Is there a way to get a list of tables that have one-on-one relationship to a given table in SQLite3?
For example, here table ab has a one-on-one relationship with both table abc and abd. Is there a query or queries to return abc and abd for the given table name ab?
-- By default foreign key is diabled in SQLite3
PRAGMA foreign_keys = ON;
CREATE TABLE a (
aid INTEGER PRIMARY KEY
);
CREATE TABLE b (
bid INTEGER PRIMARY KEY
);
CREATE TABLE ab (
aid INTEGER,
bid INTEGER,
PRIMARY KEY (aid, bid)
FOREIGN KEY (aid) REFERENCES a(aid)
FOREIGN KEY (bid) REFERENCES b(bid)
);
-- tables 'ab' and 'abc' have a one-on-one relationship
CREATE TABLE abc (
aid INTEGER,
bid INTEGER,
name TEXT NOT NULL,
PRIMARY KEY (aid, bid) FOREIGN KEY (aid, bid) REFERENCES ab(aid, bid)
);
-- tables 'ab' and 'abd' have a one-on-one relationship
CREATE TABLE abd (
aid INTEGER,
bid INTEGER,
value INTEGER CHECK( value > 0 ),
PRIMARY KEY (aid, bid) FOREIGN KEY (aid, bid) REFERENCES ab(aid, bid)
);
CREATE TABLE w (
id INTEGER PRIMARY KEY
);
The following tedious precedure may get me the list of tables I want:
Get primary keys for table ab:
SELECT l.name FROM pragma_table_info('ab') as l WHERE l.pk > 0;
get foreign keys for other tables (this case is for table abd):
SELECT * from pragma_foreign_key_list('abd');
Do parsing to get what the list of tables of one-on-one relationships.
However, there must exist a more elegant way, I hope.
For SQL Server, there are sys.foreign_keys and referenced_object_id avaible (see post). Maybe there is something similar to that in SQLite?
Edit: adding two more tables for test
-- tables 'ab' and 'abe' have a one-on-one relationship
CREATE TABLE abe (
aid INTEGER,
bid INTEGER,
value INTEGER CHECK( value < 0 ),
PRIMARY KEY (aid, bid) FOREIGN KEY (aid, bid) REFERENCES ab
);
-- tables 'ab' and 'abf' have a one-on-one relationship
CREATE TABLE abf (
aidQ INTEGER,
bidQ INTEGER,
value INTEGER,
PRIMARY KEY (aidQ, bidQ) FOREIGN KEY (aidQ, bidQ) REFERENCES ab(aid, bid)
);
Edit: verify FK for table abe
sqlite> PRAGMA foreign_keys;
1
sqlite> .schema abe
CREATE TABLE abe (
aid INTEGER,
bid INTEGER,
value INTEGER CHECK( value < 0 ),
PRIMARY KEY (aid, bid) FOREIGN KEY (aid, bid) REFERENCES ab
);
sqlite> DELETE FROM abe;
sqlite> INSERT INTO abe (aid, bid, value) VALUES (2, 1, -21);
sqlite> INSERT INTO abe (aid, bid, value) VALUES (-2, 1, -21);
Error: FOREIGN KEY constraint failed
sqlite> SELECT * FROM ab;
1|1
1|2
2|1
Alternative
Although not a single query solution the following only requires submission/execution of a series of queries and is therefore platform independent.
It revolves around using two tables:-
a working copy of sqlite_master
a working table to store the the output of SELECT pragma_foreign_key_list(?)
Both tables are created via a CREATE-SELECT, although neither has any rows copied, so the tables are empty.
A trigger is applied to the working copy of sqlite_master to insert into the table that stores the result of SELECT pragma_foreign_key_list(table_name_from_insert);
The relevant rows are copied from sqlite_master via a SELECT INSERT and thus the triggering populates the store table.
