I am trying to add a new property to the projection of a query using: select *, 4 Type from c, but it fails with error Syntax error, incorrect syntax near ','. Trying select c.*, 4 Type from c results in a similar error: Syntax error, incorrect syntax near '*'.
Projecting all properties manually is not really an option as not all documents contain all properties (one of the best features of DocumentDb).
How can I do so?
UPDATE
What I am trying to accomplish is something very simple in any SQL Like language. Open any relational database of your choosing and execute select *, 4 Type from [Table] and the results are very straight forward: a table with all it's columns and it's corresponding values plus an additional column named Type with all rows having the same value: 4. The difference here is that in a relational database with schema all rows in the database contain the same columns, so it is easy to enumerate the columns instead of asking for *. In a schemaless environment like documentdb you can't enumerate them because there could be unlimited combinations.
I am trying to accomplish the same thing that select c.id, 4 Type from c accomplishes, but with all properties
We solved this issue by adding a User Defined Function:
function AddType (c, v) {
c['Type'] = v;
return c;
}
and calling it SELECT value udf.AddType(c,4) FROM c.
Of course you could make this a little more generic by passing in an array instead, but hopefully the Cosmos Db team will add native support for it.
WARNING
This function adds overhead and in our internal tests it more than doubled the RUs. select * from c resulted in 90 RUs vs 220 RUs using the function above.
Related
In my android application, I use Cursor c = db.rawQuery(query, null); to query data from a local sqlite database, and one of the query string looks like the following:
SELECT t1.* FROM table t1
WHERE NOT EXISTS (
SELECT 1 FROM table t2
WHERE t2.start_time = t1.start_time AND t2.stop_time > t1.stop_time
)
however, the issue is that the query gets very slow when the database gets huge. Trying to look into introducing indexing to speed up the query, but so far, not been very successful, therefore, would be great to have some help here, as it's also hard to find examples for this for android applications.
You can create a composite index for the columns start_time and stop_time:
CREATE INDEX idx_name ON table_name(start_time, stop_time);
You can read in The SQLite Query Optimizer Overview:
The ON and USING clauses of an inner join are converted into
additional terms of the WHERE clause prior to WHERE clause analysis
...
and:
If an index is created using a statement like this:
CREATE INDEX idx_ex1 ON ex1(a,b,c,d,e,...,y,z);
Then the index might be used if the initial columns of the index
(columns a, b, and so forth) appear in WHERE clause terms. The initial
columns of the index must be used with the = or IN or IS operators.
The right-most column that is used can employ inequalities.
You may have to uninstall the app from the device so that the db is deleted and rerun to recreate it, or increase the version number of the db so that you can create the index in the onUpgrade() method.
I am trying to select data based on a status which is a string. What I want is that status 'draft' comes first, so I tried this:
SELECT *
FROM c
ORDER BY c.status = "draft" ? 0:1
I get an error:
Unsupported ORDER BY clause. ORDER BY item expression could not be mapped to a document path
I checked Microsoft site and I see this:
The ORDER BY clause requires that the indexing policy include an index for the fields being sorted. The Azure Cosmos DB query runtime supports sorting against a property name and not against computed properties.
Which I guess makes what I want to do impossible with queries... How could I achieve this? Using a stored procedure?
Edit:
About stored procedure: actually, I am just thinking about this, that would mean, I need to retrieve all data before ordering, that would be bad as I take max 100 value from my database... IS there any way I can do it so I don t have to retrieve all data first? Thanks
Thanks!
ORDER BY item expression could not be mapped to a document path.
Basically, we are told we can only sort with properties of document, not derived values. c.status = "draft" ? 0:1 is derived value.
My idea:
Two parts of query sql: The first one select c.* from c where c.status ='draft',second one select c.* from c where c.status <> 'draft' order by c.status. Finally, combine them.
Or you could try to use stored procedure you mentioned in your question to process the data from the result of select * from c order by c.status. Put draft data in front of others by if-else condition.
I have an SQLITE Database with the following tables
items(item_id,item_name,....);
tags(tag_id,tag_name);
items_tags(item_id,tag_id);
I'm using QSqlRelationalTableModel class to for the items table.
this class have this function QSqlTableModel::setFilter(const QString &filter);
The filter is a SQL WHERE clause without the keyword WHERE
for example: setFilter("item_name=arg");
what I want to do is to use the setFilter function to select only items with a specific tag/tags.
since I can only use the setFilter(QString &Filter) function which is basically a WHERE clause
I found this solution which I think is a bad one
I'll use this filter
setFilter(FilterString);
FilterString="item_id=arg1 or item_id=arg2 or item_id=argX or......"
the IDs will be obtained from this query
Query.prepare("select item_id from items_tags where tag_id=?");
the FilterString will be generated and incremented by a (do while loop) using Query.next() function that will loop over the resulted Query IDs
FilterString+="item=Query.value(item_id).toString();
and use like 2 if statements to determine when to add the or clause to the FilterString
this solution will definitely work but I think it's stupid because if there are many tagged items(say 5000) the Query string will contain 4999 or clause and another 5000 "id=x" so the Query will be more than 10000 characters long.
