Amazon redshift 红移优化

我正在寻找一些帮助，以优化以下。是否有一种方法可以用于消除每次调用sub select的需要，因为它们对于不同的字段几乎相同：

select 
       IdText AS EquipmentPointCode, 
       OnRLT AS Downtime,
       (   SELECT OnRLT FROM temp_pointsvr_uptime_dataset WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OnRLT > t1.OnRLT ORDER BY OnRLT ASC LIMIT 1) AS Uptime,
       (   SELECT LineDefault_Value1 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value1,
       (   SELECT LineDefault_Value2 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value2,
       (   SELECT LineDefault_Value3 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value3,
       (   SELECT LineDefault_Value4 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value4,
       (   SELECT LineDefault_Value5 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value5,
       (   SELECT LineDefault_Value6 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value6,
       (   SELECT LineDefault_Value7 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value7,
       (   SELECT StateDefault_Value1 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS StateDefault_Value1,
       (   SELECT StateDefault_Value2 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS StateDefault_Value2,
       (   SELECT StateDefault_Value3 FROM temp_not_pointsvr_downtime WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS StateDefault_Value3,
       'FM 10' AS Equipment
FROM temp_pointsvr_downtime t1
WHERE  IdText = (select IDtext from list_of_ids where rownum =1)     

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我觉得您试图做的事情可以通过case语句来完成，但是如果没有看到您正在使用的表/数据的示例，就很难确定

只要处理嵌套的select语句，您就应该能够使用一个公共表表达式一次性命中该表，而不是每次都从中重新选择：

WITH
 id_text_filter AS (
    SELECT IDtext
    FROM list_of_ids
    WHERE rownum = 1
) 

SELECT 
       IdText AS EquipmentPointCode, 
       OnRLT AS Downtime,
       (   SELECT OnRLT FROM temp_pointsvr_uptime_dataset WHERE IdText = (select IDtext from list_of_ids where rownum =1) AND OnRLT > t1.OnRLT ORDER BY OnRLT ASC LIMIT 1) AS Uptime,
       (   SELECT LineDefault_Value1 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value1,
       (   SELECT LineDefault_Value2 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value2,
       (   SELECT LineDefault_Value3 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value3,
       (   SELECT LineDefault_Value4 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value4,
       (   SELECT LineDefault_Value5 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value5,
       (   SELECT LineDefault_Value6 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value6,
       (   SELECT LineDefault_Value7 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS LineDefault_Value7,
       (   SELECT StateDefault_Value1 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS StateDefault_Value1,
       (   SELECT StateDefault_Value2 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS StateDefault_Value2,
       (   SELECT StateDefault_Value3 FROM temp_not_pointsvr_downtime WHERE ti.IdText = f.IDtext AND OffRLT = t1.OnRLT  ORDER BY ResetRLT DESC Limit 1) AS StateDefault_Value3,
       'FM 10' AS Equipment
FROM temp_pointsvr_downtime t1
JOIN id_text_filter f ON ti.IDtext = f.IDtext
WHERE  IdText = (SELECT IDtext FROM list_of_ids WHERE rownum =1)

同样，我不确定这段代码是否可以直接运行，因为我无法测试它。但想法应该是相似的：

1） 使用要用作筛选器的数据创建公共表表达式
2） 在主选择中加入该表

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3） 基于与公共表表达式的相等定义WHERE子句

天哪！你想用这句话达到什么目的？我怀疑您可以简单地使用联接，但很难理解您的查询。你能用一个简化的用例（例如没有那么多的子选项）重新写下你的问题，并描述你想要实现的目标吗？如果可能，显示表中的内容以及试图获得的输出。