我们正在运行此查询:
SELECT concat_ws(' ', z.ticker,
CASE
WHEN a.date_approved IS NOT NULL THEN TO_CHAR(a.date_approved,'YYMMDD')
WHEN z.date_recommended IS NULL THEN '000000'
ELSE TO_CHAR(z.date_recommended,'YYMMDD')
END,
CASE
WHEN s.ticker IS NOT NULL THEN 6
WHEN a.approved_recommendation IS NOT NULL THEN approved_recommendation
ELSE current_recommendation
END,
REPLACE(CASE
WHEN comments IS NULL THEN 'N/C'
ELSE comments
END,' ','_'))
FROM recommendations z
LEFT JOIN (SELECT ticker FROM scr_tickers) s
ON z.ticker = s.ticker
LEFT JOIN (SELECT ticker, date_approved, approved_recommendation
FROM approved_recommendations) a
ON z.ticker = a.ticker
WHERE z.ticker NOT LIKE 'T.%'
AND z.ticker NOT LIKE 'V.%'
ORDER BY z.ticker;
现在,他们想在
comments
之后添加另一个数据项,即从 recommendations_history
表中检索最新的推荐值,其中推荐值 <>current_recommendation
。
为此,我可以执行
join
,将 ROW_NUMBER
与 ORDER BY
一起使用,然后选择第一行。这是在 PostgreSQL 中实现这一目标的最佳方法吗?
SELECT concat_ws(' ', z.ticker,
COALESCE(TO_CHAR(a.date_approved,'YYMMDD'),
TO_CHAR(z.date_recommended,'YYMMDD'),
'000000'),
CASE WHEN s.ticker IS NOT NULL THEN 6
ELSE COALESCE(a.approved_recommendation, current_recommendation)
END,
REPLACE(COALESCE(comments,'N/C'),' ','_'),
rh.recommendation_value)
FROM recommendations z
LEFT JOIN (SELECT ticker FROM scr_tickers) s
USING (ticker)
LEFT JOIN (SELECT ticker, date_approved, approved_recommendation
FROM approved_recommendations) a
USING (ticker)
LEFT JOIN (SELECT rh.ticker, rh.recommendation_value
FROM recommendations_history rh
WHERE z.current_recommendation<>rh.recommendation_value
LIMIT 1) rh
USING (ticker)
WHERE z.ticker NOT LIKE 'T.%'
AND z.ticker NOT LIKE 'V.%'
ORDER BY z.ticker;
case when x is null then y else x end
翻译为 coalesce(x,y)
to_char()
,则 null
函数将返回 null
join using
为您保存方程式并合并同名列尝试一下,我引入了
LEFT JOIN
来合并 recommendations_history
表中与建议表中当前建议不同的最新建议。这是通过加入使用 ROW_NUMBER()
窗口函数的子查询来实现的,该子查询按代码分区并按推荐日期降序排列。
SELECT concat_ws(' ',
z.ticker,
CASE
WHEN a.date_approved IS NOT NULL THEN TO_CHAR(a.date_approved,'YYMMDD')
WHEN z.date_recommended IS NULL THEN '000000'
ELSE TO_CHAR(z.date_recommended,'YYMMDD')
END,
CASE
WHEN s.ticker IS NOT NULL THEN 6
WHEN a.approved_recommendation IS NOT NULL THEN a.approved_recommendation
ELSE z.current_recommendation
END,
REPLACE(CASE
WHEN z.comments IS NULL THEN 'N/C'
ELSE z.comments
END, ' ', '_'),
COALESCE(rh.recommendation, 'No Recent Recommendation')
)
FROM recommendations z
LEFT JOIN (SELECT ticker FROM scr_tickers) s ON z.ticker = s.ticker
LEFT JOIN (SELECT ticker, date_approved, approved_recommendation
FROM approved_recommendations) a ON z.ticker = a.ticker
LEFT JOIN (SELECT ticker, recommendation, ROW_NUMBER() OVER (PARTITION BY ticker ORDER BY recommendation_date DESC) AS rn
FROM recommendations_history
WHERE recommendation <> (SELECT current_recommendation FROM recommendations WHERE ticker = recommendations_history.ticker)
) rh ON z.ticker = rh.ticker AND rh.rn = 1
WHERE z.ticker NOT LIKE 'T.%'
AND z.ticker NOT LIKE 'V.%'
ORDER BY z.ticker;