I have a table in db. and when i use this code
results = db().select(db.project.ALL, orderby=db.project.id, groupby=db.project.status)
I can only choose the last row in repeats. how could i choose the first one?
The select() method will return a Rows object, which is a itterable collection of Row objects. The order of which rows will apear in your results variable will vary depending on your orderby parameter passed to your select() method. If you simply want to get a single record, which is the first one out of your select(), you could change the above code to:
results = db().select(db.project.ALL, orderby=db.project.id, groupby=db.project.status).first()
But if your intent is to reverse the order of which you're getting the rows in result, add the tilde operator (~) to your orderby parameter, which will result in adding a ORDER BY ____ DESC in relational databases. Eg:
results = db().select(db.project.ALL, orderby=~db.project.id, groupby=db.project.status)
Related
Snowflake Table has 1 Variant column and loaded with 3 JSON record. The JSON records is as follows.
{"address":{"City":"Lexington","Address1":"316 Tarrar Springs Rd","Address2":null} {"address":{"City":"Hartford","Address1":"318 Springs Rd","Address2":"319 Springs Rd"} {"address":{"City":"Avon","Address1":"38 Springs Rd","Address2":[{"txtvalue":null},{"txtvalue":"Line 1"},{"Line1":"Line 1"}]}
If you look at the Address2 field in the JSON , The first one holds NULL,2nd String and 3rd one array.
When i execute the flatten query for Address 2 as one records holds array, i get only the 3rd record exploded. How to i get all 2 records with exploded value in single query.
select data:address:City::string, data:address:Address1::string, value:txtvalue::string
from add1 ,lateral flatten( input => data:address:Address2 );
When I execute the flatten query for Address 2 as one records holds array, I get only the 3rd record exploded
The default behaviour of the FLATTEN table function in Snowflake will skip any columns that do not have a structure to expand, and the OUTER argument controls this behaviour. Quoting the relevant portion from the documentation link above (emphasis mine):
OUTER => TRUE | FALSE
If FALSE, any input rows that cannot be expanded, either because they cannot be accessed in the path or because they have zero fields or entries, are completely omitted from the output.
If TRUE, exactly one row is generated for zero-row expansions (with NULL in the KEY, INDEX, and VALUE columns).
Default: FALSE
Since your VARIANT data is oddly formed, you'll need to leverage conditional expressions and data type predicates to check if the column in the expanded row is of an ARRAY type, a VARCHAR, or something else, and use the result to emit the right value.
A sample query illustrating the use of all above:
SELECT
t.v:address.City AS city
, t.v:address.Address1 AS address1
, CASE
WHEN IS_ARRAY(t.v:address.Address2) THEN f.value:txtvalue::string
ELSE t.v:address.Address2::string
END AS address2
FROM
add1 t
, LATERAL FLATTEN(INPUT => v:address.Address2, OUTER => TRUE) f;
P.s. Consider standardizing your input at ingest or source to reduce your query complexity.
Note: Your data example is inconsistent (the array of objects does not have homogenous keys), but going by your example query I've assumed that all keys of objects in the array will be named txtvalue.
Ok, I'm working on a multi-data report that merges data from many servers.
dataset1 = One of six datasets with the data I need.
ds_BusinessDays = A calendar table dataset with Specific dates and numbers that change every day/week/month.
I'm trying to use a SWITCH where MonthName(Date) from dataset1 = MonthName(Date2) from ds_BusinessDays. Then Sum the total count.
I have successfully used similar cross dataset calculations like
SUM(SWITCH when Data = "Product" then 1) / SUM(businessdaysinmonth, "ds_BusinessDays")
This was to get the Average. works like a charm.
=SUM(
SWITCH(Fields!Requested_Month.Value = MonthName(Month(First(Fields!PreviousBusinessDate.Value, "ds_BusinessDays")))
,1)
)
All Fields in ds_BusinessDays dataset are 1 entry results. Example, "PreviousBusinessDay" = "6/21/2019". So I want my code to do something like this.
When MonthName(Date) form dataset1 = MonthName(PreviousBusinessDate) from ds_BusinessDays then 1. Sum all of that up to get my a total for that month.
