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.

Why does SQLite insert duplicate composite primary keys?

Code:
import sqlite3
c = sqlite3.Connection(':memory:')
c.execute('CREATE TABLE foo(a INTEGER, b VARCHAR(8), PRIMARY KEY(a, b))')
c.execute('INSERT INTO foo(a) VALUES (1)')
c.execute('INSERT INTO foo(a) VALUES (1)')
print(c.execute('SELECT * FROM foo').fetchall())
Output:
[(1, None), (1, None)]
Why is SQLite inserting rows with duplicate primary keys? How do I fix this?

SQL PK (PRIMARY KEY) means UNIQUE NOT NULL. You shouldn't expect to be able to have a NULL in a value for a PK, let alone only one. You should declare PK columns NOT NULL and not put NULL in them.
SQL As Understood By SQLite:
Each row in a table with a primary key must have a unique combination of values in its primary key columns. For the purposes of determining the uniqueness of primary key values, NULL values are considered distinct from all other values, including other NULLs. If an INSERT or UPDATE statement attempts to modify the table content so that two or more rows have identical primary key values, that is a constraint violation.
According to the SQL standard, PRIMARY KEY should always imply NOT NULL. Unfortunately, due to a bug in some early versions, this is not the case in SQLite. Unless the column is an INTEGER PRIMARY KEY or the table is a WITHOUT ROWID table or the column is declared NOT NULL, SQLite allows NULL values in a PRIMARY KEY column. SQLite could be fixed to conform to the standard, but doing so might break legacy applications. Hence, it has been decided to merely document the fact that SQLite allowing NULLs in most PRIMARY KEY columns.
Since NULL in a PK is against SQL, it seems moot what SQLite then chooses to do when constraining and manipulating tables with NULLs in a PK. But it uses the usual SQL interpretation that NULL is not equal to NULL for purposes of UNIQUE. This is like when you declare a column set UNIQUE NULL. So as a constraint, SQLite PK is a synonym for UNIQUE instead of UNIQUE NOT NULL.
A UNIQUE constraint is similar to a PRIMARY KEY constraint, except that a single table may have any number of UNIQUE constraints. For each UNIQUE constraint on the table, each row must contain a unique combination of values in the columns identified by the UNIQUE constraint. For the purposes of UNIQUE constraints, NULL values are considered distinct from all other values, including other NULLs.

SQLite, like many other SQL databases, considers two NULLs as different values for the purposes of uniqueness (partially because, in SQL, NULL == NULL is false).
I don't believe there is a way to alter this behavior. As a workaround, you can use an empty string in column b as "no value".

How do I copy Unique constraint in Oracle with SQLAlchemy?

I have a table (on which I have no control) that I must copy. The target schema can be the same as the original one, so all indexes and constraints have to be defined without a name, implicitly.
I'm using Python 3.4.3 with SQLAlchemy 1.0.8 and cx_oracle 5.2.
The table is like this:
CREATE TABLE "MY_TABLE"
( "ITEMID" NUMBER(*,0) NOT NULL ENABLE,
"LABEL" NVARCHAR2(80) NOT NULL ENABLE,
"FIRSTCHILDID" NUMBER(*,0) NOT NULL ENABLE,
"LASTCHILDID" NUMBER(*,0) NOT NULL ENABLE,
"DEFAULTPARENTID" NUMBER(*,0) NOT NULL ENABLE,
"PICTUREID" NUMBER(6,0) NOT NULL ENABLE,
"SECURITYID" NUMBER(*,0) NOT NULL ENABLE,
PRIMARY KEY ("ITEMID")
UNIQUE ("LABEL"));
The code I'm using is at https://gist.github.com/toyg/9fb541ff3dbc8c175329 but the core of it is this (smeta and dmeta are source and target Metadata, bound):
table = Table(table_name, smeta, autoload=True)
target_name = prefix + str(table.name)
target_table = table.tometadata(dmeta, name=target_name)
for constraint in target_table.constraints:
constraint.name = None
target_table.metadata.create_all(dengine)
It fails with this error:
sqlalchemy.exc.DatabaseError: (cx_Oracle.DatabaseError)
ORA-00955: name is already used by an existing object
[SQL: b'CREATE UNIQUE INDEX sys_c009016 ON "TMP_MY_TABLE" (label)']
This is because SQLAlchemy is trying to create the Unique index after creating the table, when it's already too late: CREATE INDEX requires a name, so SA uses the same name as the existing one, and it fails.
I tried setting the index name to None before creation, to give SA a hint, but that results in errors because it expects a string there at all times.
Is there any way to tell SA to just append the bloody UNIQUE clause to the table DDL right away?

