We Keep Coding

loop over all tables in mysql databases

I am new with MySQL and I need some help please. I am using MySQL connector to write scripts.
I have database contain 7K tables and I am trying to select some values from some of these tables
cursor.execute( "SELECT SUM(VOLUME) FROM stat_20030103 WHERE company ='Apple'")
for (Volume,) in cursor:
print(Volume)
This works for one table e.g (stats_20030103). However I want to sum all volume of all tables .startwith (stats_2016) where the company name is Apple. How I can loop over my tables?

I'm not an expert in MySQL, but here is something quick and simple in python:
# Get all the tables starting with "stats_2016" and store them
cursor.execute("SHOW TABLES LIKE 'stats_2016%'")
tables = [v for (v, ) in cursor]
# Iterate over all tables, store the volumes sum
all_volumes = list()
for t in tables:
cursor.execute("SELECT SUM(VOLUME) FROM %s WHERE company = 'Apple'" % t)
# Get the first row as is the sum, or 0 if None rows found
all_volumes.append(cursor.fetchone()[0] or 0)
# Return the sum of all volumes
print(sum(all_volumes))

You can probably use select * from information_schema.tables to get all tables name into your query.

I'd try to left-join.
SELECT tables.*, stat.company, SUM(stat.volume) AS volume
FROM information_schema.tables AS tables LEFT JOIN mydb.stat_20030103 AS stat
WHERE tables.schema = "mydb" GROUP BY stat.company;
This will give you all results at once. Maybe MySQL doesn't support joining from metatables, in which case you might select it into a temporary table.
CREATE TEMPORARY TABLE mydb.tables SELECT name FROM information_schema.tables WHERE schema = "mydb"
See MySQL doc on information_schema.table.

Can we make correlated queries with SQLAlchemy

I'm trying to translate this SQL query into a Flask-SQLAlchemy call:
SELECT *
FROM "ENVOI"
WHERE "ID_ENVOI" IN (SELECT d."ID_ENVOI"
FROM "DECLANCHEMENT" d
WHERE d."STATUS" = 0
AND d."DATE" = (SELECT max("DECLANCHEMENT"."DATE")
FROM "DECLANCHEMENT"
WHERE "DECLANCHEMENT"."ID_ENVOI" = d."ID_ENVOI"))
As you can see, it uses subqueries and, most important part, one of the subqueries is a correlated query (it use d table defined in an outer query).
I know how to use subqueries with subquery() function, but I can't find documentation about correlated queries with SQLAlchemy. Do you know a way to do it ?

Yes, we can.
Have a look at the following example (especially the correlate method call):
from sqlalchemy import select, func, table, Column, Integer
table1 = table('table1', Column('col', Integer))
table2 = table('table2', Column('col', Integer))
subquery = select(
[func.if_(table1.c.col == 1, table2.c.col, None)]
).correlate(table1)
query = (
select([table1.c.col,
subquery.label('subquery')])
.select_from(table1)
)
if __name__ == '__main__':
print(query)
will result in the following query
SELECT table1.col, (SELECT if(table1.col = :col_1, table2.col, NULL) AS if_1
FROM table2) AS subquery
FROM table1
As you can see, if you call correlate on a select, the given Table will not be added to it's FROM-clause.
You have to do this even when you specify select_from directly, as SQLAlchemy will happily add any table it finds in the columns.

Based on the link from univerio's comment, I've done this code for my request:
Declch = db.aliased(Declanchement)
maxdate_sub = db.select([db.func.max(Declanchement.date)])\
.where(Declanchement.id_envoi == Declch.id_envoi)
decs_sub = db.session.query(Declch.id_envoi)\
.filter(Declch.status == SMS_EN_ATTENTE)\
.filter(Declch.date < since)\
.filter(Declch.date == maxdate_sub).subquery()
envs = Envoi.query.filter(Envoi.id_envoi.in_(decs_sub)).all()

How to use NOT IN clause in sqlalchemy ORM query

how do i convert the following mysql query to sqlalchemy?
SELECT * FROM `table_a` ta, `table_b` tb where 1
AND ta.id = tb.id
AND ta.id not in (select id from `table_c`)
so far i have this for sqlalchemy:
query = session.query(table_a, table_b)
query = query.filter(table_a.id == table_b.id)

The ORM internals describe the not_in() operator (previously notin_()), so you can say:
query = query.filter(table_a.id.not_in(subquery))
# ^^^^^^
From the docs:
inherited from the ColumnOperators.not_in() method of ColumnOperators
implement the NOT IN operator.
This is equivalent to using negation with ColumnOperators.in_(), i.e. ~x.in_(y).
Note that version 1.4 states:
The not_in() operator is renamed from notin_() in previous releases. The previous name remains available for backwards compatibility.
So you may find notin_() in some cases.

Try this:
subquery = session.query(table_c.id)
query = query.filter(~table_a.id.in_(subquery))
Note: table_a, table_b and table_c should be mapped classes, not Table instances.

here is the full code:
#join table_a and table_b
query = session.query(table_a, table_b)
query = query.filter(table_a.id == table_b.id)
# create subquery
subquery = session.query(table_c.id)
# select all from table_a not in subquery
query = query.filter(~table_a.id.in_(subquery))

MySQL - Match two tables contains HUGE DATA and find the similar data

I have two tables in my SQL.
Table 1 contains many data, but Table 2 contains huge data.
Here's the code I implement using Python
import MySQLdb
db = MySQLdb.connect(host = "localhost", user = "root", passwd="", db="fak")
cursor = db.cursor()
#Execute SQL Statement:
cursor.execute("SELECT invention_title FROM auip_wipo_sample WHERE invention_title IN (SELECT invention_title FROM us_pat_2005_to_2012)")
#Get the result set as a tuple:
result = cursor.fetchall()
#Iterate through results and print:
for record in result:
print record
print "Finish."
#Finish dealing with the database and close it
db.commit()
db.close()
However, it takes so long. I have run the Python script for 1 hour, and it still doesn't give me any results yet.
Please help me.