The following is the testing code :-
DROP TABLE IF EXISTS fklist;
DROP TABLE IF EXISTS master_copy;
DROP TRIGGER IF EXISTS load_fklist;
/* Working version of foreign_key_list to store ALL results of SELECT pragma_foreign_key_list invocation */
CREATE TABLE IF NOT EXISTS fklist AS SELECT '' AS child,*
FROM pragma_foreign_key_list((SELECT name FROM sqlite_master WHERE type = 'not a type' LIMIT 1));
/* Working version of sqlite master */
CREATE TABLE IF NOT EXISTS master_copy AS SELECT * FROM sqlite_master WHERE type = 'not a type';
/* Add an after insert trigger for master copy to add to fklist */
CREATE TRIGGER IF NOT EXISTS load_fklist
AFTER INSERT ON master_copy
BEGIN
INSERT INTO fklist SELECT new.name,* FROM pragma_foreign_key_list(new.name);
END
;
/* Populate master_copy from sqlite_master (relevant rows)
and thus build the fklist
*/
INSERT INTO master_copy SELECT *
FROM sqlite_master
WHERE type = 'table'
AND instr(sql,' REFERENCES ') > 0
;
SELECT * FROM fklist;
DROP TABLE IF EXISTS fklist;
DROP TABLE IF EXISTS master_copy;
DROP TRIGGER IF EXISTS load_fklist;
Using a similar test base as per the previous answer the above results in :-
Is there a way to get a list of tables that have one-on-one relationship to a given table in SQLite3?
Not with certainty as coding a Foreign Key constraint does not define a relationship (rather it supports a relationship), that is relationships can exists without a FK constraint.
A Foreign Key constraint defines:-
a) a rule that enforces referential integrity
b) optionally maintains/alters referential integrity when the referred to column is changed (ON DELETE and ON UPDATE )
As such looking at the Foreign Key List only tells you where/if a FK constraint has been coded.
Saying that the following will get the tables with the constraint and the referenced tables.
More elegant is a matter of opinion, so it's up to you :-
WITH cte_part(name,reqd,rest) AS (
SELECT name,'',substr(sql,instr(sql,' REFERENCES ') + 12)||' REFERENCES '
FROM sqlite_master
WHERE sql LIKE '% REFERENCES %(%'
UNION ALL
SELECT
name,
substr(rest,0,instr(rest,' REFERENCES ')),
substr(rest,instr(rest,' REFERENCES ') + 12)
FROM cte_part
WHERE length(rest) > 12
)
SELECT DISTINCT
CASE
WHEN length(reqd) < 1 THEN name
ELSE
CASE substr(reqd,1,1)
WHEN '''' THEN substr(replace(reqd,substr(reqd,1,1),''),1,instr(reqd,'(')-3)
WHEN '[' THEN substr(replace(replace(reqd,'[',''),']',''),1,instr(reqd,'(')-3)
WHEN '`' THEN substr(replace(reqd,substr(reqd,1,1),''),1,instr(reqd,'(')-3)
ELSE substr(reqd,1,instr(reqd,'(')-1)
END
END AS tablename
FROM cte_part
;
As an example of it's use/results :-
screenshot from Navicat
Here's an adaptation of the above that includes, where appropriate, the child table that references the parent :-
WITH cte_part(name,reqd,rest) AS (
SELECT name,'',substr(sql,instr(sql,' REFERENCES ') + 12)||' REFERENCES '
FROM sqlite_master
WHERE sql LIKE '% REFERENCES %(%'
UNION ALL
SELECT
name,
substr(rest,0,instr(rest,' REFERENCES ')),
substr(rest,instr(rest,' REFERENCES ') + 12)
FROM cte_part
WHERE length(rest) > 12
)
SELECT DISTINCT
CASE
WHEN length(reqd) < 1 THEN name
ELSE
CASE substr(reqd,1,1)
WHEN '''' THEN substr(replace(reqd,substr(reqd,1,1),''),1,instr(reqd,'(')-3)
WHEN '[' THEN substr(replace(replace(reqd,'[',''),']',''),1,instr(reqd,'(')-3)
WHEN '`' THEN substr(replace(reqd,substr(reqd,1,1),''),1,instr(reqd,'(')-3)
ELSE substr(reqd,1,instr(reqd,'(')-1)
END
END AS tablename,
CASE WHEN length(reqd) < 1 THEN '' ELSE name END AS referrer
FROM cte_part
;
Example of the Result :-
the artists table is referenced by albums as the SQL used to create the albums table is CREATE TABLE 'albums'([AlbumId] INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL ,[Title] TEXT NOT NULL ,[ArtistId] INTEGER NOT NULL , FOREIGN KEY ([ArtistId]) REFERENCES 'artists'([ArtistId]))
i.e. FOREIGN KEY ([ArtistId]) REFERENCES 'artists'([ArtistId]))
the employees table is self-referencing as per CREATE TABLE 'employees'(.... REFERENCES 'employees'([EmployeeId]))
Additional re comment:-
(I am still trying to understand your code...)
