Develop Reference

Composite Primary Key and autoincremented ID

I am trying to build a composite primary key for my tabels. They should also have a self incremented id. My problem is that when I use a composite primary key the ID becomes NULL (as seen in the pictures)
here it works as it should but no composite key
here the id is NULL no matter what.
I tried different synatxes and also key words like NOT NULL and AUTOINCREMENT but nothing seems to work.
Here is the code without composite key
mystr = "CREATE TABLE IF NOT EXISTS KM%s(id INTEGER PRIMARY KEY, date TEXT, client INTEGER)"%(month.replace('-',"))
print(mystr)
c.execute(mystr) #create a table
conn.commit()'''
Here is the code with COMPOSITE KEY
mystr = "CREATE TABLE IF NOT EXISTS KM%s(id INTEGER, date TEXT, client INTEGER, primary key (id, client)"%(month.replace('-',"))
print(mystr)
c.execute(mystr) #create a table
conn.commit()

I was sure that I'd used autoincremented integer columns in the past which were not primary keys, but it certainly doesn't work today with SQLite.
I must echo what #forpas has already said in the comment that you just can't do that.
The solution would be to add the UNIQUE constraint to id and generate your ID programmatically as you go. You do not need to track your current maximum ID because you can simply ask SQLite what the max is:
SELECT MAX(id) FROM KM<month>;
Increment that value by 1 and include it in your INSERT INTO statement.
I'd like to offer a couple of tips:
Using two integers as your composite key is a bad idea. Take composite key 1315 for example. Is that client 315 with an ID of 1, client 15 with an ID of 13, or client 5 with an ID of 131? It's true that primary keys are just for searching and do not have to be unique in many cases, but using integers generally does not work well.
The second tip is not to create a new database table for each month. A very good rule is that identically-structured tables should be combined into a single table. In this case you would add a column called month (actually, it would be 'date' then you would search by month) and keep everything in one table, not one table per month.

Creating a table in database defining a column as primary key

I am creating a database from different CSV files. After doing this I have tried to define the primary key table by table but I got an error.
c.execute("ALTER TABLE patient_data ADD PRIMARY KEY (ID);").fetchall()
OperationalError: near "PRIMARY": syntax error
Maybe the best thing to avoid this error is to define the primary key when the table is create but I dont know how to do that. I have been working with python for a few years but today is my first approach with SQL.
This is the code I use to import a CSV to a table
c.execute('''DROP TABLE IF EXISTS patient_data''')
c.execute(''' CREATE TABLE patient_data (ID, NHS_Number,Full_Name,Gender, Birthdate, Ethnicity, Postcode)''')
patients_admitted.to_sql('patient_data', conn, if_exists='append', index = False)
c.execute('''SELECT * FROM patient_data''').fetchall()

This is too long for a comment.
If your table does not have data, just re-create it with the primary key definition.
If your table does have data, you cannot add a primary key in one statement. Why not? The default value is either NULL or constant. And neither is allowed as a primary key.
And finally, SQLite does not allow you to add a primary key to an existing table. The solution is to copy the data to another table, recreate the table with the structure you want, and then copy the data back in.

Combine CREATE TABLE, ADD COLUMNS, PRIMARY KEY, AS SELECT, and WHERE into one operation

I need to create a copy of a table (if it does not already exist), and this copy needs one of the existing columns to become a primary key.
Currently I have the following SQL commands (in a Python script):
CREATE TABLE IF NOT EXISTS FilteredTable AS SELECT * FROM RawTable WHERE <cond>
ALTER TABLE FilteredTable ADD COLUMN IF NOT EXISTS (NewCol1 TEXT, etc TEXT)
ALTER TABLE FilteredTable ADD PRIMARY KEY (ColumnNameFromRaw)
This works fine the first time around, but of course when run again after the table already exists it complains that a primary key already exists. Is there a way to combine the ADD PRIMARY KEY with the CREATE TABLE ... command so that it only attempts to set the primary key when the table needs to be created?
EDIT
Python code can be used.
SQL: 10.1.23-MariaDB
Python: 2.7

You can add extra columns and indexes in the CREATE TABLE command even when coming from a SELECT. So do it all in one step:
CREATE TABLE IF NOT EXISTS FilteredTable (
NewCol1 TEXT, etc TEXT,
PRIMARY KEY (ColumnNameFromRaw)
) AS SELECT * FROM RawTable WHERE <cond>
Note: the column names are matched up by name. That is, if * has a NewCol1, it will go into that TEXT column. If not, then NewCol1 will be empty.