QString object can contain a lot more characters but is this Query will have a big impact on performance ?
what are the other alternatives, Even if it requires to switch to another DB like ORACLE or Mysql since SQLITE doesn't have many internal features
I am working on a CR where I need to create a PL/SQL package and I am bit confused about the approach.
Background : There is a View named ‘D’ which is at end of the chain of interdependent views in sequence.
We can put it as :
A – Fact table (Populated using Informatica, source MS-Dynamics)
B – View 1 based on fact table
C – View 2 based on View1
D – View 3 based on view2
Each view has multiple joins with other tables in structure along with the base view.
Requirement: Client wants to remove all these views and create a PL/SQL Package which can insert data directly from MS-Dynamics to View3 i.e., ‘D’.
Before I come up with something complex. I would like to know, is there any standard approach to address such requirements.
Any advice/suggestions are appreciated.
It should be obvious that you still need a fact table to keep some data.
You could get rid of B and C by making D more complex (the WITH clause might help to keep it overseeable).
Inserting data into D is (most likely) not possible per se, but you can create and INSTEAD OF INSERT trigger to handle that, i.e. insert into the fact table A instead.
Example for using the WITH clause:
Instead of
create view b as select * from dual;
create view c as select * from b;
create view d as select * from c;
you could write
create view d as
with b as (select * from dual),
c as (select * from b)
select * from c;
As you can see, the existing view definition goes 1:1 into the WITH clause, so it's not too difficult to create a view to combine all views.
If you are on Oracle 12c you might look at DBMS_UTILITY.EXPAND_SQL_TEXT, though you'll probably want to clean up the output a bit for readability.
A few things first
1) A view is a predefined sql query so it is not possible to insert records directly into it. Even a materialized view which is a persistant table structure only gets populated with the results of a query thus as things stand this is not possible. What is possible is to create a new table to populate the data which is currently aggregated at view D
2) It is very possible to aggregate data at muliple levels in Informatica using combination of multiple inline sorter and aggregater transformations which will generate the data at the level you're looking for.
3) Should you do it? Data warehousing best practices would say no and keep the data as granular as possible per the original table A so that it can be rolled up in many ways (refer Kimball group site and read up on star schema for such matters). Do you have much sway in the choice though?
4) The current process (while often used) is not that much better in terms of star schema
I have recently stumbled upon a problem with selecting relationship details from a 1 table and inserting into another table, i hope someone can help.
I have a table structure as follows:
ID (PK) Name ParentID<br>
1 Myname 0<br>
2 nametwo 1<br>
3 namethree 2
e.g
This is the table i need to select from and get all the relationship data. As there could be unlimited number of sub links (is there a function i can create for this to create the loop ?)
Then once i have all the data i need to insert into another table and the ID's will now have to change as the id's must go in order (e.g. i cannot have id "2" be a sub of 3 for example), i am hoping i can use the same function for selecting to do the inserting.
If you are using SQL Server 2005 or above, you may use recursive queries to get your information. Here is an example:
With tree (id, Name, ParentID, [level])
As (
Select id, Name, ParentID, 1
From [myTable]
Where ParentID = 0
Union All
Select child.id
,child.Name
,child.ParentID
,parent.[level] + 1 As [level]
From [myTable] As [child]
Inner Join [tree] As [parent]
On [child].ParentID = [parent].id)
Select * From [tree];
This query will return the row requested by the first portion (Where ParentID = 0) and all sub-rows recursively. Does this help you?
I'm not sure I understand what you want to have happen with your insert. Can you provide more information in terms of the expected result when you are done?
Good luck!
For the retrieval part, you can take a look at Common Table Expression. This feature can provide recursive operation using SQL.
For the insertion part, you can use the CTE above to regenerate the ID, and insert accordingly.
I hope this URL helps Self-Joins in SQL
This is the problem of finding the transitive closure of a graph in sql. SQL does not support this directly, which leaves you with three common strategies:
use a vendor specific SQL extension
store the Materialized Path from the root to the given node in each row
store the Nested Sets, that is the interval covered by the subtree rooted at a given node when nodes are labeled depth first
The first option is straightforward, and if you don't need database portability is probably the best. The second and third options have the advantage of being plain SQL, but require maintaining some de-normalized state. Updating a table that uses materialized paths is simple, but for fast queries your database must support indexes for prefix queries on string values. Nested sets avoid needing any string indexing features, but can require updating a lot of rows as you insert or remove nodes.
If you're fine with always using MSSQL, I'd use the vendor specific option Adrian mentioned.