SQL get ROW_NUMBER and COUNT on every SELECT request

问题

I´m building a grid mechanism where I need to retrieve data from Database the total or records found, retrieving just a range of these records with a row_number in it.

I´m using SqlServer for testing, but I need to support that on Oracle and MySql as well.

That´s what I´m trying, but I can´t make it work:

    SELECT * FROM 
           (SELECT ROW_NUMBER() AS RN, 
                   COUNT(*) AS TOTALCN, 
                   Id, 
                   Name, 
                   Phone 
            FROM MyTable WHERE Deleted='F')
            WHERE RN > 100 AND RN < 150;

The idea is:

MyTable -> number of records: 1000
Select Id, Name, Phone from MyTable where Deleted='F' -> number of records: 850
Get the records 100 to 150 from the 850.

I want to get a select like:

RN   TOTALCN Id    Name   Phone
1    850     Data  Data   Data
2    850     Data  Data   Data
3    850     Data  Data   Data
4    850     Data  Data   Data
5    850     Data  Data   Data
6    850     Data  Data   Data

The CN (850) will be my grid total number of records. The RN will be grid index for data.

CAn someone help me to accomplish that ?

Thanks for any help.

[EDIT]

So, I will defenetely add an ORDER BY on every SELECT. Here is what I´m getting so far:

SELECT * FROM (SELECT ROW_NUMBER() 
              OVER (ORDER BY ID)  AS RN, 
              COUNT(*) OVER (ORDER BY (SELECT NULL) AS CNT) 
              Id, Name Phone FROM MyTable WHERE Deleted='F') 
T WHERE RN > 100 AND RN < 500;

Am I going to the right way ?

How expensive will be that to SQL ?

回答1:

To include a COUNT(*) in the same SELECT clause with a bunch of detail rows is to fail. That's because COUNT(*) is an aggregate function. In the absence of GROUP BY it returns only one row in its result set. So, you need to query the count in its own SELECT statement.

SQL Server has the ROW_NUMBER() function. Oracle has the pseudocolumn named ROWNUM. And MySQL has a truly miserable hack for getting row numbers. It's described here. MySQL - Get row number on select

回答2:

This is probably meant to allow paginating. Showing the total number of rows can be really expensive.

One way that I've found to work well on a variety of databases is to split the work in two parts. First, you collect the ID of the relevant rows in a temporary table. Second, you query the full dataset. The data collected in the first part gives you an easy way to calculate the total number of rows and the IDs of rows on a certain page.

Here's a rough example for SQL Server. Note that the example does not rely on window functions like row_number(), which are not available in MySQL.

create table #id_list (rn int identity, pk int);

insert   #id_list
         (pk)
select   customer_id
from     customers
where    name like '%Joe%';

select   (select  count(*) from #id_list) as total_rows
,        rn -- The row's number
,        name
,        birth_date
,        ... -- Other columns
from     #id_list id
join     customer c
on       c.pk = c.customer_id
where    rn between 15 and 29; -- Second 15-row page

By the way, if feasible, I'd return this requirement to the designers to double check if this is worth spending a lot of time on. It is much simpler if you do not need to display the total number of rows.

来源：https://stackoverflow.com/questions/24940884/sql-get-row-number-and-count-on-every-select-request

标签

mysql

sql-server

oracle11g

aggregate-functions

row-number