I have to run a sql query that grabs the values only if two conditions are true. So for example, I need to grab all the values where asset=x and id_name=12345. There are about 10k combinations between asset and id_name that I need to be able to query for using sql. Usually I would just do the following:
select * from database where id_name IN (12345)
But how do I make this query when two conditions have to be true. id_name has to equal 12345 AND asset has to equal x.
I tried turning the list i need into tuples like this:
new_list = list(scams[['asset', 'id_name']].itertuples(index=False, name=None))
which gives me a list like this:
new_list = (12345, x), (32342, z)...etc.
Any suggestions would be great. Thanks!
Based on my understanding you need to query or fetch records based on a combination of two filters. Also you have around 10K combinations. Here is a simple SQL based solution.
Create a new column in the same table or build a temp table/view with a new column say "column_new". Populate the concatenated value of id_name and asset in the new column. You can use a concatenation function based on the database. Example in SQL server use CONCAT(column1,column2).
Now you can write your SQL as select * from database where colum_new IN ("12345x","32342z");.
Note : You can also use a "-" or "|" between column 1 and column 2 while doing a concatenation.
Related
I have two querysets -
A = Bids.objects.filter(*args,**kwargs).annotate(highest_priority=Case(*[
When(data_source=data_source, then Value(i))
for i, data_source in enumerate(data_source_order_list)
],
.order_by(
"date",
"highest_priority"
))
B= A.values("date").annotate(Min("highest_priority)).order_by("date")
First query give me all objects with selected time range with proper data sources and values. Through highest_priority i set which item should be selected. All items have additional data.
Second query gives me grouped by information about items in every date. In second query i do not have important values like price etc. So i assume i have to join these two tables and filter out where a.highest_priority = b.highest priority. Because in this case i will get queryset with objects and only one item per date.
I have tried using distinct - not working with .first()/.last(). Annotates gives me dict by grouped by, and grouping by only date cutting a lot of important data, but i have to group by only date...
Tables looks like that
A
B
How to join them? Because when i join them i could easily filter highest_prio with highest_prio and get my date with only one database shot. I want to use ORM, because i could just distinct and put it on the list and i do not want to hammer base with connecting multiple queries through date.
Look if this sugestion works :
SELECT * , (to_char(a.date, 'YYYYMMDD')::integer)*highest_priority AS prioritycalc;
FROM table A
JOIN table B ON (to_char(a.date, 'YYYYMMDD')::integer)*highest_priority = (to_char(b.date, 'YYYYMMDD')::integer)*highest_priority
ORDER BY prioritycalc DESC;
I want to get all the columns of a table with max(timestamp) and group by name.
What i have tried so far is:
normal_query ="Select max(timestamp) as time from table"
event_list = normal_query \
.distinct(Table.name)\
.filter_by(**filter_by_query) \
.filter(*queries) \
.group_by(*group_by_fields) \
.order_by('').all()
the query i get :
SELECT DISTINCT ON (schema.table.name) , max(timestamp)....
this query basically returns two columns with name and timestamp.
whereas, the query i want :
SELECT DISTINCT ON (schema.table.name) * from table order by ....
which returns all the columns in that table.Which is the expected behavior and i am able to get all the columns, how could i right it down in python to get to this statement?.Basically the asterisk is missing.
Can somebody help me?
What you seem to be after is the DISTINCT ON ... ORDER BY idiom in Postgresql for selecting greatest-n-per-group results (N = 1). So instead of grouping and aggregating just
event_list = Table.query.\
distinct(Table.name).\
filter_by(**filter_by_query).\
filter(*queries).\
order_by(Table.name, Table.timestamp.desc()).\
all()
This will end up selecting rows "grouped" by name, having the greatest timestamp value.
You do not want to use the asterisk most of the time, not in your application code anyway, unless you're doing manual ad-hoc queries. The asterisk is basically "all columns from the FROM table/relation", which might then break your assumptions later, if you add columns, reorder them, and such.
