In my DB, I've basically 3 tables:
usergroup(id, name, deleted)
usergroup_presentation(id, groupid, presentationid)
presentation(id, name)
I'm trying to run this DAL query:
left_join = db.usergroup_presentation.on((db.usergroup_presentation.group_id==db.usergroup.id)
&(db.usergroup_presentation.presentation_id==db.presentation.id))
result = db(db.usergroup.deleted==False).select(
db.usergroup.id,
db.usergroup.name,
db.usergroup_presentation.id,
left=left_join,
orderby=db.usergroup.name)
And SQL returns this errors: Unknown column 'presentation.id' in 'on clause'
The generated SQL looks something like that:
SELECT usergroup.id, usergroup.name, usergroup_presentation.id
FROM presentation, usergroup
LEFT JOIN usergroup_presentation ON ((usergroup_presentation.group_id = usergroup.id) AND (usergroup_presentation.presentation_id = presentation.id))
WHERE (usergroup.deleted = 'F')
ORDER BY usergroup.name;
I did some researches on Google and I got this:
http://mysqljoin.com/joins/joins-in-mysql-5-1054-unknown-column-in-on-clause/
Then I tried to run this query directly in my DB:
SELECT usergroup.id, usergroup.name, usergroup_presentation.id
FROM (presentation, usergroup)
LEFT JOIN usergroup_presentation ON ((usergroup_presentation.group_id = usergroup.id) AND (usergroup_presentation.presentation_id = presentation.id))
WHERE (usergroup.deleted = 'F')
ORDER BY usergroup.name;
And indeed it works when adding the brackets around the FROM tables.
My question is how can I generate a SQL query like this (with brackets) with DAL without executing a basic executesql ?
Even better, I would like to get a cleaner SQL query using INNER JOIN and LEFT JOIN. I don't know if it's possible with my query though.
I believe this has now been fixed in trunk. Please help us check it. P.S. next time open a ticket (https://code.google.com/p/web2py/issues/list) and it will be fixed sooner.
Related
I try to join a second table (PageLikes) on a first Table (PageVisits) after selecting only distinct values on one column of the first table with the python ORM peewee.
In pure SQL I can do this:
SELECT DISTINCT(pagevisits.visitor_id), pagelikes.liked_item FROM pagevisits
INNER JOIN pagelikes on pagevisits.visitor_id = pagelikes.user_id
In peewee with python I have tried:
query = (Page.select(
fn.Distinct(Pagevisits.visitor_id),
PageLikes.liked_item)
.join(PageLIkes)
This gives me an error:
distinct() takes 1 positional argument but 2 were given
The only way I can and have used distinct with peewee is like this:
query = (Page.select(
Pagevisits.visitor_id,
PageLikes.liked_item)
.distinct()
which does not seem to work for my scenario.
So how can I select only distinct values in one table based on one column before I join another table with peewee?
I don't believe you should be encountering an error using fn.DISTINCT() in that way. I'm curious to see the full traceback. In my testing locally, I have no problems running something like:
query = (PageVisits
.select(fn.DISTINCT(PageVisits.visitor_id), PageLikes.liked_item)
.join(PageLikes))
Which produces SQL equivalent to what you're after. I'm using the latest peewee code btw.
As Papooch suggested, calling distinct on the Model seems to work:
distinct_visitors = (Pagevisits
.select(
Pagevisits.visitor_id.distinct().alias("visitor")
)
.where(Pagevisits.page_id == "Some specifc page")
.alias('distinct_visitors')
)
query = (Pagelikes
.select(fn.Count(Pagelikes.liked_item),
)
.join(distinct_visitors, on=(distinct_visitors.c.visitor = Pagelikes.user_id))
.group_by(Pagelikes.liked_item)
)
Confused working with query object results. I am not using foreign keys in this example.
lookuplocation = aliased(ValuePair)
lookupoccupation = aliased(ValuePair)
persons = db.session.query(Person.lastname, lookuplocation.displaytext, lookupoccupation.displaytext).\
outerjoin(lookuplocation, Person.location == lookuplocation.valuepairid).\
outerjoin(lookupoccupation, Person.occupation1 == lookupoccupation.valuepairid).all()
Results are correct as far as data is concerned. However, when I try to access an individual row of data I have an issue:
persons[0].lastname works as I expected and returns data.
However, there is a person.displaytext in the result but since I aliased the displaytext entity, I get just one result. I understand why I get the result but I need to know what aliased field names I would use to get the two displaytext columns.
The actual SQL statement generated by the above join is as follows:
SELECT person.lastname AS person_lastname, valuepair_1.displaytext AS valuepair_1_displaytext, valuepair_2.displaytext AS valuepair_2_displaytext
FROM person LEFT OUTER JOIN valuepair AS valuepair_1 ON person.location = valuepair_1.valuepairid LEFT OUTER JOIN valuepair AS valuepair_2 ON person.occupation1 = valuepair_2.valuepairid
But none of these "as" field names are available to me in the results.
I'm new to SqlAlchemy so most likely this is a "newbie" issue.
Thanks.
Sorry - RTFM issue - should have been:
lookuplocation.displaytext.label("myfield1"),
lookupoccupation.displaytext.label("myfield2")
After results are returned reference field with person.myfield
Simple.
In this example, I am using the sample MySQL classicmodels database.
So I have two queries:
products = session.query(Products)
orderdetails = session.query(OrderDetails)
Let's assume I cannot make any more queries to the database after this and I can only join these two queries from this point on.
