Develop Reference

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.

PRIMARY KEY must be unique

I am trying to write some data to a table in a database which I am creating.
However, I am facing with an integrity error like:
sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) PRIMARY KEY must be unique
My question is how to avoid these errors as I will run a couple of times the script

Basically you are creating an object with an already existing primary key, and it's not accepted by SQLite. Verify it by querying the db with something like
select * from airport where id = 6256
If the query returns a result, you need to change the id of the airport you are saving. Since you use the autoincrement, you don't need to specify an id and the DBMS will assign the next free id in that table.

Error: Duplicate foreign key constraint name

I exported a schema from workbench and now trying to use that script to create table in my server, But getting error
I tried to change the table and also tried to find duplicate foriegn key.
ERROR 1826: Duplicate foreign key constraint name 'bank_id'
SQL Statement:
-- Table aditya.users_has_bank
CREATE TABLE IF NOT EXISTS `aditya`.`users_has_bank` (
`users_user_id` INT NOT NULL AUTO_INCREMENT,
`bank_id` INT NOT NULL,
`user_id` INT NOT NULL,
PRIMARY KEY (`users_user_id`),
INDEX `bank_id_idx` (`bank_id` ASC) VISIBLE,
INDEX `user_id_idx` (`user_id` ASC) VISIBLE,
CONSTRAINT `bank_id`
FOREIGN KEY (`bank_id`)
REFERENCES `aditya`.`bank` (`bank_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `user_id`
FOREIGN KEY (`user_id`)
REFERENCES `aditya`.`users` (`user_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB

High possibility that FK name is used in other tables within your schema. Please do practice good FK naming convention
Source: Foreign Key naming scheme

Python/ Django Key already exists. Postgres

I Have a project built in django and it uses a postgres database.
This database was populated by CSVs files. So when I want to insert a new object I got the error "duplicated key" because the object with id = 1 already exists.
The code :
user = User(name= "Foo")
user.save()
The table users has the PK on the id.
Indexes:
"users_pkey" PRIMARY KEY, btree (id)
If I get the table's details in psql I got:
Column| Type | Modifiers
------+-------- +--------------------------------------
id | integer | not null default nextval('users_id_seq'::regclass)
Additionally, if I do user.dict after create the variable user and before saving it, I get 'id': None
How can I save the user with an id that is not being used?

You most likely inserted your Users from the CSV setting the id value explicitly, when this happens the postgres sequence is not updated and as a result of that when you try to add a new user the sequence generates an already used value
Check this other question for reference postgres autoincrement not updated on explicit id inserts
The solution is what the answer for that question says, update your sequence manually

You can fix it by setting users_id_seq manually.
SELECT setval('users_id_seq', (SELECT MAX(id) from "users"));

Unless you have name as a primary key for the table the above insert should work. If you have name as primary key remove it and try it.

In Postgres SQL you can specify id as serial and you can mark it as Primary Key.Then whenever you will insert record , it will be in a sequence.
i.e id serial NOT NULL and
CONSTRAINT primkey PRIMARY KEY (id).
As you said its a pre populated by CSV , so when you insert it from python code it will automatically go the end of the table and there will be no duplicate values.

Set SQLAlchemy to use PostgreSQL SERIAL for identity generation

Background:
The application I am currently developing is in transition from SQLite3 to PostgreSQL. All the data has been successfully migrated, using the .dump from the current database, changing all the tables of the type
CREATE TABLE foo (
id INTEGER NOT NULL,
bar INTEGER,
...
PRIMARY KEY (id),
FOREIGN KEY(bar) REFERENCES foobar (id),
...
);
to
CREATE TABLE foo (
id SERIAL NOT NULL,
bar INTEGER,
...
PRIMARY KEY (id),
FOREIGN KEY(bar) REFERENCES foobar (id) DEFERRABLE,
...
);
and SET CONSTRAINTS ALL DEFERRED;.
Since I am using SQLAlchemy I was expecting things to work smoothly from then on, after of course changing the engine. But the problem seems to be with the autoincrement of the primary key to a unique value on INSERT.
The table, say foo, I am currently having trouble with has 7500+ rows but the sequence foo_id_seq's current value is set on 5(because I have tried the inserts five times now all of which have failed).
Question:
So now my question is that without explicitly supplying the id, in the INSERT statement, how can I make Postgres automatically assign a unique value to the id field if foo? Or more specifically, have the sequence return a unique value for it?
Sugar:
Achieve all that through the SQLAlchemy interface.
Environment details:
Python 2.6
SQLAlchemy 8.2
PostgreSQL 9.2
psycopg2 - 2.5.1 (dt dec pq3 ext)
PS: If anybody finds a more appropriate title for this question please edit it.

Your PRIMARY KEY should be defined to use a SEQUENCE as a DEFAULT, either via the SERIAL convenience pseudo-type:
CREATE TABLE blah (
id serial primary key,
...
);
or an explicit SEQUENCE:
CREATE SEQUENCE blah_id_seq;
CREATE TABLE blah (
id integer primary key default nextval('blah_id_seq'),
...
);
ALTER SEQUENCE blah_id_seq OWNED BY blah.id;
This is discussed in the SQLAlchemy documentation.
You can add this to an existing table:
CREATE SEQUENCE blah_id_seq OWNED BY blah.id;
ALTER TABLE blah ALTER COLUMN id SET DEFAULT nextval('blah_id_seq');
if you prefer to restore a dump then add sequences manually.
If there's existing data you've loaded directly into the tables with COPY or similar, you need to set the sequence starting point:
SELECT setval('blah_id_seq', max(id)+1) FROM blah;
I'd say the issue is likely to be to do with your developing in SQLite, then doing a dump and restoring that dump to PostgreSQL. SQLAlchemy expects to create the schema its self with the appropriate defaults and sequences.
What I recommend you do instead is to get SQLAlchemy to create a new, empty database. Dump the data for each table from the SQLite DB to CSV, then COPY that data into the PostgreSQL tables. Finally, update the sequences with setval so they generate the appropriate values.
One way or the other, you will need to make sure that the appropriate sequences are created. You can do it by SERIAL pseudo-column types, or by manual SEQUENCE creation and DEFAULT setting, but you must do it. Otherwise there's no way to assign a generated ID to the table in an efficient, concurrency-safe way.

Use
alter sequence foo_id_seq restart with 7600
should give you 7601 next time you call the sequence.
http://www.postgresql.org/docs/current/static/sql-altersequence.html
And then subsequent values. Just make sure that you restart it with a value > the last id.