The problem is that FIRST and SUM are the only fields available to me when using fields from another dataset. They can't be used in an Aggregate within an Aggregate.
Is there a substitute that I can use for First in First(Fields!PreviousBusinessDate.Value, "ds_BusinessDays")?
Why are you using a SWITCH when you only have a single conditional? I think an IIF would be much easier to read. Also, if ds_BusinessDays.PreviousBusinessDate is a single entry, why do you even need FIRST? There should only be one result. If you're trying to do what I think you're trying to do, this expression should do it.
= SUM(IIF(Fields!Requested_Month.Value = MonthName(Month(Fields!PreviousBusinessDate.Value, "ds_BusinessDays")), 1, 0))
To add additional detail, a SWITCH is best used for more than 2 conditional statements. If you're only trying to compare two fields, you can just use a simple IIF. An example of when SWITCH is necessary:
=SUM(SWITCH(Fields!Date.Value = Fields!Today.Value, 1,
Fields!Date.Value = Fields!Yesterday.Value, 2,
Fields!Date.Value = Fields!Tomorrow.Value, 3,
true, 0))
This expression would check Date against three different fields and return a different count for each, ending with an always true condition that catches everything else. Your expression doesn't need a SWITCH.
This is a textual description of data for which I need to create a database design (using SQLite) for an application.
The application needs to keep a record of operations. Each operation has a Name and its list of parameters. Each parameter has its Name and a Value. However, the values of the parameters will change over the lifetime of the app (in fact the user will be able to changes them using GUI) and we want to keep a history of the values which a certain parameter has had. Furthermore, each operation can have multiple parameter sets. A parameter set is like an envelope which encompasses a set of parameter values (which all belong to the same operation) and gives this envelope a unique Number and a non-unique Description.
This is what I have so-far:
[Database model image][1]
The database model should allow me to perform these actions on the database data:
Show a list of operations - I know how to do this.
Show a list of parameters for a given operation - I know how to do this.
For a given operation, show all its parameters as columns and show the values of the parameters as rows - each row represents a different parameter value from the history of values. I'm stuck at this one.
For a given operation, show a list of all parameter sets which belong to that operation. I'm stuck at this one too.
For a given operation and for a given parameter set, get the latest values of its parameters. Stuck at this.
I'm not sure if I should re-work my database model or if I should look for proper SQL statements to accomplish the tasks above with the model that I have. Any help is greatly appreciated. Thank you.
EDIT 1
I have re-worked my database model according to a helpful advice from #Marek Herman. Thanks to that I am able to accomplish tasks 1) 2) 4).
Now I'm trying to accomplish 5) which should not be that difficult with the current database model. I have this SQL statement:
SELECT Parameter.ParameterIdentifier, ParameterValue.ParameterValue,
ParameterValueVersion.VersionNumber, ParameterValueVersion.ChangedOn
FROM ParameterValueVersion INNER JOIN
(((Operation INNER JOIN Parameter ON Operation.OperationPLC_ID = Parameter.OperationPLC_ID)
INNER JOIN ParameterSet ON Operation.OperationPLC_ID = ParameterSet.OperationPLC_ID)
INNER JOIN ParameterValue ON (ParameterSet.ID = ParameterValue.ParameterSetID) AND
(Parameter.ID = ParameterValue.ParameterID)) ON ParameterValueVersion.ID = ParameterValue.ParameterValueVersionID
WHERE (Operation.OperationPLC_ID=[opID] AND
ParameterSet.ParameterSetNumber=[parSetNum]);
where [opID] and [parSetNum] are the input parameters. This SQL statement actually only joins all these tables together on their PK->FK relationship: Operation, Parameter, ParameterSet, ParameterValue, ParameterValueVersion and filters the rows by specified OperationPLC_ID and ParameterSetNumber.
Here is an example of an output of this SQL statement. Each row shows a name of a parameter, its value, a version number of the value and date of change of that value. Some parameters only have one value (only one version -e.g., "OFFSET"). Some parameters have two values. For example "PREFILLING" has a value of "3" which was input on Oct 20, 2016 (and has a version number 1) and it also has a value of "3.5" which was input on Oct 21, 2016 and has a version number of 2. So I'd like to show only the latest versions of the values of the parameters. Any advice how to modify the SQL statement is much appreciated. Thank you.