The code is based upon selecting rows from sqlite_master where the row is for a table (type = 'table'), as opposed to an index, trigger or view and where the sql column contains the word REFERENCES with a space before and after and there is a following left parenthesis.
The last condition used to weed out the likes of CREATE TABLE oops (`REFERENCES` TEXT, `x REFERENCES Y`);
For each selected row 3 columns are output:-
name which is the name of the table as extracted from the name column of sqlite_master,
reqd is initially an empty string (i.e. initial)
rest the rest of sql that follows the referred to table name with suffixed with REFERENCES.
The UNION ALL adds rows that are built upon what is newly added to the CTE, i.e. the three columns are extracted as per :-
name is the name
reqd is the sql from the rest column up until the first REFERENCES term (i.e. the table and referenced column(s))
rest is the sql from after the REFERENCES term
As with any recursion the end needs to be detected, this is when the entire sql statement has been reduced to being less than 12 (i.e the length of " REFERENCES ", the term used for splitting the sql statement).
This is what is termed as a RECURSIVE CTE
Finally the resultant CTE is then queried. If the reqd field is empty then the tablename column is the name column otherwise (i.e. the reqd column contains data(part of the sql)) the table name is extracted (part up to left parenthesis if not enclosed (`,' or [ with ])) or extracted from between the enclosure.
The following is what the final query results in if all the CTE columns are included (some data has been truncated):-
As can clearly be seen the extracted sql progressively reduces
The answer is intended as in-principle and has not been extensively tested to consider all scenarios, it may well need tailoring.
I have encountered this situation where i plan to insert a generated column which the expression (the expression to design quoted in (???..I need this suggestion expression too..???) schema table below. the output is a calculation depend on the value of broker_id and place to generated column name brokage.
Your sharing and guidance on the scenario is much appreciated.
Thank you and warm regards
new sqlite learner.
