Sql 用查询过滤的Postgres

我目前有以下疑问：

WITH instances AS (
    SELECT b.ldtc as date, a.fk_item_id, b.movement, a.quantity, 
        CASE WHEN b.movement = 'Inbound' THEN a.quantity ELSE -a.quantity END as absquantity
    FROM inventory_resupplylogiteminstance a
    INNER JOIN inventory_resupplylog b ON b.uid = a.fk_resupply_log_id
)

SELECT a.name, 
    SUM(CASE WHEN b.date < ('2018-10-10'::date) THEN b.absquantity END) as starting_balance,

    SUM(CASE WHEN b.date > ('2018-10-10'::date) AND b.date < ('2018-10-12'::date) AND b.movement = 'aa' THEN b.absquantity END) as aa,
    SUM(CASE WHEN b.date > ('2018-10-10'::date) AND b.date < ('2018-10-12'::date) AND b.movement = 'bb' THEN b.absquantity END) as bb,
    SUM(CASE WHEN b.date > ('2018-10-10'::date) AND b.date < ('2018-10-12'::date) AND b.movement = 'cc' THEN b.absquantity END) as cc,
    SUM(CASE WHEN b.date > ('2018-10-10'::date) AND b.date < ('2018-10-12'::date) AND b.movement = 'dd' THEN b.absquantity END) as dd,

    SUM(CASE WHEN b.date < ('2018-10-12'::date) THEN b.absquantity END) AS ending_balance




FROM inventory_item a
LEFT JOIN instances b ON b.fk_item_id = a.uid

GROUP BY a.uid, a.name
ORDER BY a.name

---

如您所见，第二行到第五行的总和是多余的，因为它们在查询b.date在2018-10-10和2018-10-12之间的行。有没有办法重写我的查询，只需写一次b.date>'2018-10-10'：：date和b.date<'2018-10-12'：：date，就可以在同一行上选择起始余额和结束余额？

您可以检查CTE中的范围，并创建一个标志，指示该行是否在指定范围内

然后，您可以在最终选择中使用该标志。切换到筛选器表达式也会使其更具可读性：

WITH instances AS (
  SELECT b.ldtc as date, 
         a.fk_item_id, 
         b.movement, 
         a.quantity, 
         CASE 
           WHEN b.movement = 'Inbound' THEN a.quantity 
           ELSE -a.quantity 
         END as absquantity,
         -- the column in_range returns either true or false
         (b.ldtc > ('2018-10-10'::date) AND b.date < ('2018-10-12'::date)) as in_range
  FROM inventory_resupplylogiteminstance a
    INNER JOIN inventory_resupplylog b ON b.uid = a.fk_resupply_log_id
)
SELECT a.name, 
       SUM(b.absquantity) filter (where b.date < '2018-10-10'::date) as starting_balance,
       SUM(b.absquantity) filter (where in_range and b.movement = 'aa') as aa,
       SUM(b.absquantity) filter (where in_range and b.movement = 'bb') as bb,
       SUM(b.absquantity) filter (where in_range and b.movement = 'cc') as cc,
       SUM(b.absquantity) filter (where in_range and b.movement = 'dd') as dd,
       SUM(b.absquantity) filter (where b.date < '2018-10-12'::date) AS ending_balance
FROM inventory_item a
  LEFT JOIN instances b ON b.fk_item_id = a.uid
GROUP BY a.uid, a.name
ORDER BY a.name;

如果您也不想重复开始和结束余额的日期，可以将要测试的范围放入CTE，然后在最终查询中使用Postgres：

WITH instances AS (
  SELECT b.ldtc as date, 
         a.fk_item_id, 
         b.movement, 
         a.quantity, 
         CASE 
           WHEN b.movement = 'Inbound' THEN a.quantity 
           ELSE -a.quantity 
         END as absquantity,
         daterange('2018-10-10'::date, '2018-10-12'::date, '()') as check_range
  FROM inventory_resupplylogiteminstance a
    INNER JOIN inventory_resupplylog b ON b.uid = a.fk_resupply_log_id
)
SELECT a.name, 
    SUM(b.absquantity) filter (where b.date < lower(check_range)) as starting_balance,
    SUM(b.absquantity) filter (where b.date <@ b.check_range and b.movement = 'aa') as aa,
    SUM(b.absquantity) filter (where b.date <@ b.check_range and b.movement = 'bb') as bb,
    SUM(b.absquantity) filter (where b.date <@ b.check_range and b.movement = 'cc') as cc,
    SUM(b.absquantity) filter (where b.date <@ b.check_range and b.movement = 'dd') as dd,
    SUM(b.absquantity) filter (where b.date < upper(b.check_range))) AS ending_balance
FROM inventory_item a
  LEFT JOIN instances b ON b.fk_item_id = a.uid
GROUP BY a.uid, a.name
ORDER BY a.name;

daterange'2018-10-10'：：日期，'2018-10-12'：：日期，创建一个不包括这两个日期的日期

---

哇，谢谢一匹没有名字的马，这太干净了！肯定比我想到的要好得多。问题是，我注意到，当b.date<'2018-10-10'：date然后b.absquantity结束为起始\ U余额时，您用SUMb.absquantity过滤器替换了SUMCASE，其中b.date

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