"UNIQUE INDEX" means that the Index construct is used. Its DDL is not emitted within the CREATE TABLE. It sounds like you are looking for a UniqueConstraint construct. It seems likely that in this case, Oracle returns reflected information about what you first created as a UniqueConstraint object as an Index object with unique=True (these constructs are "different", but on many backends they are synonymous and/or mixed and matched and sometimes even mirrored, it's totally confusing).
at the end of the day if you want the UNIQUE keyword as an inline constraint you need to use the UniqueConstraint object, and you'd need to remove this Index from the table - you might be able to get away with table.indexes.remove(index). The Index object wouldn't be in table.constraints. You probably want to do your "copy" of the table in a more programmatic way rather than using tometadata(). Look perhaps into using the inspection interface directly and just build the Table you want from that.

sqlite3 prints without explicit command

I'm trying to get a rowid if a data row exists. What I have now is
row_id = self.dbc.cursor.execute("SELECT ROWID FROM Names where unq_id=?",(namesrow['unq_id'],)).fetchall()[0][0]
where namesrow is a dictionary of column names with corresponding data to fill into the table. The problem is this prints 'unq_id' when runs and I'm not sure how to get rid of it.
I'm using sqlite3 and python. Any help's appreciated!

quoting the sqlite documentation:
With one exception noted below, if a rowid table has a primary key
that consists of a single column and the declared type of that column
is "INTEGER" in any mixture of upper and lower case, then the column
becomes an alias for the rowid.
So if your unq_id is the integer primary key in this table, then rowid and unq_id will be the same field.

Sqlite insert not working with python

I'm working with sqlite3 on python 2.7 and I am facing a problem with a many-to-many relationship. I have a table from which I am fetching its primary key like this
current.execute("SELECT ExtensionID FROM tblExtensionLookup where ExtensionName = ?",[ext])
and then i am fetching another primary key from another table
current.execute("SELECT HostID FROM tblHostLookup where HostName = ?",[host])
now what i am doing is i have a third table with these two keys as foreign keys and i inserted them like this
current.execute("INSERT INTO tblExtensionHistory VALUES(?,?)",[Hid,Eid])
The problem is i don't know why but the last insertion is not working it keeps giving errors. Now what i have tried is:
First I thought it was because I have an autoincrement primary id for the last mapping table which I didn't provide, but isn't it supposed to consider itself as it's auto incremented? However I went ahead and tried adding Null,None,0 but nothing works.
Secondly I thought maybe because i'm not getting the values from tables above so I tried printing it out and it shows so it works.
Any suggestions what I am doing wrong here?
EDIT :
When i don't provide primary key i get error as
The table has three columns but you provided only two values
and when i do provide them as None,Null or 0 it says
Parameter 0 is not supported probably because of unsupported type
I tried implementing the #abarnet way but still keeps saying parameter 0 not supported
connection = sqlite3.connect('WebInfrastructureScan.db')
with connection:
current = connection.cursor()
current.execute("SELECT ExtensionID FROM tblExtensionLookup where ExtensionName = ?",[ext])
Eid = current.fetchone()
print Eid
current.execute("SELECT HostID FROM tblHostLookup where HostName = ?",[host])
Hid = current.fetchone()
print Hid
current.execute("INSERT INTO tblExtensionHistory(HostID,ExtensionID) VALUES(?,?)",[Hid,Eid])
EDIT 2 :
The database schema is :
table 1:
CREATE TABLE tblHostLookup (
HostID INTEGER PRIMARY KEY AUTOINCREMENT,
HostName TEXT);
table2:
CREATE TABLE tblExtensionLookup (
ExtensionID INTEGER PRIMARY KEY AUTOINCREMENT,
ExtensionName TEXT);
table3:
CREATE TABLE tblExtensionHistory (
ExtensionHistoryID INTEGER PRIMARY KEY AUTOINCREMENT,
HostID INTEGER,
FOREIGN KEY(HostID) REFERENCES tblHostLookup(HostID),
ExtensionID INTEGER,
FOREIGN KEY(ExtensionID) REFERENCES tblExtensionLookup(ExtensionID));

It's hard to be sure without full details, but I think I can guess the problem.
If you use the INSERT statement without column names, the values must exactly match the columns as given in the schema. You can't skip over any of them.*
The right way to fix this is to just use the column names in your INSERT statement. Something like:
current.execute("INSERT INTO tblExtensionHistory (HostID, ExtensionID) VALUES (?,?)",
[Hid, Eid])
Now you can skip any columns you want (as long as they're autoincrement, nullable, or otherwise skippable, of course), or provide them in any order you want.
For your second problem, you're trying to pass in rows as if they were single values. You can't do that. From your code:
Eid = current.fetchone()
This will return something like:
[3]
And then you try to bind that to the ExtensionID column, which gives you an error.
In the future, you may want to try to write and debug the SQL statements in the sqlite3 command-line tool and/or your favorite GUI database manager (there's a simple extension that runs in for Firefox if you don't want anything fancy) and get them right, before you try getting the Python right.
* This is not true with all databases. For example, in MSJET/Access, you must skip over autoincrement columns. See the SQLite documentation for how SQLite interprets INSERT with no column names, or similar documentation for other databases.