This isn't quite as clean as a purely SQL solution, but it works in the event that you're accessing SQL indirectly like so...
# ...
# (New table creation)
# ...
# Display column data for specified table
curs.execute("SHOW COLUMNS FROM NewTable")
# Collect the data as a tuple of tuples containing chart rows
colsNew = curs.fetchall()
# Iterate through each table column (row in the chart)
for col in colsNew:
# Check to see if Key is not "PRI" for the Field (Column) "DesiredColumn"
if (col[0] == "DesiredColumn") and (col[3] != "PRI"):
# Make DesiredColumn the primary key
curs.execute("ALTER TABLE NewTable ADD PRIMARY KEY (DesiredColumn)")

How to get the last row id on update?

I am a beginner in mysql and may be its my fault somewhere, and not able to understand how this can be resolved.
This is structure of my table:-
CREATE TABLE `nearest_product_type` (
`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY,
`created` datetime NOT NULL,
`modified` datetime NOT NULL,
`name` varchar(15) NOT NULL UNIQUE
)
;
And this is the code i am trying:-
base = MySQLdb.connect (host="localhost", user = "root", passwd = "sheeshmohsin", db="points")
basecursor = base.cursor()
queryone = """INSERT INTO nearest_product_type (name,created,modified) VALUES (%s,%s,%s) ON DUPLICATE KEY UPDATE name=name """
category = "Indica"
valueone = (category,datetime.datetime.now(),datetime.datetime.now())
basecursor.execute(queryone, valueone)
product_id = basecursor.lastrowid
basecursor.close()
base.commit()
base.close()
print product_id
On running this python script, first time when category is not unique, it works fine, but on running again with the same category as first time, last row id returns 0. but i need the id of the last row which is updated.
And when i checked the rows in table, the auto-increment is also working, suppose if i run the script four times, in first time when category is unique the id is 1 and suppose another unique category comes in fourth time, then the id assigned to this row is 4, but it should be 2, because its second row. how can i solve this?

The ON DUPLICATE KEY UPDATE part here will not work as the key is the auto-increment column, which will never get duplicates.
It is almost certainly this clause that is causing the unexpected counts, particularly given the UNIQUE setting on name.
You can try using something like SELECT MAX(id) FROM nearest_product_type to get the last id added.

Something is wrong in the way you access the database. When you try to insert an new row in your database with a name that already exists, as the column name is declared to be unique, the insert will fail.
If you want to modify an existing row , you must use an UPDATE statement not an INSERT one. And there's nothing in SQL to do an insert or update.
And nothing in autoincrement guarantees that id are consecutive. All you know is that the database will allow a different id for each inserted row, but insertion failure can (and do in you case) result is holes is the id sequence.
Furthermore, some drivers may allow for pre-reservation of ids, particurarly with network connections to allow a client connection to get a bunch of ids in case it would insert more than one row. It that case, if another client asks for ids, and both clients insert rows alternatively, the id will not follow the insertion time.

creating blank field and receving the INTEGER PRIMARY KEY with sqlite, python

I am using sqlite with python. When i insert into table A i need to feed it an ID from table B. So what i wanted to do is insert default data into B, grab the id (which is auto increment) and use it in table A. Whats the best way receive the key from the table i just inserted into?

As Christian said, sqlite3_last_insert_rowid() is what you want... but that's the C level API, and you're using the Python DB-API bindings for SQLite.
It looks like the cursor method lastrowid will do what you want (search for 'lastrowid' in the documentation for more information). Insert your row with cursor.execute( ... ), then do something like lastid = cursor.lastrowid to check the last ID inserted.
That you say you need "an" ID worries me, though... it doesn't matter which ID you have? Unless you are using the data just inserted into B for something, in which case you need that row ID, your database structure is seriously screwed up if you just need any old row ID for table B.

Check out sqlite3_last_insert_rowid() -- it's probably what you're looking for:
Each entry in an SQLite table has a
unique 64-bit signed integer key
called the "rowid". The rowid is
always available as an undeclared
column named ROWID, OID, or _ROWID_ as
long as those names are not also used
by explicitly declared columns. If the
table has a column of type INTEGER
PRIMARY KEY then that column is
another alias for the rowid.
This routine returns the rowid of the
most recent successful INSERT into the
database from the database connection
in the first argument. If no
successful INSERTs have ever occurred
on that database connection, zero is
returned.
Hope it helps! (More info on ROWID is available here and here.)

Simply use:
SELECT last_insert_rowid();
However, if you have multiple connections writing to the database, you might not get back the key that you expect.