In the python snowflake.connector, is it possible to see which columns have an active masking policy? the snowflake command describe table MYTABLE does show this, but in python:
running x = cur.describe('select * from MYTABLE'), the object x doesn't seem to contain information on whether a column is masked or not
try running the describe query with python.
x = cur.execute('describe table MYTABLE')
Related
I am working on Windows desktop application in Delphi using FireDAC driver and MSSQL database system. Currently, I am having a problem in understanding how multiple sessions (users) should work. Right now, I have three test users, and when I log in with any of them, every session has the same data and functionalities. I don't want that. I want that each user (each session) has different data and functionalities.
Note that this is different from distributed systems, where tasks are distributed by hosts in a network. I am not interested in distributed system. I have a desktop application.
Could someone explain how to achieve this (different users (sessions) = different data and functionalities)?
You've indicated in a comment that what you want is for a number of users o be able to see different data rows in the same table or tables
That's actually quite quite straightforward: you just need to define, for each user (or user type), the criteria which determine which data rows they are supposed to be able to see, then write a Where clause which selects only those rows. It's generally a bad idea to hard-code users's identities in a database and what data they are permitted to see and what operations they are permitted to carry out on the data.
It's hard to give a concrete example without getting into details of what you are wanting to do, but the following simple example might help.
Suppose you have a table of Customers, and one user is suposed to deal with the USA, the second user deals with France and the third with the rest of the world.
In your app, you could have an enumerated type to represent this:
type
TRegion = (rtUSA, rtFR, rtRoW); // RoW = Rest of the World
Then you could write a function to generate the Where clause of a SQL Select statement like this:
function GetRegionWhereClause(const ARegion : TRegion) : String;
begin
Result := ' Where ';
case ARegion of
rtUSA : Result := Result + ' Customer.Country = ''USA''';
rtFR : Result := Result + ' Customer.Country = ''FR''';
rtRoW : Result := Result + ' not Customer.Country in (''USA'', ''FR'')'
end; { case }
end;
You could then call GetRegionWhereClause when you generate the Sql to open the Customers table.
Similarly define for each user type what operations they are permitted to carry out on the data (Update, Insert, Delete). But implementing that would be more a question of selectively enabling and disable the gui functionality in your app to do the tasksin question.
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
I'm using the lsqlite3 lua wrapper and I'm making queries into a database. My DB has ~5million rows and the code I'm using to retrieve rows is akin to:
db = lsqlite3.open('mydb')
local temp = {}
local sql = "SELECT A,B FROM tab where FOO=BAR ORDER BY A DESC LIMIT N"
for row in db:nrows(sql) do temp[row['key']] = row['col1'] end
As you can see I'm trying to get the top N rows sorted in descending order by FOO (I want to get the top rows and then apply the LIMIT not the other way around). I indexed the column A but it doesn't seem to make much of a difference. How can I make this faster?
You need to index the column on which you filter (i.e. with the WHERE clause). THe reason is that ORDER BY comes into play after filtering, not the other way around.
So you probably should create an index on FOO.
Can you post your table schema?
UPDATE
Also you can increase the sqlite cache, e.g.:
PRAGMA cache_size=100000
You can adjust this depending on the memory available and the size of your database.
UPDATE 2
I you want to have a better understanding of how your query is handled by sqlite, you can ask it to provide you with the query plan:
http://www.sqlite.org/eqp.html
UPDATE 3
I did not understand your context properly with my initial answer. If you are to ORDER BY on some large data set, you probably want to use that index, not the previous one, so you can tell sqlite to not use the index on FOO this way:
SELECT a, b FROM foo WHERE +a > 30 ORDER BY b
Select all records, ID which is not in the list
How to make like :
query = Story.all()
query.filter('ID **NOT IN** =', [100,200,..,..])
There's no way to do this efficiently in App Engine. You should simply select everything without that filter, and filter out any matching entities in your code.
This is now supported via GQL query
The 'IN' and '!=' operators in the Python runtime are actually
implemented in the SDK and translate to multiple queries 'under the
hood'.
For example, the query "SELECT * FROM People WHERE name IN ('Bob',
'Jane')" gets translated into two queries, equivalent to running
"SELECT * FROM People WHERE name = 'Bob'" and "SELECT * FROM People
WHERE name = 'Jane'" and merging the results. Combining multiple
disjunctions multiplies the number of queries needed, so the query
"SELECT * FROM People WHERE name IN ('Bob', 'Jane') AND age != 25"
generates a total of four queries, for each of the possible conditions
(age less than or greater than 25, and name is 'Bob' or 'Jane'), then
merges them together into a single result set.
source: appengine blog
This is an old question, so I'm not sure if the ID is a non-key property. But in order to answer this:
query = Story.all()
query.filter('ID **NOT IN** =', [100,200,..,..])
...With ndb models, you can definitely query for items that are in a list. For example, see the docs here for IN and !=. Here's how to filter as the OP requested:
query = Story.filter(Story.id.IN([100,200,..,..])
We can even query for items that in a list of repeated keys:
def all(user_id):
# See if my user_id is associated with any Group.
groups_belonged_to = Group.query().filter(user_id == Group.members)
print [group.to_dict() for group in belong_to]
Some caveats:
There's docs out there that mention that in order to perform these types of queries, Datastore performs multiple queries behind the scenes, which (1) might take a while to execute, (2) take longer if you searching in repeated properties, and (3) will up your costs with more operations.
I am trying to retrieve data about groups on LDAP. As I need to paginate results, I need to run range queries. My setup uses JNDI to connect to LDAP. I am trying to run this query
(&(objectclass=group)(range=1-500))
What am I doing wrong? I know there are range based queries for LDAP,how do I modify this query for get the same?
Well paging is one thing and range is another. You page the results that you get back from the LDAP server when there are more than 1000 entries (at least that's the default in Active Directory).
MSDN has an article on how to do paged searches in .NET; hopefully you can translate that to your environment.
Range is something different. You use range when you have a multi-value-attribute (commonly the member-attribute for a group) that has a large number of values. So you can't have range in the query. You need to specify the range when you access the multi-value-attribute (then instead of just specifying member in the code accessing the property value you specify member;range=1-500 to get the first 500 values from that multivalue attribute).
Instead of Simple Paging control you may consider using Virtual List View control if your AD is version 2003 or above. Virtual List View provided advanced result sorting options and gives you more power in controlling the subset of the search result set.
This is how you need to query to get results
int start = 0;
int step = 1500;
int finish = 1499;
boolean finished = false;
String range;
String returnedAtts[] = {"member;Range=" + range};
searchCtls.setReturningAttributes(returnedAtts);
NamingEnumeration answer = readableDirContext.search(searchDN, searchFilter, searchCtls);