Oracle 表中的随机行
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Oracle random row from table
提问by Adrian
I found this solution for selecting a random row from a table in Oracle. Actually sorting rows in a random manner, but you can fetch only the first row for a random result.
我找到了这个解决方案，用于从 Oracle 的表中选择随机行。实际上以随机方式对行进行排序，但您只能获取随机结果的第一行。
SELECT *
FROM table
ORDER BY dbms_random.value;
I just don't understand how it works. After ORDER BY it should be a column used for sorting. I see that "dbms_random.value" returns a value lower than zero. This behavior can be explained or is just like that?
我只是不明白它是如何工作的。ORDER BY 之后应该是用于排序的列。我看到“dbms_random.value”返回一个小于零的值。这种行为可以解释还是就是这样？
Thanks
谢谢
回答by Kevin Burton
you could also think of it like this:
你也可以这样想：
SELECT col1, col2, dbms_random.value
FROM table
ORDER BY 3
In this example the number 3 = the third column
在本例中，数字 3 = 第三列
回答by Aitor
When you order by dbms_random.value, Oracle orders by the expression, not for a column.For every record Oracle calculate a random number, and then order by this number.
当你按dbms_random.value 排序时，Oracle 按表达式排序，而不是针对一个列。Oracle 为每条记录计算一个随机数，然后按这个数字排序。
In a similar way, is like this:
以类似的方式，是这样的：
select * from emp order by upper(ename);
You have an order by based on a function.
您有一个基于函数的 order by。
