I'm using SQL server 2014,I'm fetching data from a view.The order of items is getting changed once i use Group by ,how can i get the order back after using this Group by,There is one date column,but its not saving any time,So i can't sort it based on date also..
How can I display the data in the same order as it displayed before using Group by?Anyone have any idea please help?
Thanks
Tables and views are essentially unordered sets. To get rows in a specific order, you should always add an ORDER BY clause on the columns you wish to order on.
I'm assuming you previously selected from the VIEW without an ORDER BY clause. The order in which rows are returned from a SELECT statement without an ORDER BY statement is undefined. The order you are getting them in, can change due to any number of reasons (eg some are listed here).
Your problem stems from the mistake you made on relying on the order from a SELECT from a VIEW without an ORDER BY. You should have had an ORDER BY clause in your SELECT statement to begin with.
How can I display the data in the same order as it displayed before using Group by?
The answer: You can't if your initial statement did not have an ORDER BY clause.
The resolution: Determine the order you want the resultset in and add an ORDER BY clause on those columns, both in your initial query and the version with the GROUP BY clause.
Maybe you can use the row_number() function without any OVER and ORDER BY keywords? This should be done in a sub-select and when you group the data in the outer SELECT, use the AVG() function on the numbered column and ORDER the result by this. The problem is, that when you group rows, the original rows disappear. That's kind if the purpose of GROUP BY. ;) Depending on what you GROUP BY, what you're asking might be logically impossible.
EDIT:
Found this solution Googling: http://blog.sqlauthority.com/2015/05/05/sql-server-generating-row-number-without-ordering-any-columns/
So you can number rows like this to maintain the order of rows from the table before you GROUP BY:
row_number() OVER (ORDER BY (SELECT 1))
The only way you can enforce a specific order is to explicitly use a ORDER BY clause. Otherwise the order of rows is not guaranteed (take a look at this article for more details) and the database engine will return the rows based on "as fast as it can" or "as fast as it can retrieve them from disk" rule. So, order can also vary between executions of the same query in the span of a few seconds.
When doing a DISTINCT, GROUP BY or ORDER BY, SQL Server automatically does a SORT of the data based on an index it uses for that query.
Looking at the execution plan of your query will show you what index (and implicitly columns in that index) is being used to sort the data.
Related
enter image description here I am learning how to order by is used in SQL query, then I learned that order by and distinctly don't work together but, when I try to do it practically it worked. I am so confused even after asking chatgpt what the relationship is between order by and distinct.
I learned that when executing SQL queries, the ORDER BY clause comes after the SELECT clause. This means that the database will first retrieve the data specified in the SELECT clause, and then sort it based on the criteria specified in the ORDER BY clause. If the column used in the ORDER BY clause is not present in the SELECT clause, the database will automatically include that column in the select and do order by on both the columns and give result column only column given in SELECT.
However, when using both DISTINCT and ORDER BY together, the outcome may not be what is expected. This is because DISTINCT acts on both the columns in the SELECT clause and the column in the ORDER BY clause. This may cause unexpected results, especially in MySQL.
I found that when I tried this in practice, it still produced the desired results, which makes me question if I learned something incorrectly or if there is missing information that I am unaware of.
I am using the MYSQL database.
It seems there are some spaces before your unique value. It will be appropriate to perform TRIM/RTRIM and remove these spaces in the DISTINC clause itself.
It should be something like this:
DISTINCT TRIM(value) AS trim_value
...
ORDER BY trim_value
Also, it is possible that these are not spaces but some other characters which need to be replace, too.
It seems if I add ROW_NUMBER in a simple select query, the results are sorted automatically by the ROW_NUMBER column even without order by added to the select query at the end. I tried this on
without ROW_NUMBER - results are in random order
with ROW_NUMBER over (order by some_col) - results automatically ordered by this ROW_NUMBER column
with ROW_NUMBER over (order by some_col desc) - results again automatically order by this ROW_NUMBER column reflecting the new direction
Why is it behaving like this? Is there an implicit order by when using ROW_NUMBER?
If this is vendor specific, I was testing on MSSQL2014
The ORDER BY Clause in the window function only controls the order of the rows considered for the window function. It does not guarantee the final result set order.
Over clause
Note: The ORDER BY clause in the OVER clause only controls the order that the rows in the partition will be utilized by the window
function. It does not control the order of the final result set.
