I'm new to sqlite and sql in gerneral so I don't know if my approach is reasonable.
I want to model inventory items that can be created, lent, returned and discarded.
I want to model this using two tables, one for items, containing an id, a name and a reference to the last transaction (created, lent, returned, ...) and a table of transactions containing an id transaction type, date, and a reference to the item.
Since creating only one table leaves the database in an inconsitent state with one table referencing a non existant table I thought of using a transaction to crate both tables at once, and defining the foreign keys as deferrable. Creation of a new item would have to be done together in one transaction with creating a "created" event to leave the database in a consistent state.
The following code gives me the error Query Error: not an error Unable to execute multiple statements at a time in sqliteman on linux.
PRAGMA foreign_keys = ON;
begin transaction;
create table items (
id integer primary key,
name char(30),
foreign key (last_transaction) references transactions(transaction_id) DEFERRABLE INITIALLY DEFERRED
);
create table transactions(
transaction_id integer primary key,
text char(100)
foreign key (item) references items(id) DEFERRABLE INITIALLY DEFERRED
);
commit transaction;
Does my approach make sense at all?
If yes, why does the code not work? (Did I make a mistake somewhere, or is what I'm trying impossible in mysql?)
Note: simply creating the tables in one transaction without the foreign key constraints gives the same error. (Could this be a similar Problem to: this question)
Related
For example, let say DB has foreign key A.b_id -> B.id with SET NULL on delete.
If record with some B.id get deleted, all b_id references will be set to NULL.
But if A already contains record where A.b_id has value that is not in B.id (it was inserted without foreign keys support), is there a way to force SQLite DB check foreign keys and set to NULL such data?
In fact, in first place I'm solving an DB upgrading task.
On start app checks if internal DB (resource) has higher version than user DB.
If so it backups user DB, copies internal empty DB to user storage. Than turns off foreign keys support and fills new DB with data from backup, inserting automatically in loop table by table for all columns with same name. Turns on foreign keys support back.
Everything works fine, but if in some table in old DB there is no foreign key constrain previously, while new DB has one, the data will be inserted as is and link can point nowhere (possibly wrong links is unavoidable and not related to question).
Yes, I understand a way to insert without turning off foreign keys support, but it would need knowledge of tables dependencies order that I would like to avoid.
Thanks for any help in advance!
Although I don't know of a way that automatically will set to NULL all orphaned values of a column in a table that (should) reference another column in another table, there is a way to get a report of all these cases and then act accordingly.
This is the PRAGMA statement foreign_key_check:
PRAGMA schema.foreign_key_check;
or for a single table check:
PRAGMA schema.foreign_key_check(table-name);
From the documenation:
The foreign_key_check pragma checks the database, or the table called
"table-name", for foreign key constraints that are violated. The
foreign_key_check pragma returns one row output for each foreign key
violation. There are four columns in each result row. The first column
is the name of the table that contains the REFERENCES clause. The
second column is the rowid of the row that contains the invalid
REFERENCES clause, or NULL if the child table is a WITHOUT ROWID
table. The third column is the name of the table that is referred to.
The fourth column is the index of the specific foreign key constraint
that failed. The fourth column in the output of the foreign_key_check
pragma is the same integer as the first column in the output of the
foreign_key_list pragma. When a "table-name" is specified, the only
foreign key constraints checked are those created by REFERENCES
clauses in the CREATE TABLE statement for table-name.
Check a simplified demo of the way to use this PRAGMA statement, or its function counterpart pragma_foreign_key_check().
You can get a list of the rowids of all the problematic rows of each table.
In your case, you can execute an UPDATE statement that will set to NULL all the orphaned b_ids:
UPDATE A
SET b_id = NULL
WHERE rowid IN (SELECT rowid FROM pragma_foreign_key_check() WHERE "table" = 'A')
This also works in later versions of SQLite:
UPDATE A
SET b_id = NULL
WHERE rowid IN (SELECT rowid FROM pragma_foreign_key_check('A'))
but it does not seem to work up to SQLite 3.27.0
I have to create a table with autoincrement column. I am creating an web app with sqlite as a background and sql alchemy is the orm layer.Python and Flask as front end. I am creating some department list and department id should be auto incremented.When I try to add department through UI I dont provide department id.Because department id is the primary key and should be auto incremented.I have added the department name and department jobs through UI without any error.But when I try to list the departments list I am getting error.
AttributeError: 'NoneType' object has no attribute 'department_id'
What I tried is,My sqlite
create table Departments(department_id primarykey integer autoincrement,department_name char,department_jobs char);
When I try creating this schema I am getting an error called 'syntax error near autoincrement'
I tried by using capital letter,auto_increment,auto increment.