I want to do an outer join on them to be able to do something like this:
for orderdetail, product in query:
print product.productName, product.productCode, orderdetails.quantityOrdered
However, whenever I do an outerjoin on this, I can only seem to get a left join.
query = orderdetails.outerjoin(Products)
Code like this yields only orderdetails columns:
for q in query:
# Only gives orderdetails columns
print q
And doing something like this:
for orderdetails, product in query:
print orderdetails, product
Gives me an error: TypeError: 'OrderDetails' object is not iterable.
What am I doing wrong? I just want columns from the Products table as well.
EDIT:
I have found my solution thanks to #univerio's answer. My real goal was to do a join on two existing queries and then do a SUM and COUNT operation on them.
SQLAlchemy basically just transforms a query object to a SQL statement. The with_entities function just changes the SELECT expression to whatever you pass to it. This is my updated solution, which includes unpacking and reading the join:
for productCode, numOrders, quantityOrdered in orderdetails.with_entities(
OrderDetails.productCode,
func.count(OrderDetails.productCode),
func.sum(OrderDetails.quantityOrdered)).group_by(OrderDetails.productCode):
print productCode, numOrders, quantityOrdered
You can overwrite the entity list with with_entities():
orderdetails.outerjoin(Products).with_entities(OrderDetails, Products)
I am using PeeWee with MySQL. I have two tables that need a full join to keep records from both left and right sides. MySQL doesn't support this directly, but I have used "Method 2" in this helpful artice - http://www.xaprb.com/blog/2006/05/26/how-to-write-full-outer-join-in-mysql/ to create a Full Join SQL statement that seems to work for my data.
It requires a "UNION ALL" of "LEFT OUTER JOIN" and "RIGHT OUTER JOIN", using an excusion of duplicate data in the 2nd result set.
I'm matching up backup-tape barcodes in the two tables.
SQL
SELECT * FROM mediarecall AS mr
LEFT OUTER JOIN media AS m ON mr.alternateCode = m.tapeLabel
UNION ALL
SELECT * FROM mediarecall AS mr
RIGHT OUTER JOIN media AS m ON mr.alternateCode = m.tapeLabel
WHERE mr.alternateCode IS NULL
However, when I come to bring this into my python script using PeeWee, I discovered that there doesn't seem to be a JOIN.RIGHT_OUTER to allow me to re-create this SQL. I have used plently of JOIN.LEFT_OUTER in the past, but this is the first time I have needed a Full Join.
I can make PeeWee work with a RawQuery(), of course, but I'd love to keep my code looking more elegant if I can.
Has anyone managed to re-create a Full Join with MySQL and PeeWee without resorting to RawQuery?
I had envisaged something like the following (which I know is invalid):-
left_media = (MediaRecall
.select()
.join(Media,JOIN.LEFT_OUTER,
on=(MediaRecall.alternateCode == Media.tapeLabel)
)
)
right_media = (MediaRecall
.select()
.join(Media,JOIN.RIGHT_OUTER,
on=(MediaRecall.alternateCode == Media.tapeLabel)
)
)
.where(MediaRecall.alternateCode >> None) # Exclude duplicates
all_media = ( left_media | right_media) # UNION of the 2 results, which I
# can then use .where(), etc on
You can add support for right outer:
from peewee import JOIN
JOIN['RIGHT_OUTER'] = 'RIGHT OUTER'
Then you can use JOIN.RIGHT_OUTER.
I am using Python with SQLite 3. I have user entered SQL queries and need to format the results of those for a template language.
So, basically, I need to use .description of the DB API cursor (PEP 249), but I need to get both the column names and the table names, since the users often do joins.
The obvious answer, i.e. to read the table definitions, is not possible -- many of the tables have the same column names.
I also need some intelligent behaviour on the column/table names for aggregate functions like avg(field)...
The only solution I can come up with is to use an SQL parser and analyse the SELECT statement (sigh), but I haven't found any SQL parser for Python that seems really good?
I haven't found anything in the documentation or anyone else with the same problem, so I might have missed something obvious?
Edit: To be clear -- the problem is to find the result of an SQL select, where the select statement is supplied by a user in a user interface. I have no control of it. As I noted above, it doesn't help to read the table definitions.
Python's DB API only specifies column names for the cursor.description (and none of the RDBMS implementations of this API will return table names for queries...I'll show you why).
What you're asking for is very hard, and only even approachable with an SQL parser...and even then there are many situations where even the concept of which "Table" a column is from may not make much sense.
Consider these SQL statements:
Which table is today from?
SELECT DATE('now') AS today FROM TableA FULL JOIN TableB
ON TableA.col1 = TableB.col1;
Which table is myConst from?
SELECT 1 AS myConst;
Which table is myCalc from?
SELECT a+b AS myCalc FROM (select t1.col1 AS a, t2.col2 AS b
FROM table1 AS t1
LEFT OUTER JOIN table2 AS t2 on t1.col2 = t2.col2);
Which table is myCol from?
SELECT SUM(a) as myCol FROM (SELECT a FROM table1 UNION SELECT b FROM table2);
The above were very simple SQL statements for which you either have to make up a "table", or arbitrarily pick one...even if you had an SQL parser!
What SQL gives you is a set of data back as results. The elements in this set can not necessarily be attributed to specific database tables. You probably need to rethink your approach to this problem.