MyModel.objects.filter(name="my name", date__lte=datetime.now()).query
Outputs:
SELECT "mymodel"."id", "mymodel"."name", "mymodel"."date"
FROM "mymodel"
WHERE ("mymodel"."name" = my name AND "mymodel"."date" <= 2016-02-24 20:24:00.456974+00:00)
Which is not a valid SQL (filter parameters are unquoted).
How can I get the exact SQL that will be executed, which is:
SELECT "mymodel"."id", "mymodel"."name", "mymodel"."date"
FROM "mymodel"
WHERE ("mymodel"."name" = 'my name' AND "mymodel"."date" <= '2016-02-24 20:24:00.456974+00:00'::timestamptz)
This isn't fully answering it, but for my purposes I wanted to be able to rerun the query as raw sql. I was able to get sql and params using:
queryset = MyModel.objects.filter(name="my name", date__lte=datetime.now())
sql, sql_params = queryset.query.get_compiler(using=queryset.db).as_sql()
Then I could use these values to rerun the query as raw:
MyModel.objects.raw(sql, sql_params)
Related
I am very new to sql and intermediate at python. Using sqlite3, how can I get a print() list of of primary and foreign keys (per table) in my database?
Using Python2.7, SQLite3, PyCharm.
sqlite3.version = 2.6.0
sqlite3.sqlite_version = 3.8.11
Also note: when I set up the database, I enabled FKs as such:
conn = sqlite3.connect(db_file)
conn.execute('pragma foreign_keys=ON')
I tried the following:
conn=sqlite3.connect(db_path)
print(conn.execute("PRAGMA table_info"))
print(conn.execute("PRAGMA foreign_key_list"))
Which returned:
<sqlite3.Cursor object at 0x0000000002FCBDC0>
<sqlite3.Cursor object at 0x0000000002FCBDC0>
I also tried the following, which prints nothing (but I think this may be because it's a dummy database with tables and fields but no records):
conn=sqlite3.connect(db_path)
rows = conn.execute('PRAGMA table_info')
for r in rows:
print r
rows2 = conn.execute('PRAGMA foreign_key_list')
for r2 in rows2:
print r2
Unknown or malformed PRAGMA statements are ignored.
The problem with your PRAGMAs is that the table name is missing. You have to get a list of all tables, and then execute those PRAGMAs for each one:
rows = db.execute("SELECT name FROM sqlite_master WHERE type = 'table'")
tables = [row[0] for row in rows]
def sql_identifier(s):
return '"' + s.replace('"', '""') + '"'
for table in tables:
print("table: " + table)
rows = db.execute("PRAGMA table_info({})".format(sql_identifier(table)))
print(rows.fetchall())
rows = db.execute("PRAGMA foreign_key_list({})".format(sql_identifier(table)))
print(rows.fetchall())
SELECT
name
FROM
sqlite_master
WHERE
type ='table' AND
name NOT LIKE 'sqlite_%';
this sql will show all table in database, for eache table run sql PRAGMA table_info(your_table_name);, you can get the primary key of the table.
Those pictures show what sql result like in my database:
first sql result
second sql result
I want to get a list of the latest purchase of each customer, sorted by the date.
The following query does what I want except for the date:
(Purchase.objects
.all()
.distinct('customer')
.order_by('customer', '-date'))
It produces a query like:
SELECT DISTINCT ON
"shop_purchase.customer_id"
"shop_purchase.id"
"shop_purchase.date"
FROM "shop_purchase"
ORDER BY "shop_purchase.customer_id" ASC,
"shop_purchase.date" DESC;
I am forced to use customer_id as the first ORDER BY expression because of DISTINCT ON.
I want to sort by the date, so what the query I really need should look like this:
SELECT * FROM (
SELECT DISTINCT ON
"shop_purchase.customer_id"
"shop_purchase.id"
"shop_purchase.date"
FROM "shop_purchase"
ORDER BY "shop_purchase.customer_id" ASC,
"shop_purchase.date" DESC;
)
AS result
ORDER BY date DESC;
I don't want to sort using python because I still got to page limit the query. There can be tens of thousands of rows in the database.
In fact it is currently sorted by in python now and is causing very long page load times, so that's why I'm trying to fix this.
Basically I want something like this https://stackoverflow.com/a/9796104/242969. Is it possible to express it with django querysets instead of writing raw SQL?