Nothing is working
My sql alchemy looks like this
class Departments(db.Model):
"Adding the department"
department_id = db.Column(db.Integer,primary_key=True)
department_name = db.Column(db.String(50),nullable=False)
department_jobs = db.Column(db.String(40),nullable=False)
What I am expecting here is how do I do the auto incrementin sqllite and sqlalchemy so that I can use it in both frontend and backend.
You have coded PRIMARYKEY instead of PRIMARY KEY and you should also code INTEGER PRIMARY KEY as the column type should appear first.
There is no need, from your explanation, to code AUTOINCREMENT.
Not using AUTOINCREMENT will be more efficient and will as far as you are concerned do the same thing. i.e. if the value for the department_id is not supplied, then SQLite will automatically generate a value which will be 1 for the first row that is inserted and then typically 1 greater for the next row and so on (SQLite does not guarantee montonically increasing numbers).
SQLite Autoincrement which includes
The AUTOINCREMENT keyword imposes extra CPU, memory, disk space, and disk I/O overhead and should be avoided if not strictly needed. It is usually not needed.
I'd sugggest just using :-
create table Departments(department_id INTEGER PRIMARY KEY,department_name char,department_jobs char);
I am attempting to use foreign key support in SQLite to maintain referential integrity on a single-table database that has a reflexive join.
e.g.
PRAGMA foreign_keys = ON;
create table tree (
objectId text unique not null,
parentObjectID text,
foreign key (parentObjectID) references tree(parentObjectID) on delete cascade
)
The behavior that I am hoping for is that when a parent row is deleted, its children and their children are deleted as well.
However, when I attempt to delete the root row (where the expected behavior would be that every other row in the database is also deleted), I get this error:
sqlite> delete from tree where objectid = '0';
Error: foreign key mismatch
Are my expectations out of whack with with SQLite foreign key support (and delete behaviors) can provide?
Your problem is pretty simple, your FK on parentObjectId references parentObjectId rather than objectId and SQLite doesn't detect this bit of confusion until you try to use the table. If your FK is defined like this:
foreign key (parentObjectID) references tree(objectID) on delete cascade
From the fine manual:
So, in other words, misconfigured foreign key constraints that require looking at both the child and parent are DML errors. The English language error message for foreign key DML errors is usually "foreign key mismatch" but can also be "no such table" if the parent table does not exist. Foreign key DML errors are may be reported if:
The parent table does not exist, or
The parent key columns named in the foreign key constraint do not exist, or
The parent key columns named in the foreign key constraint are not the primary key of the parent table and are not subject to a unique
constraint using collating sequence specified in the CREATE TABLE, or
The child table references the primary key of the parent without specifying the primary key columns and the number of primary key
columns in the parent do not match the number of child key columns.
The third point would seem to apply here since parentObjectId is neither a PK nor constrained to be unique so that's why you don't see an error until you try to modify the table's content (i.e. use a DML statement rather than a DDL statement).
I have a bunch of SQLite db files, and I need to merge them into one big db files.
How can I do that?
Added
Based on this, I guess those three commands should merge two db into one.
attach './abc2.db' as toMerge;
insert into test select * from toMerge.test
detach database toMerge
The problem is the db has PRIMARY KEY field, and I got this message - "Error: PRIMARY KEY must be unique".
This is the test table for the db.
CREATE TABLE test (id integer PRIMARY KEY AUTOINCREMENT,value text,goody text)
I'm just thinking off my head here... (and probably after everybody else has moved on, too).
Mapping the primary key to "NULL" should yield the wanted result (no good if you use it as foreign key somewhere else, since the key probably exists, but has different contents)
attach './abc2.db' as toMerge;
insert into test select NULL, value, goody from toMerge.test;
detach database toMerge;
actual test:
sqlite> insert into test select * from toMerge.test;
Error: PRIMARY KEY must be unique
sqlite> insert into test select NULL, value, goody from toMerge.test;
sqlite> detach database toMerge;
I'm not 100% sure, but it seems that I should read all the elements and insert the element (except the PRIMARY KEY) one by one into the new data base.
I know that SQLite does not enforce foreign keys natively, but that's not my primary concern. The question is: If I declare
CREATE TABLE invoice (
invoiceID INTEGER PRIMARY KEY,
clientID INTEGER REFERENCES client(clientID),
...
)
will sqlite at least use the information that clientID is a foreign key to optimize queries and automatically index invoice.clientID, or is this constraint a real no-op?
In the SQLite Documentation it says:
... "an index should be created on the child key columns of each foreign key constraint"
ie. the index is not automatically created, but you should create one in every instance.
Even if it is not actually a no-op (a data structure describing the constraint is added to the table), foreign key related statement doesn't create any index on involved columns.
Indexes are implicitly created only in the case of PRIMARY KEY and UNIQUE statements.
For more details, check it out build.c module on the sqlite source tree:
http://www.sqlite.org/cvstrac/rlog?f=sqlite/src/build.c https://www.sqlite.org/src/file?name=src/build.c&ci=tip