sqlite> .schema buy
CREATE TABLE buy(
buy_id INTEGER,
stock_id INTEGER,
investor_id INTEGER,
broker_id INTEGER,
unit INTEGER,
price REAL,
date TEXT,
cost REAL GENERATED ALWAYS AS (unit*price),
brokage REAL GENERATED ALWAYS AS (??? depend on broker_id for expression ???),
PRIMARY KEY (buy_id, stock_id, investor_id, broker_id),
FOREIGN KEY (stock_id) REFERENCES stock(stock_id) ON DELETE CASCADE ON UPDATE NO ACTION,
FOREIGN KEY (investor_id) REFERENCES stock(investor_id) ON DELETE CASCADE ON UPDATE NO ACTION
FOREIGN KEY (broker_id) REFERENCES stock(broker_id) ON DELETE CASCADE ON UPDATE NO ACTION
);
sqlite> .mode column
sqlite> .header on
sqlite> SELECT * FROM buy;
buy_id stock_id investor_id broker_id unit price date cost brokage
------ -------- ----------- --------- ----- ----- ---------- ------ --------
1 7 1 1 2000 0.68 2020-06-24 1360.0
2 25 1 3 2000 0.88 2020-10-22 1760.0
You can do it with a CASE expression:
CREATE TABLE buy(
buy_id INTEGER,
stock_id INTEGER,
investor_id INTEGER,
broker_id INTEGER,
unit INTEGER,
price REAL,
date TEXT,
cost REAL GENERATED ALWAYS AS (unit*price),
brokage REAL GENERATED ALWAYS AS (CASE broker_id WHEN 1 THEN 9 WHEN 3 THEN 28 END),
PRIMARY KEY (buy_id, stock_id, investor_id, broker_id),
FOREIGN KEY (stock_id) REFERENCES stock(stock_id) ON DELETE CASCADE ON UPDATE NO ACTION,
FOREIGN KEY (investor_id) REFERENCES stock(investor_id) ON DELETE CASCADE ON UPDATE NO ACTION
FOREIGN KEY (broker_id) REFERENCES stock(broker_id) ON DELETE CASCADE ON UPDATE NO ACTION
);
Consider the following table definition:
CREATE TABLE names (
id INTEGER,
name TEXT NOT NULL,
PRIMARY KEY (id)
)
Does it guarantee that the id will be auto-incremented for every new insert AND that the values for deleted rows will not be reused?
I looked up in the documentation for Sqlite3, but couldn't find the answer.
id INTEGER PRIMARY KEY on it's own guarantees (requires) a unique integer value and will if no value is specifically assigned provide one until the highest value has reached the highest allowed value for a 64 bit signed integer (9223372036854775807) after which an unused value may be found and applied.
With AUTOINCREMENT there is a guarantee (if not circumvented) of always providing a higher value BUT if 9223372036854775807 is reached instead of allocating an unused number an SQLITE_FULL error will result. That is the only difference from the point of view of what number will be assigned.
Neither guarantees a monotonically increasing value.
Without AUTOINCREMENT the calculation/algorithm is equivalent to
1 + max(rowid) and if the value is greater than 9223372036854775807 an attempt is made to find an unused and therefore lower value.
I've not seen that anyone has come across the situation where a random unused value has not been assigned.
With AUTOINCREMENT the calculation/algorithim is
the greater of 1 + max(rowid) or SELECT seq FROM sqlite_sequence WHERE name = 'the_table_name_the_rowid_is_being_assigned_to' and if the value is greater than 9223372036854775807 then SQLITE_FULL ERROR.
noting that either way there is the possibility that the max rowid is for a row that eventually doesn't get inserted and therefore the potential for gaps.
The answer is perhaps best put as: it's best/recommended to use the id column solely for it's intended purpose, that of efficiently identifying a row and not as a means of handling other data requirements, and if done so, there there is no need for AUTOINCREMENT (which has overheads)
In short
Does it guarantee that the id will be auto-incremented
NO
values for deleted rows will not be reused?
NO for the given code
for :-
CREATE TABLE names (id INTEGER PRIMARY KEY AUTOINCREMENT name TEXT NOT NULL)
again NO as if 9223372036854775807 is reached then an SQLITE_FULL error will result, otherwise YES.
So really AUTOINCREMENT is only really relevant (if the id used as expected/intended) when the 9223372036854775807'th row has been inserted.
Perhaps consider the following :-
DROP TABLE IF EXISTS table1;
DROP TABLE IF EXISTS table2;
CREATE TABLE IF NOT EXISTS table1 (id INTEGER PRIMARY KEY, somecolumn TEXT);
CREATE TABLE IF NOT EXISTS table2 (id INTEGER PRIMARY KEY AUTOINCREMENT, somecolumn TEXT);
INSERT INTO table1 VALUES (9223372036854775807,'blah');
INSERT INTO table2 VALUES (9223372036854775807,'blah');
INSERT INTO table1 (somecolumn) VALUES(1),(2),(3);
SELECT * FROM table1;
INSERT INTO table2 (somecolumn) VALUES(1),(2),(3);
This creates the two similar tables, the only difference being the use of AUTOINCREMENT. Each has a row inserted with the highest allowable value for the id column.
