I have an SQL query:
SELECT
FORMAT(datetime_scrapped, 'MMMM-yy') [date],
count(FORMAT(datetime_scrapped, 'MMMM-yy')) as quantity
FROM scrap_log
GROUP BY FORMAT(datetime_scrapped, 'MMMM-yy')
It basically summarises all the entries in the scrap_log table by month/year and counts how many entries are in each month/year. Returns two columns (date and quantity). But I need to execute this in an ASP.NET core API using Entity Framework core. I tried using .fromSqlRaw(), but this expects all columns to be returned and so doesn't work.
I can find plenty of info on EF to implement group by and count etc... But I cannot find anything for the FORMAT(datetime, "MMMM-yy") part. Please could somebody explain to me how to do this?
EDIT: Seems already I appear to be going about this the wrong way in terms of efficiency. I will look into alternative solutions based on comments already made. Thanks for the fast response.
Related
Note that PostgreSQL website mentions that it has a limit on number of columns between 250-1600 columns depending on column types.
Scenario:
Say I have data in 17 tables each table having around 100 columns. All are joinable through primary keys. Would it be okay if I select all these columns in a single select statement? The query would be pretty complex but can be programmatically generated. The reason for doing this is to get denormalised data to populate a web page. Please do not ask why though :)
Quite obviously if I do create table table1 as (<the complex select statement>), I will be hitting the limit mentioned in the website. But do simple queries also face the same restriction?
I could probably find this out by doing the exercise myself. In the next few days I probably will. However, if someone has an idea about this and the problems I might face by doing a single query, please share the knowledge.
I can't find definitive documentation to back this up, but I have
received the following error using JDBC on Postgresql 9.1 before.
org.postgresql.util.PSQLException: ERROR: target lists can have at most 1664 entries
As I say though, I can't find the documentation for that so it may
vary by release.
I've found the confirmation. The maximum is 1664.
This is one of the metrics that is available for confirmation in the INFORMATION_SCHEMA.SQL_SIZING table.
SELECT * FROM INFORMATION_SCHEMA.SQL_SIZING
WHERE SIZING_NAME = 'MAXIMUM COLUMNS IN SELECT';
2 stored procedures are developed by .net developers. which are giving same record counts when you pass the same parameter?
now due to some changes , we are getting mismatch record count i.e
if first stored procedure is giving 2 records for a paramemter , the second SP is giving only 1 record.
to find this i followed the approach like
i verified
i counted total records of a table after joining
total tables used in joining
3.distinct / group by is used in 2 tables or not?
finally i am not able to find the issue.
how do i fix it?
could any body share some ideas.
thanks in advance?
Assuming the same JOINs and filters, then the problem is NULLs.
That is, either
A WHERE clause has a direct NULL comparison which will fail
A COUNT is on a nullable column. See Count(*) vs Count(1) for more
Either way, why do you have the same very similar stored procedures written by 2 different developers, that appear to have differences?
I have been doing queries in EF and everything working great but now i have in the db 2 fields that are actually CHAR.. They hold a date but in the form of a number, in SQL Management Studio i can do date1 >= date2 for example and i can also check to see if a number i have falls in between these 2 dates.
Its nothing unusual, but basically a field that represents a date (the number grows as the date does)...
Now in EF when i try to do >= it states you can't do this on a string, ok understand its c# so i tried doing Convert.ToDecimal(date1) but it gives me an error saying that its not supported.
I have no option of changing the db fields, they are set in stone :-(
the way i got it to work was request of details and do a .ToList and then use the .ToDecimal and it works but of course this is doing it in memory! and this defeats the object of EF i.e. for example adding to the query using iqueryable.
Another way i got it to work was to pass the SQL query to SqlQuery of the dbcontext but again i lose a lot of ef functionality.
Can anyone help?
I am really stuck
As you say that you tried >= I assume that it would work for you if you could do that in plain SQL. And that is possible by doing
String.Compare(date1, date2) >= 0
EF is smart enough to translate that into a >= operator.
The advantage is that you do not need to compare converted values, so indexes can be used in execution plans.
First of all, you can at least enable deferred execution of the query by using AsEnumerable() instead of ToList(). This won't change the fact that the database would need to return all the records when you do in fact execute the query, however.
To let the database perform the filtering, you need your query to be compatible with SQL. Since you can't do ToDecimal() in SQL, you need to work with strings directly by converting your myvar to a string that is in the same format as dateStart and dateEnd, then form your query.
I'm using Zend Framework for my website and I'd like to retrieve some data from my PostgreSQL database.
I have a request like :
SELECT DISTINCT ON(e.id) e.*, f.*, g.* FROM e, f, g
WHERE e.id = f.id_e AND f.id = g.id_f
This request works well but I don't know how to convert the DISTINCT ON(e.id) with Zend.
It seems that I can get DISTINCT rows but no distinct columns.
$select->distinct()->from("e")->join("f", "e.id = f.id_e")
->join("g", "f.id = g.id_f");
Any idea on how to make a select with distinct column ?
Thanks for help
You probably can't do this with Zend Framework since distinct on is not part of the SQL standard (end of page in Postgres documentation). Although Postgres supports it, I would assume its not part of Zend Framework because you could in theory configure another database connection which does not offer support.
If you know in advance that you're developing for a specific database (Postgres in this case), you could use manually written statements instead. You'll gain more flexibility within the queries and better performance at the cost of no longer being able to switch databases.
You would then instantiate a Zend_Db_Apdapter for Postgres. There a various methods available to get results for SQL queries which are described in the frameworks documentation starting at section Reading Query Results. If you choose to go this route I'd recommend to create an own subclass of the Zend_Db_Adapter_Pgsql class. This is to be able to convert data types and throw exceptions in case of errors instead of returning ambiguous null values and hiding error causes.
I use MS SQL Server 2008 R2.
I've got the problem, please, excuse the long explanation.
We've got the SSAS cube. It is under development at this time, but it is partially working and can be accessed through excel.
There are projects: hierarchycal parent-child dimension
There are resources assigned to the project (e.g. man-hours, building materials, technic): dimension with resource types, fact M2M table ProjectId-ResourceId-UnitsCount-Cost
There are milestones for the projects: dimension with milestone types (few are defined), M2M fact table: ProjectId-MilestoneId-...milestone dates: planned/actual start/finish
This is a simplified schema.
I need to create a MS Reporting Services report with the following columns:
Project Hierarchy
several columnts with the pre-defined and "hardcoded" resource type amount. e.g the business wants to see the columnt with man-hours spent, and concrete consumption in cub-meters. Thse two clauses can be hardcoded in the query.
several columns with the pre-defined and "hardcoded" milestone type dates
this is a simplified schema too, more columns with other dimension slices are needed...
The problem is that i cannot find an elegant way to create this report.
in my current version, i have to create 2 datasets and query the resouce and milestone data in separate mdx queries.
then i need to use RS-lookup function to join the data in report outcome.
Please acvise:
is there a possibility to query this data in an single mdx query. when i try something like this:
union({{[Dim Resource].[Measure].[man-hour]} + {[Dim Resource].[Measure].[cub-meter]}},
{[Dim Milestone].[Milestone Type].[ProjectStart]}) i've got "different dimensionality" error. Any workarounds?
if i need to output a formatted value like: "X 'man-hour' / Y 'cub-meter'", i have to use lookup func to get both parts of the formula - any better way?
can i query this data any other way?
Please, indicate the direction of googling
or... should i just query the data from the source tables (this is allowed by security restrictions) with SQL
thank you in advance
Perhaps create a new 'virtual cube' to contain data from both of your existing cubes, then query that one.