鉴于此表:
SELECT * FROM CommodityPricing order by dateField
"SILVER";60.45;"2002-01-01"
"GOLD";130.45;"2002-01-01"
"COPPER";96.45;"2002-01-01"
"SILVER";70.45;"2003-01-01"
"GOLD";140.45;"2003-01-01"
"COPPER";99.45;"2003-01-01"
"GOLD";150.45;"2004-01-01"
"MERCURY";60;"2004-01-01"
"SILVER";80.45;"2004-01-01"
截至2004年,COPPER被淘汰并引入了汞
如何为(array_agg(value order by date desc) ) [1]
获取NULL
COPPER
的值?
select commodity,(array_agg(value order by date desc) ) --[1]
from CommodityPricing
group by commodity
"COPPER";"{99.45,96.45}"
"GOLD";"{150.45,140.45,130.45}"
"MERCURY";"{60}"
"SILVER";"{80.45,70.45,60.45}"
答案 0 :(得分:0)
select
commodity,
array_agg(
case when commodity = 'COPPER' then null else price end
order by date desc
)
from CommodityPricing
group by commodity
;
答案 1 :(得分:0)
To" pad"在结果数组中缺少具有NULL值的行,在完整的行网格和 LEFT JOIN
实际值的网格上构建查询。
鉴于此表定义:
CREATE TEMP TABLE price (
commodity text
, value numeric
, ts timestamp -- using ts instead of the inappropriate name date
);
我使用generate_series()
获取表示年份的时间戳列表,并CROSS JOIN
列出所有商品的唯一列表(SELECT DISTINCT ...
)。
SELECT commodity, (array_agg(value ORDER BY ts DESC)) AS years
FROM generate_series ('2002-01-01 00:00:00'::timestamp
, '2004-01-01 00:00:00'::timestamp
, '1y') t(ts)
CROSS JOIN (SELECT DISTINCT commodity FROM price) c(commodity)
LEFT JOIN price p USING (ts, commodity)
GROUP BY commodity;
结果:
COPPER {NULL,99.45,96.45}
GOLD {150.45,140.45,130.45}
MERCURY {60,NULL,NULL}
SILVER {80.45,70.45,60.45}
SQL Fiddle.
我将数组转换为小提琴中的文本,因为显示很糟糕,否则会吞下NULL值。