In case you'd like to order the resulting rows based on timestamp in the final result, you can use for example Query.from_self() to turn the query to a subquery, and order in the enclosing query:
event_list = Table.query.\
distinct(Table.name).\
filter_by(**filter_by_query).\
filter(*queries).\
order_by(Table.name, Table.timestamp.desc()).\
from_self().\
order_by(Table.timestamp.desc()).\
all()
I have been performing a query to count how many times in my sqlite3 database table (Users), within the column "country", the value "Australia" occurs.
australia = db.session.query(Users.country).filter_by(country="Australia").count()
I need to do this in a more dynamic way for any country value that may be within this column.
I have tried the following but unfortunately I only get a count of 0 for all values that are passed in the loop variable (each).
country = list(db.session.query(Users.country))
country_dict = list(set(country))
for each in country_dict:
print(db.session.query(Users.country).filter_by(country=(str(each))).count())
Any assistance would be greatly appreciated.
The issue is that country is a list of result tuples, not a list of strings. The end result is that the value of str(each) is something along the lines of ('Australia',), which should make it obvious why you are getting counts of 0 as results.
For when you want to extract a list of single column values, see here. When you want distinct results, use DISTINCT in SQL.
But you should not first query distinct countries and then fire a query to count the occurrence of each one. Instead use GROUP BY:
country_counts = db.session.query(Users.country, db.func.count()).\
group_by(Users.country).\
all()
for country, count in country_counts:
print(country, count)
The main thing to note is that SQLAlchemy does not hide the SQL when using the ORM, but works with it.
If you can use the sqlite3 module with direct SQL it is a simple query:
curs = con.execute("SELECT COUNT(*) FROM users WHERE country=?", ("Australia",))
nb = curs.fetchone()[0]
I am new to python and SQLALCHEMY, and I came across this doubt, whether can we filter rows of the table based on cell values of the column of same table.
example:
Sbranch=value
result=Transaction.query.filter(Transaction.branch==Sbranch)
.order_by(desc(Transaction.id)).limit(50).all()
if the value of Sbranch=0, i want to read all the rows regardless of Sbranch value, else i want to filter rows with contains Transaction.branch==Sbranch.
I know that it can be achieved by comparing the values of Sbranch(if-else conditions),but it gets complicated as the number of such columns increases.
Example:
Sbranch=value1
trans_by=value2
trans_to=value3
.
.
result=Transaction.query.filter(Transaction.branch==Sbranch,Transaction.trans_by==value2,Transaction_to==trans_to)
.order_by(desc(Transaction.id)).limit(50).all()
I want to apply similar filter with all 3 columns.
I want to know if there is any inbuilt function in SQLALCHEMY to this problem.
You can optionally add the filter based on the value of SBranch
query = Transaction.query
if SBranch != 0:
query = query.filter(Transaction.branch == SBranch)
result = query.order_by(Transaction.id.desc()).limit(50).all()
I think i found the solution, it's not the best but will reduce the work for the developers(not the processor).
Sbranch=value
branches=[]
if Sbranch==0:
# Append all the values into the array for which the rows are filtered
# for example:
branches=[1,2,4,7,3,8]
else:
branches.append(branch)
result=Transaction.query.filter(Transaction.branch.in_(branches))
.order_by(desc(Transaction.id)).limit(50).all()
I am trying to query a table in an existing sqlite database. The data must first be subsetted as such, from a user input:
query(Data.num == input)
Then I want to find the max and min of another field: date in this subset.
I have tried using func.min/max, as well as union, but received an error saying the columns do not match. One of the issues here is that func.min/max need to be used as query arguments, not filter.
ids = session.query(Data).filter(Data.num == input)
q = session.query(func.max(Data.date),
func.min(Data.date))
ids.union(q).all()
ArgumentError: All selectables passed to CompoundSelect must have identical numbers of columns; select #1 has 12 columns, select #2 has 2
Similarly, if I use func.max and min separately, the error says #2 has 1 column.
I think seeing this query in SQL might help as well.
Thanks
The following solution works. You first need to set up the query, then filter the data down afterwards.
query = session.query(Data.num, func.min(Data.date),
func.max(Data.date), Data.date)
query = query.filter(Data.num == input)
query = query.all()