EDIT 2
I guess I figured out how to perform 5). I had to study a bit how GROUP BY works. This did the trick:
SELECT Parameter.ParameterIdentifier, last(ParameterValue.ParameterValue) AS ParameterValue, last(ParameterValueVersion.ChangedOn) AS ChangedOn, max(ParameterValueVersion.VersionNumber) AS VersionNumber
FROM ParameterValueVersion INNER JOIN
(((Operation INNER JOIN Parameter ON Operation.OperationPLC_ID = Parameter.OperationPLC_ID)
INNER JOIN ParameterSet ON Operation.OperationPLC_ID = ParameterSet.OperationPLC_ID)
INNER JOIN ParameterValue ON (ParameterSet.ID = ParameterValue.ParameterSetID) AND
(Parameter.ID = ParameterValue.ParameterID)) ON ParameterValueVersion.ID = ParameterValue.ParameterValueVersionID
WHERE (((Operation.OperationPLC_ID)=[opID]) AND ((ParameterSet.ParameterSetNumber)=[parSetNum]))
GROUP BY Parameter.ParameterIdentifier
ORDER BY Parameter.ParameterIdentifier
Now I still need to figure out how to perform task no. 3. I'm gonna study the suggested COALESCE function. Thank you.
0) I would connect ParameterSet to Operation and Parameter and not to ParameterValue.
1) okay!
2) okay!
3) I think you can use the COALESCE() function to display the columns and then it should be possible to show all parameters with matching OperationID
4) you can do that if you do point #0
5) same as above I think
Let's say you run a SOQL aggregate query that looks like this:
select OwnerId, sum(ExpectedRevenue)val from Opportunity GROUP BY ROLLUP(OwnerId)
For whatever reason, there are no Opportunities with ExpectedRevenue fields populated.
You get a table that looks like this:
val___|OwnerId
|Id1
|Id2
|Id3
4/4 records.
(sidenote: how do you put in tabular data without it looking terrible?)
Take note that the "val" columns are all null and the last OwnerId column is also null.
There are 4 rows because SOQL returns a "total" row as well on rollups.
While looping through the AggregateResult[] that gets returned the code blows up on a line that looks like this: AggregateResult[0].get('val'); with a "System.NullPointerException: Attempt to de-reference a null object"
However, if just 1 of those users has some data, then the whole thing works. So I'm guessing that if no rows have any data in a particular column, that column does not exist at all and calls to retrieve it blow up.
So my question is how do you determine if a column exists to avoid the null reference error?
You have said that the ownerid column and the val columns are all null, therefore AggregateResult[0] is a pointer to a null object and any attempt to get a alue from that object give you the error you are having.
What I expect you want to be doing is before you run
AggregateResult[0].get('val');
you want to have an if statement say
if(AggregateResult.size() > 0)
or possibly
if(AggregateResult[0] != null)
to ensure that you are not attempting to access an empty object.
Try that and it should work. Otherwise post up a bigger code listing to look through.
Paul
If there is no data to summarize for the filters you specify in your where clause you'll get an empty list of AggregateResult back. You can test for this using list isEmpty() in Apex.
I'm writing an NHibernate criteria that selects data supporting paging. I'm using the COUNT(*) OVER() expression from SQL Server 2005(+) to get hold of the total number of available rows, as suggested by Ayende Rahien. I need that number to be able to calculate how many pages there are in total. The beauty of this solution is that I don't need to execute a second query to get hold of the row count.
However, I can't seem to manage to write a working criteria (Ayende only provides an HQL query).
Here's an SQL query that shows what I want and it works just fine. Note that I intentionally left out the actual paging logic to focus on the problem:
SELECT Items.*, COUNT(*) OVER() AS rowcount
FROM Items
Here's the HQL:
select
item, rowcount()
from
Item item
Note that the rowcount() function is registered in a custom NHibernate dialect and resolves to COUNT(*) OVER() in SQL.