Without an ORDER BY clause on the query itself, the order of the rows
is not guaranteed. You may notice that your query may be returning in
the order of the last specified OVER clause – this is due to the way
that this is currently implemented in SQL Server. If the SQL Server
team at Microsoft changes the way that it works, it may no longer
order your results in the manner that you are currently observing. If
you need a specific order for the result set, you must provide an
ORDER BY clause against the query itself.
I have a set of records in a table. I get records via select without any order statements just select * from table so there isn't any obvious order.
Will the order of records differs after updating some records?
There is no internal order in a Postgres database table (and this is also the case with most other RDBMS). The only order which will exist at selection time is the one you specify using an ORDER BY clause. So, the answer to your question is that you should always rely on ORDER BY if you want a consistent, reproducible order in your result set.
I have used NOT IN clause in Select Statement. When I run that query, each time it returns the same result set but the order is different.
Is this the default behavior of "NOT IN" clause?
The query which I am using is as below:
SELECT *,(ISNULL(AppFirstName,'')+' '+ISNULL(AppMiddleName,'')+' '+ISNULL(AppLastName,'')) as AppName FROM BApp AF WHERE AF.SId=11 AND AF.SCId=5 AND AF.CCId= 1 AND AF.IsActive=1 AND AF.ASId=16 AND AF.AId NOT IN (SELECT AId FROM NumberDetails where AId = AF.AId)
The order of an SQL result is not defined and left for the database to pick unless you use an ORDER clause. If you need to know more, post the query and what DB you are using.
If you don't specify an ORDER BY clause, then no query has a defined order. The database is free to return you the rows in whatever order is easiest for it.
The reason this sometimes seems consistent is that the rows will often be read out either in the order they exist on disk (probably the order they were inserted) or in the order of some index that was used to find the result.
The more complex your query, the more complex the processing the database needs to do, so the less likely the results are to come out in some obvious, repeatable, order.
Moral of the story: always use an ORDER BY clause.
SQL, by default, does not order or sort the records it returns. This behavior isn't specific to 'NOT IN', but is a general premise of the language. However, you can easily order your results by adding an 'ORDER BY table.column_name' to the end of your query.
Few days ago I came across a strange problem with the Order By , While creating a new table I used
Select - Into - From and Order By (column name)
and when I open that table see tables are not arranged accordingly.
I re-verified it multiple times to make sure I am doing the right thing.
One more thing I would like to add is till the time I don't use INTO, I can see the desired result but as soon as I create new table, I see there is no Order for tht column. Please help me !
Thanks in advance.. Before posting the question I did research for 3 days but no solution yet
SELECT
[WorkOrderID], [ProductID], [OrderQty], [StockedQty]
INTO
[AdventureWorks2012].[Production].[WorkOrder_test]
FROM
[AdventureWorks2012].[Production].[WorkOrder]
ORDER BY
[StockedQty]
SQL 101 for beginners: SELECT statements have no defined order unless you define one.
When i open that table
That likely issues a SELECT (TOP 1000 IIFC) without order.
While creating a new table i used Select - Into - From and Order By (column name)
Which sort of is totally irrelevant - you basically waste performance ordering the input data.
You want an order in a select, MAKE ONE by adding an order by clause to the select. The table's internal order is by clustered index, but an query can return results in any order it wants. Fundamental SQL issue, as I said in the first sentence. Any good book on sql covers that in one of the first chapters. SQL uses a set approach, sets have no intrinsic order.
Firstly T-SQL is a set based language and sets don't have orders. More over it also doesn't mean serial execution of commands i.e, the above query is not executed in sequence written but the processing order for a SELECT statement is as:
1.FROM
2.ON
3.JOIN
4.WHERE
5.GROUP BY
6.WITH CUBE or WITH ROLLUP
7.HAVING
8.SELECT
9.DISTINCT
10.ORDER BY
Now when you execute your query without into selected column data gets ordered based on the condition specified in 'Order By' clause but when Into is used format of new_table is determined by evaluating the expressions in the select list.(Remember order by clause has not been evaluated yet).
The columns in new_table are created in the order specified by the select list but rows cannot be ordered. It's a limitation of Into clause you can refer here:
Specifying an ORDER BY clause does not guarantee the rows are inserted
in the specified order.