An attempt is then made to insert 3 rows where the id will be assigned by SQLite.
3 rows are inserted into the table without AUTOINCREMENT but no rows are inserted when AUTOINCREMENT is used. as per :-
CREATE TABLE IF NOT EXISTS table1 (id INTEGER PRIMARY KEY, somecolumn TEXT)
> OK
> Time: 0.098s
CREATE TABLE IF NOT EXISTS table2 (id INTEGER PRIMARY KEY AUTOINCREMENT, somecolumn TEXT)
> OK
> Time: 0.098s
INSERT INTO table1 VALUES (9223372036854775807,'blah')
> Affected rows: 1
> Time: 0.094s
INSERT INTO table2 VALUES (9223372036854775807,'blah')
> Affected rows: 1
> Time: 0.09s
INSERT INTO table1 (somecolumn) VALUES(1),(2),(3)
> Affected rows: 3
> Time: 0.087s
SELECT * FROM table1
> OK
> Time: 0s
INSERT INTO table2 (somecolumn) VALUES(1),(2),(3)
> database or disk is full
> Time: 0s
The result of the SELECT for table1 (which may differ due to randomness) was :-
Did anyone work on react native expo's sqlite database with foreign key constraints? Can we use structure similar to sql?
I'm trying to work on it building multiple tables with foreign key condition.
Example: If we have 2 tables Persons and Orders where personID is referred as foreign key in orders table. How would it be done using sqlite?
You would have two tables, perhaps with a column as the alias of the rowid column, this
e.g.
CREATE TABLE persons (
personid INTEGER PRIMARY KEY,
personname TEXT
);
CREATE TABLE orders (
orderid INTEGER PRIMARY KEY,
ordername TEXT,
person_reference INTEGER REFERENCES persons(personid)
);
Note that you have to turn foreign key handling on e.g. by executing PRAGMA foreign_keys = ON; (or true). See PRAGMA foreign_keys
in SQLite coding column_name INTEGER PRIMARY KEY defines that column as an alias of the rowid column, and if a value is not provided for the column when inserting then an integer value will be assigned. The initial value for the first row will be 1, subsequent values will typically be 1 greater than the highest rowid value (read the link above in regards why the word typically has been used).
If you then try to insert an Order for a non-existent personid you will then get a Foreign Key conflict.
An alternative to the column level definition would be to define the foreign key(s) at the table level e.g.
CREATE TABLE orders (
orderid INTEGER PRIMARY KEY,
ordername TEXT,
person_reference INTEGER,
FOREIGN KEY (person_reference) REFERENCES persons(personid)
);
As an example, consider the following :-
INSERT INTO persons (personname) VALUES
('Fred'),
('Mary'),
('Sue'),
('Tom')
;
INSERT INTO orders (ordername, person_reference) VALUES
('Order 1 for Fred',1),
('Order 2 for Sue',3),
('Order 3 for Fred',1),
('Order 4 for Mary',2)
;
INSERT into orders (ordername, person_reference) VALUES
('Order 5 for nobody',100);
The result would be :-
INSERT INTO persons (personname) VALUES ('Fred'),('Mary'),('Sue'),('Tom')
> Affected rows: 4
> Time: 0.453s
INSERT INTO orders (ordername, person_reference) VALUES
('Order 1 for Fred',1),('Order 2 for Sue',3),('Order 3 for Fred',1),('Order 4 for Mary',2)
> Affected rows: 4
> Time: 0.084s
INSERT into orders (ordername, person_reference) VALUES
('Order 5 for nobody',100)
> FOREIGN KEY constraint failed
> Time: 0s
i.e. the last as there is no row in the persons table with a personid of 100, then the last insert (on it's own doe demonstration) fails.
