错误是您尝试act_month
在 JOIN 条件中引用输出列的名称 ( ),但它不可见 - 它尚未计算!尝试:
SELECT fta.liability_id
,fta.amount
,date_part('month', fta.act_date) AS act_month
FROM (
SELECT i
FROM generate_series(1,array_upper(ARRAY[1,2,3,4,5,6,7,8,9,10,11,12],1)) i
) ym
LEFT JOIN financial_t_account fta
ON ym.i = date_part('month', fta.act_date)::int;
您可以在很大程度上简化为:
SELECT fta.liability_id
,fta.amount
,date_part('month', fta.act_date) AS act_month
FROM generate_series(1,12) ym(i)
LEFT JOIN financial_t_account fta
ON ym.i = date_part('month', fta.act_date)::int;
或者,如果您想从数组中获取任意月份,请使用unnest()
而不是generate_series()
:
...
FROM unnest(ARRAY[1,2,4,57,8,11,12]) ym(i)
...
使用CTE(或子查询)来避免重复表达式(并计算两次):
WITH x AS (
SELECT *, date_part('month', act_date)::int As act_month
FROM financial_t_account
)
SELECT x.liability_id
,x.amount
,x.act_month
FROM generate_series(1,12) ym(i)
LEFT JOIN x ON ym.i = x.act_month;