Questions about random queries

w220913

Such as the title: I want to randomly select a record from a table A, I used two methods, but the results obtained are completely different, please ask prawns:


method one:
select * from tableA where rownum <2 order by dbms_random.random;

Method Two:
select * from (select * from tableA order by dbms_random.random) where rownum <2;


Method one filters out the same record every time
Method two filter out different records each time

Why is the first method not working? According to reason, both methods are random sorting first, and then filtering. Why doesn't the first method work?

我是杀人狂

You can use this sentence:
select top 1 * from tableA order by newid()

tran123

The first method is to select a record from the records, and then randomly sort this record
Method two is to randomly select all records, and then select the first one

select ... where ... order by First select the records that meet the conditions, and then sort the records. Isn't that the case?

terrorlin

tran123

correct

nature

The first floor is the wording of SQLSERVER