The actual models and methods are several pages long, but here is the set of models required for the queryset above.
class Customer(models.Model):
user = models.OneToOneField(User)
class Purchase(models.Model):
customer = models.ForeignKey(Customer)
date = models.DateField(auto_now_add=True)
item = models.CharField(max_length=255)
If I have data like:
Customer A -
Purchase(item=Chair, date=January),
Purchase(item=Table, date=February)
Customer B -
Purchase(item=Speakers, date=January),
Purchase(item=Monitor, date=May)
Customer C -
Purchase(item=Laptop, date=March),
Purchase(item=Printer, date=April)
I want to be able to extract the following:
Purchase(item=Monitor, date=May)
Purchase(item=Printer, date=April)
Purchase(item=Table, date=February)
There is at most one purchase in the list per customer. The purchase is each customer's latest. It is sorted by latest date.
This query will be able to extract that:
SELECT * FROM (
SELECT DISTINCT ON
"shop_purchase.customer_id"
"shop_purchase.id"
"shop_purchase.date"
FROM "shop_purchase"
ORDER BY "shop_purchase.customer_id" ASC,
"shop_purchase.date" DESC;
)
AS result
ORDER BY date DESC;
I'm trying to find a way not to have to use raw SQL to achieve this result.
This may not be exactly what you're looking for, but it might get you closer. Take a look at Django's annotate.
Here is an example of something that may help:
from django.db.models import Max
Customer.objects.all().annotate(most_recent_purchase=Max('purchase__date'))
This will give you a list of your customer models each one of which will have a new attribute called "most_recent_purchase" and will contain the date on which they made their last purchase. The sql produced looks like this:
SELECT "demo_customer"."id",
"demo_customer"."user_id",
MAX("demo_purchase"."date") AS "most_recent_purchase"
FROM "demo_customer"
LEFT OUTER JOIN "demo_purchase" ON ("demo_customer"."id" = "demo_purchase"."customer_id")
GROUP BY "demo_customer"."id",
"demo_customer"."user_id"
Another option, would be adding a property to your customer model that would look something like this:
#property
def latest_purchase(self):
return self.purchase_set.order_by('-date')[0]
You would obviously need to handle the case where there aren't any purchases in this property, and this would potentially not perform very well (since you would be running one query for each customer to get their latest purchase).
I've used both of these techniques in the past and they've both worked fine in different situations. I hope this helps. Best of luck!
Whenever there is a difficult query to write using Django ORM, I first try the query in psql(or whatever client you use). The SQL that you want is not this:
SELECT * FROM (
SELECT DISTINCT ON
"shop_purchase.customer_id" "shop_purchase.id" "shop_purchase.date"
FROM "shop_purchase"
ORDER BY "shop_purchase.customer_id" ASC, "shop_purchase.date" DESC;
) AS result
ORDER BY date DESC;
In the above SQL, the inner SQL is looking for distinct on a combination of (customer_id, id, and date) and since id will be unique for all, you will get all records from the table. I am assuming id is the primary key as per convention.
If you need to find the last purchase of every customer, you need to do something like:
SELECT "shop_purchase.customer_id", max("shop_purchase.date")
FROM shop_purchase
GROUP BY 1
But the problem with the above query is that it will give you only the customer name and date. Using that will not help you in finding the records when you use these results in a subquery.
To use IN you need a list of unique parameters to identify a record, e.g., id
If in your records id is a serial key, then you can leverage the fact that the latest date will be the maximum id as well. So your SQL becomes:
SELECT max("shop_purchase.id")
FROM shop_purchase
GROUP BY "shop_purchase.customer_id";
Note that I kept only one field (id) in the selected clause to use it in a subquery using IN.
The complete SQL will now be:
SELECT *
FROM shop_customer
WHERE "shop_customer.id" IN
(SELECT max("shop_purchase.id")
FROM shop_purchase
GROUP BY "shop_purchase.customer_id");
and using the Django ORM it looks like:
(Purchase.objects.filter(
id__in=Purchase.objects
.values('customer_id')
.annotate(latest=Max('id'))
.values_list('latest', flat=True)))
Hope it helps!
I have a similar situation and this is how I'm planning to go about it:
query = Purchase.objects.distinct('customer').order_by('customer').query
query = 'SELECT * FROM ({}) AS result ORDER BY sent DESC'.format(query)
return Purchase.objects.raw(query)
Upside it gives me the query I want. Downside is that it is raw query and I can't append any other queryset filters.
This is my approach if I need some subset of data (N items) along with the Django query. This is example using PostgreSQL and handy json_build_object() function (Postgres 9.4+), but same way you can use other aggregate function in other database system. For older PostgreSQL versions you can use combination of array_agg() and array_to_string() functions.
