Shulou(Shulou.com)06/01 Report--

In this issue, the editor will bring you a number of records about how SQL returns the maximum value. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

It is not difficult to get the first piece of data through the top or limit clause in SQL, and with sorting, you can get the largest row:

Select top 1 * from T order by f desc

If the maximum has multiple records, if you want to get all of them, you need the subquery to get the maximum, and then traverse the data twice to get all the records that are the same as the maximum:

Select * from T where f = (select max (f) from T)

Or use the window function rank () to do the ranking, and then take the first place:

Select * from (select T. rank () over (partition by 1 order by age desc) f_rank from T) where f_rank=1

In any case, it has to be divided into two steps to get the result. Imagine that we go to the seaside to pick up the largest shells and compare them while walking. It is natural to keep the largest shells and keep the same big ones in our hands. However, the expression ability of SQL is limited, and it does not retain multiple maximum capabilities, so it can only go back and forth twice. If this kind of problem-solving idea is nested in several layers, it will bring a great burden of understanding to programmers.

In this case, it is easier to use the aggregator SPL language to get the raw data from the database:

> T=connect ("mysqlDB") .query ("select * from T")

Then use the @ an option of maxp to take out all the maximum records:

= T.maxp@a (f)

The above usage is a small improvement, and there are more awkward and roundabout calculations in SQL. The root cause is that the relational algebra system on which SQL depends does not support ordered set computation, cannot make use of the position of data in the set, and does not balance the relationship between set and discrete data.

The above are the multiple records of how the SQL returned the maximum value shared by the editor. If you happen to have similar doubts, please refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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