I'm creating a WebSQL table in Chrome with the following statement:
'CREATE TABLE IF NOT EXISTS recs(id, fname,lname,email,country,comments, synced integer,PRIMARY KEY(id))'
Inserting records does not appear to be creating primary keys. How should one go about creating unique keys in webSQL?
Use the unique keyword and check for the constraint error to verify.
'CREATE TABLE IF NOT EXISTS recs (id unique, fname, lname)'
Related
So i am trying to complete finance. Following is the .schema:
sqlite> .schema
CREATE TABLE users (id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, username TEXT NOT NULL, hash TEXT NOT NULL, cash NUMERIC NOT NULL DEFAULT 10000.00);
CREATE TABLE sqlite_sequence(name,seq);
CREATE TABLE history(
symbol TEXT, name TEXT, shares INTEGER, price NUMERIC, time DATETIME
);
CREATE UNIQUE INDEX username ON users (username);
When i try to add foriegn key to history table it always return error. Here is my code:
sqlite> ALTER TABLE history ADD COLUMN id INT;
sqlite> ALTER TABLE history ADD FOREIGN KEY(id) REFRENCES users(id);
Parse error: near "FOREIGN": syntax error
ALTER TABLE history ADD FOREIGN KEY(id) REFRENCES users(id);
^--- error here
I think based on what I see in the sqlite docs that the statement should be together with the ADD column:
ALTER TABLE history ADD COLUMN id INTEGER REFERENCES users(id);
But you please check me on this syntax! Another option is to take care of creating the constraint at the same time that you create the table.
CREATE TABLE history(
symbol TEXT,
name TEXT,
shares INTEGER,
price NUMERIC,
time DATETIME,
id INTEGER,
FOREIGN KEY (id)
REFERENCES users (id));
It might not be something you have realized (yet) but every database has its unique flavor of SQL, so despite there being a SQL standard there are often little differences in the syntax of SQL for specific db implementations. So you always have to beware of this when looking up commands for your sql db.
Further detail on Sqlite foreign key constraints can be found here:
https://www.sqlitetutorial.net/sqlite-foreign-key/
Does SQLite indeed have a limitation that it is not possible to retrieve the name of a foreign key? I am asking because I couldn't find this limitation mentioned anywhere in their documentation.
For example, I run the following script:
CREATE TABLE
users (
id INTEGER NOT NULL PRIMARY KEY,
first_name TEXT NOT NULL,
last_name TEXT NOT NULL
) ;
CREATE TABLE
orders (
id INTEGER NOT NULL PRIMARY KEY,
user_id INTEGER NOT NULL,
CONSTRAINT fk_users FOREIGN KEY (user_id) REFERENCES users(id)
) ;
Now I would like to check that the key "fk_users" was created indeed, so I run the following PRAGMA:
PRAGMA foreign_key_list(orders);
I would expect to see the name of my foreign key in the first column, but I am seeing some "0" value instead. Moreover, if I create multiple foreign keys with custom names, they are all called either "0" or "1".
Is this indeed a limitation of SQLite, or am I missing something?
There is no mechanism to extract the constraint name.
The table sqlite_master stores a CREATE command in the column "sql". You could query that command and do some parsing to extract the name of the foreign key. An example for a combined foreign key that works for me:
SELECT sql FROM sqlite_master WHERE name = 'song'
yields
CREATE TABLE "song" (
"songid" INTEGER,
"songartist" TEXT,
"songalbum" TEXT,
"songname" TEXT,
CONSTRAINT "fk__song_album" FOREIGN KEY ("songartist", "songalbum") REFERENCES "album" ("albumartist", "albumname")
)
and contains the name "fk__song_album" of the foreign key.
If one alters the foreign key with a query, the content of the sql column is modified/updated:
The text in the sqlite_master.sql column is a copy of the original CREATE statement text that created the object, except normalized as described above and as modified by subsequent ALTER TABLE statements. The sqlite_master.sql is NULL for the internal indexes that are automatically created by UNIQUE or PRIMARY KEY constraints.
https://www.sqlite.org/fileformat2.html
Extra tip:
In order to see the foreign key information in Navicat (Lite) ... right click on a table and choose "Design table". Then select the foreign keys tab.
Recently I started using SQLite (as required for my study) and I came accross a couple of restrictions of SQLite and I was wondering: can't SQLite create foreign keys on the same table? E.g. this is my code:
CREATE TABLE Categories
(
name varchar(20),
parent_category varchar(20) NULL,
PRIMARY KEY(name),
FOREIGN KEY parent_category_fk(parent_category) REFERENCES Categories(name)
)
But it gives me an error for the foreign key when I try to execute the SQL in SQLiteStudio.
Does anyone know why this isn't working?
The problem is that you have the wrong syntax for the FK clause. It should be:
FOREIGN KEY (parent_category) REFERENCES Categories(name)
If you want to name the FK constraint, you do that with a prefix of the CONSTRAINT keyword, like this:
CONSTRAINT parent_category_fk FOREIGN KEY (parent_category) REFERENCES Categories(name)
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