Imagine you have Article and Comment models and along with every article in the list you want to select 3 recent comments (change LIMIT 3 to adjust size of subset or ORDER BY c.id DESC to change sorting of subset).
qs = Article.objects.all()
qs = qs.extra(select = {
'recent_comments': """
SELECT
json_build_object('comments',
array_agg(
json_build_object('id', id, 'user_id', user_id, 'body', body)
)
)
FROM (
SELECT
c.id,
c.user_id,
c.body
FROM app_comment c
WHERE c.article_id = app_article.id
ORDER BY c.id DESC
LIMIT 3
) sub
"""
})
for article in qs:
print(article.recent_comments)
# Output:
# {u'comments': [{u'user_id': 1, u'id': 3, u'body': u'foo'}, {u'user_id': 1, u'id': 2, u'body': u'bar'}, {u'user_id': 1, u'id': 1, u'body': u'joe'}]}
# ....
I have the following method:
def select_query(self):
sql = "SELECT * FROM {t} WHERE 1".format(t=self._meta.db_table)
for column_name in self.distinguishing_column_names():
sql = sql + " AND {c} = {v}".format(c=column_name, v=getattr(self, column_name))
return sql
This will give me a query like this:
SELECT * FROM customer WHERE 1 AND name = JOHN SMITH AND customer_number = 11423 AND social_security_number = 1234567890 AND phone = 2323523353
Obviously, that's not going to work. Is there a way to get Django to quote this for me?
Note: I'm not asking for a prepared statement. That's something different.
Do you need to return a query this way? The proper way would be to call cursor with the query and the params as argument:
Does Python support MySQL prepared statements?
The correct way to format a query seems to be:
query = query % db.literal(args)
Where db is a mysql.Connection (or presumably any connection)
Apparently the answer is "no."
I was following the documentation on FullTextSearch in postgresql. I've created a tsvector column and added the information i needed, and finally i've created an index.
Now, to do the search i have to execute a query like this
SELECT *, ts_rank_cd(textsearchable_index_col, query) AS rank
FROM client, plainto_tsquery('famille age') query
WHERE textsearchable_index_col ## query
ORDER BY rank DESC LIMIT 10;
I want to be able to execute this with Django's ORM so i could get the objects. (A little question here: do i need to add the tsvector column to my model?)
My guess is that i should use extra() to change the "where" and "tables" in the queryset
Maybe if i change the query to this, it would be easier:
SELECT * FROM client
WHERE plainto_tsquery('famille age') ## textsearchable_index_col
ORDER BY ts_rank_cd(textsearchable_index_col, plainto_tsquery(text_search)) DESC LIMIT 10
so id' have to do something like:
Client.objects.???.extra(where=[???])
Thxs for your help :)
Another thing, i'm using Django 1.1
Caveat: I'm writing this on a wobbly train, with a headcold, but this should do the trick:
where_statement = """plainto_tsquery('%s') ## textsearchable_index_col
ORDER BY ts_rank_cd(textsearchable_index_col,
plainto_tsquery(%s))
DESC LIMIT 10"""
qs = Client.objects.extra(where=[where_statement],
params=['famille age', 'famille age'])
If you were on Django 1.2 you could just call:
Client.objects.raw("""
SELECT *, ts_rank_cd(textsearchable_index_col, query) AS rank
FROM client, plainto_tsquery('famille age') query
WHERE textsearchable_index_col ## query
ORDER BY rank DESC LIMIT 10;""")
I'm using the sqlite3 library in c++ to query the database from *.sqlite file. can you write a query statement in sqlite3 like:
char* sql = "select name from table id = (select full_name from second_table where column = 4);"
The second statement should return an id to complete the query statement with first statement.
Yes you can, just make sure that the nested query doesn't return more than one row. Add a LIMIT 1 to the end of the nested query to fix this. Also make sure that it always returns a row, or else the main query will not work.
If you want to match several rows in the nested query, then you can use either IN, like so:
char* sql = "select name from table WHERE id IN (select full_name from second_table where column = 4);"
or you can use JOIN:
char* sql = "select name from table JOIN second_table ON table.id = second_table.full_name WHERE second_table.column = 4"
Note that the IN method can be very slow, and that JOIN can be very fast, if you index on the right columns
On a sidenote, you can use SQLiteadmin (http://sqliteadmin.orbmu2k.de/) to view the database and make queries directly in it (useful for testing etc).