A requirement is that the query is expressed using a criteria. Unfortunately, I don't know how to get it right:
var query = Session
.CreateCriteria<Item>("item")
.SetProjection(
Projections.SqlFunction("rowcount", NHibernateUtil.Int32));
Whenever I add a projection, NHibernate doesn't select item (like it would without a projection), just the rowcount() while I really need both. Also, I can't seem to project item as a whole, only it's properties and I really don't want to list all of them.
I hope someone has a solution to this. Thanks anyway.
I think it is not possible in Criteria, it has some limits.
You could get the id and load items in a subsequent query:
var query = Session
.CreateCriteria<Item>("item")
.SetProjection(Projections.ProjectionList()
.Add(Projections.SqlFunction("rowcount", NHibernateUtil.Int32))
.Add(Projections.Id()));
If you don't like it, use HQL, you can set the maximal number of results there too:
IList<Item> result = Session
.CreateQuery("select item, rowcount() from item where ..." )
.SetMaxResult(100)
.List<Item>();
Use CreateMultiCriteria.
You can execute 2 simple statements with only one hit to the DB that way.
I am wondering why using Criteria is a requirement. Can't you use session.CreateSQLQuery? If you really must do it in one query, I would have suggested pulling back the Item objects and the count, like:
select {item.*}, count(*) over()
from Item {item}
...this way you can get back Item objects from your query, along with the count. If you experience a problem with Hibernate's caching, you can also configure the query spaces (entity/table caches) associated with a native query so that stale query cache entries will be cleared automatically.
If I understand your question properly, I have a solution. I struggled quite a bit with this same problem.
Let me quickly describe the problem I had, to make sure we're on the same page. My problem came down to paging. I want to display 10 records in the UI, but I also want to know the total number of records that matched the filter criteria. I wanted to accomplish this using the NH criteria API, but when adding a projection for row count, my query no longer worked, and I wouldn't get any results (I don't remember the specific error, but it sounds like what you're getting).
Here's my solution (copy & paste from my current production code). Note that "SessionError" is the name of the business entity I'm retrieving paged data for, according to 3 filter criterion: IsDev, IsRead, and IsResolved.
ICriteria crit = CurrentSession.CreateCriteria(typeof (SessionError))
.Add(Restrictions.Eq("WebApp", this));
if (isDev.HasValue)
crit.Add(Restrictions.Eq("IsDev", isDev.Value));
if (isRead.HasValue)
crit.Add(Restrictions.Eq("IsRead", isRead.Value));
if (isResolved.HasValue)
crit.Add(Restrictions.Eq("IsResolved", isResolved.Value));
// Order by most recent
crit.AddOrder(Order.Desc("DateCreated"));
// Copy the ICriteria query to get a row count as well
ICriteria critCount = CriteriaTransformer.Clone(crit)
.SetProjection(Projections.RowCountInt64());
critCount.Orders.Clear();
// NOW add the paging vars to the original query
crit = crit
.SetMaxResults(pageSize)
.SetFirstResult(pageNum_oneBased * pageSize);
// Set up a multi criteria to get your data in a single trip to the database
IMultiCriteria multCrit = CurrentSession.CreateMultiCriteria()
.Add(crit)
.Add(critCount);
// Get the results
IList results = multCrit.List();
List<SessionError> sessionErrors = new List<SessionError>();
foreach (SessionError sessErr in ((IList)results[0]))
sessionErrors.Add(sessErr);
numResults = (long)((IList)results[1])[0];
So I create my base criteria, with optional restrictions. Then I CLONE it, and add a row count projection to the CLONED criteria. Note that I clone it before I add the paging restrictions. Then I set up an IMultiCriteria to contain the original and cloned ICriteria objects, and use the IMultiCriteria to execute both of them. Now I have my paged data from the original ICriteria (and I only dragged the data I need across the wire), and also a raw count of how many actual records matched my criteria (useful for display or creating paging links, or whatever). This strategy has worked well for me. I hope this is helpful.
I would suggest investigating custom result transformer by calling SetResultTransformer() on your session.
Create a formula property in the class mapping:
<property name="TotalRecords" formula="count(*) over()" type="Int32" not-null="true"/>;
IList<...> result = criteria.SetFirstResult(skip).SetMaxResults(take).List<...>();
totalRecords = (result != null && result.Count > 0) ? result[0].TotalRecords : 0;
return result;