关于永不结束的PostgreSQL查询

我遇到查询问题，下面在PostgreSQL中运行但是永不结束。你有什么建议吗？关于永不结束的PostgreSQL查询

WITH tmp1 AS (
    SELECT istante, produzione, 
     CAST (CAST (produzione AS FLOAT)/12000 AS NUMERIC(6,2)) AS proden, 
     CAST (CAST (consumo AS FLOAT)/12000 AS NUMERIC(6,2)) AS consen 
    FROM ftv1 
), tmp2 AS (
    SELECT LEAST(proden, consen) AS aconsen 
    FROM tmp1 
) 
SELECT tmp1.istante, tmp1.proden, tmp1.consen, 
     (tmp1.consen - tmp2.aconsen) AS enconsen 
FROM tmp1, tmp2;

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2017-08-10 Nicola Mingotti

你的表有多少行，你在等待多久？*永不结束*？ – yanman1234

选择FROM tmp1，tmp2语句作为笛卡尔连接。因为它没有完成。请给出正确的连接条件 –

没有任何定义“ftv1”和“tmp2”的连接条件的WHERE子句，所以实际上它是一个交叉连接，它将第一个表中的所有行与第二个表中的所有行进行组合。如果第一个表包含例如10.000行，第二个表包含20.000行，那么交叉连接产生10000 x 20000 = 200000000行 - 它需要一些时间（可能需要十几天，甚至几个星期，但最有可能直到磁盘空间耗尽，因为RDBMS将所有生成的行保存在临时表中的磁盘上）。 – krokodilko

尝试类似下面

WITH tmp1 AS (
    SELECT istante, produzione, 
     CAST (CAST (produzione AS FLOAT)/12000 AS NUMERIC(6,2)) AS proden, 
     CAST (CAST (consumo AS FLOAT)/12000 AS NUMERIC(6,2)) AS consen 
    FROM ftv1 
), tmp2 AS (
    SELECT istante,LEAST(proden, consen) AS aconsen 
    FROM tmp1 
) 
SELECT t1.istante, t1.proden, t1.consen, 
     (t1.consen - t2.aconsen) AS enconsen 
FROM tmp1 t1 
join tmp2 t2 
on t1.istante = t2.istante;

来源

2017-08-10 13:53:12

感谢您的回答，您的查询在大约8分钟内完成（在一个小小的Debian虚拟机中）。我刚刚发布的发布大约需要3-4分钟。 –

看到你的答案我用下面的代码解决之前，反正现在我知道为什么这个工程，没有笛卡尔乘积。谢谢大家的帮助。

WITH tmp1 AS (
    SELECT istante, produzione, 
     (CAST (produzione AS FLOAT)/12000) AS proden, 
     (CAST (consumo AS FLOAT)/12000) AS consen 
    FROM ftv1 
), tmp2 AS (
    SELECT istante, produzione, proden, consen, 
     LEAST(proden, consen) AS aconsen 
    FROM tmp1 
) 
SELECT istante, proden, consen, aconsen, 
     (consen - aconsen) AS enconsen, 
     GREATEST(proden - consen, 0) as senten 
FROM tmp2;

来源

2017-08-10 17:30:42

关于永不结束的PostgreSQL查询

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