

Answer 1

你有外连接，因此更改count(*)到count(reviews.*)应该做的，试试：

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;