Do you have index on invention_title in both tables? If not, then create it:
ALTER TABLE auip_wipo_sample ADD KEY (`invention_title`);
ALTER TABLE us_pat_2005_to_2012 ADD KEY (`invention_title`);
Then combine your query into one which don't use subqueries:
SELECT invention_title FROM auip_wipo_sample
INNER JOIN us_pat_2005_to_2012 ON auip_wipo_sample.invention_title = us_pat_2005_to_2012.invention_title
And let me know about your results.

How to count rows with SELECT COUNT(*) with SQLAlchemy?

I'd like to know if it's possible to generate a SELECT COUNT(*) FROM TABLE statement in SQLAlchemy without explicitly asking for it with execute().
If I use:
session.query(table).count()
then it generates something like:
SELECT count(*) AS count_1 FROM
(SELECT table.col1 as col1, table.col2 as col2, ... from table)
which is significantly slower in MySQL with InnoDB. I am looking for a solution that doesn't require the table to have a known primary key, as suggested in Get the number of rows in table using SQLAlchemy.

Query for just a single known column:
session.query(MyTable.col1).count()

I managed to render the following SELECT with SQLAlchemy on both layers.
SELECT count(*) AS count_1
FROM "table"
Usage from the SQL Expression layer
from sqlalchemy import select, func, Integer, Table, Column, MetaData
metadata = MetaData()
table = Table("table", metadata,
Column('primary_key', Integer),
Column('other_column', Integer) # just to illustrate
)
print select([func.count()]).select_from(table)
Usage from the ORM layer
You just subclass Query (you have probably anyway) and provide a specialized count() method, like this one.
from sqlalchemy.sql.expression import func
class BaseQuery(Query):
def count_star(self):
count_query = (self.statement.with_only_columns([func.count()])
.order_by(None))
return self.session.execute(count_query).scalar()
Please note that order_by(None) resets the ordering of the query, which is irrelevant to the counting.
Using this method you can have a count(*) on any ORM Query, that will honor all the filter andjoin conditions already specified.

I needed to do a count of a very complex query with many joins. I was using the joins as filters, so I only wanted to know the count of the actual objects. count() was insufficient, but I found the answer in the docs here:
http://docs.sqlalchemy.org/en/latest/orm/tutorial.html
The code would look something like this (to count user objects):
from sqlalchemy import func
session.query(func.count(User.id)).scalar()

Addition to the Usage from the ORM layer in the accepted answer: count(*) can be done for ORM using the query.with_entities(func.count()), like this:
session.query(MyModel).with_entities(func.count()).scalar()
It can also be used in more complex cases, when we have joins and filters - the important thing here is to place with_entities after joins, otherwise SQLAlchemy could raise the Don't know how to join error.
For example:
we have User model (id, name) and Song model (id, title, genre)
we have user-song data - the UserSong model (user_id, song_id, is_liked) where user_id + song_id is a primary key)
We want to get a number of user's liked rock songs:
SELECT count(*)
FROM user_song
JOIN song ON user_song.song_id = song.id
WHERE user_song.user_id = %(user_id)
AND user_song.is_liked IS 1
AND song.genre = 'rock'
This query can be generated in a following way:
user_id = 1
query = session.query(UserSong)
query = query.join(Song, Song.id == UserSong.song_id)
query = query.filter(
and_(
UserSong.user_id == user_id,
UserSong.is_liked.is_(True),
Song.genre == 'rock'
)
)
# Note: important to place `with_entities` after the join
query = query.with_entities(func.count())
liked_count = query.scalar()
Complete example is here.

If you are using the SQL Expression Style approach there is another way to construct the count statement if you already have your table object.
Preparations to get the table object. There are also different ways.
import sqlalchemy
database_engine = sqlalchemy.create_engine("connection string")
# Populate existing database via reflection into sqlalchemy objects
database_metadata = sqlalchemy.MetaData()
database_metadata.reflect(bind=database_engine)
table_object = database_metadata.tables.get("table_name") # This is just for illustration how to get the table_object
Issuing the count query on the table_object
query = table_object.count()
# This will produce something like, where id is a primary key column in "table_name" automatically selected by sqlalchemy
# 'SELECT count(table_name.id) AS tbl_row_count FROM table_name'
count_result = database_engine.scalar(query)

I'm not clear on what you mean by "without explicitly asking for it with execute()" So this might be exactly what you are not asking for.
OTOH, this might help others.
You can just run the textual SQL:
your_query="""
SELECT count(*) from table
"""
the_count = session.execute(text(your_query)).scalar()

def test_query(val: str):
query = f"select count(*) from table where col1='{val}'"
rtn = database_engine.query(query)
cnt = rtn.one().count
but you can find the way if you checked debug watch

query = session.query(table.column).filter().with_entities(func.count(table.column.distinct()))
count = query.scalar()
this worked for me.
Gives the query:
SELECT count(DISTINCT table.column) AS count_1
FROM table where ...

Below is the way to find the count of any query.
aliased_query = alias(query)
db.session.query(func.count('*')).select_from(aliased_query).scalar()
Here is the link to the reference document if you want to explore more options or read details.