You may wish to refer to SQLite Foreign Key Support
I have the following SQLite table:
CREATE TABLE podcast_search (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
search TEXT NOT NULL UNIQUE
)
Whenever a user inserts/updates a row in the table, I want to sort that row at the end of the table. Thus, if I insert the following values:
_id | search | sort
===================
1 | foo | 1
2 | bar | 2
3 | quiz | 3
And then later update the 1 row from foo to foo2, the values should look like:
_id | search | sort
===================
2 | bar | 2
3 | quiz | 3
1 | foo2 | 4
I've implemented this thusly:
CREATE TABLE podcast_search (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
search TEXT NOT NULL UNIQUE,
update_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
)
CREATE TRIGGER update_date_update_trigger
AFTER UPDATE ON podcast_search FOR EACH ROW
BEGIN
UPDATE podcast_search
SET update_date = CURRENT_TIMESTAMP
WHERE _id = OLD._id;
END
However, my unit tests require a 1000ms sleep between insert/update operations in order to reliably sort, and this amount of delay is very annoying for unit testing.
I thought I could implement a vector clock instead, but it seems that AUTOINCREMENT values only exist for primary key columns. Does SQLite offer any other AUTOINCREMENT or AUTOINCREMENT-like option?
I'm running this on Android P, but this should be a generic SQLite problem.
UPDATE
I'm now using an sort INTEGER NOT NULL UNIQUE column, and SELECT-ing the largest row in that column and manually incrementing it before an INSERT/UPDATE:
CREATE TABLE podcast_search (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
search TEXT NOT NULL UNIQUE,
sort INTEGER NOT NULL UNIQUE
)
SELECT sort from podcast_search ORDER BY sort DESC
either increment sort in application code, or set it to 0
Could I do this in a TRIGGER instead?
I thought I could implement a vector clock instead, but it seems that
AUTOINCREMENT values only exist for primary key columns. Does SQLite
offer any other AUTOINCREMENT or AUTOINCREMENT-like option?
They are not in fact AUTOINCREMENT values rather a column with AUTOINCREMENT will be an alias of the rowid column; not because AUTOINCREMENT has been coded but because INTEGER PRIMARY KEY has been coded.
All coding AUTOINCREMENT does is add a constraint that an auto-generated value MUST be greater than any other existing or used value. This only in fact becomes apparent if when a rowid with the value of 9223372036854775807 exists. In which case an attempt to insert a new row with an auto-generated rowid (i.e. no value is specified for the rowid column or an alias thereof) will result in an SQLITE_FULL error.
Without AUTOINCREMENT and when the highest rowid is 9223372036854775807 (the highest possible value for a rowid) an attempt is made to use a free value, which would obviously be lower than 9223372036854775807.
SQLite Autoincrement
You may wish to note the very first line of the linked page which says :-
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 can't see any need from your description.
So what you want is a means of assigning a value for the column that is to be sorted that is 1 greater than the highest current value for that column, so it becomes the latest for sorting purposes, a subquery that retrieves max(the_column) + 1 would do what you wish. This could be in an UPDATE, TRIGGER or in an INSERT.
rowid = max(rowid) + 1 is basically how SQLite assigns a value to rowid unless AUTOINCREMENT is used when 1 is added to the greater of max(rowid) and the value, for the respective table, obtained from the table sqlite_sequence (will only exist if AUTOINCREMENT is used). It is referencing and maintaining sqlite_sequence that incurs the penalties.
For example you could use the following (which eliminates the need for an additional column and the additional index) :-
-- SETUP THE DATA FOR TESTING
DROP TABLE IF EXISTS podcast_searchv1;
CREATE TABLE IF NOT EXISTS podcast_searchv1 (
_id INTEGER NOT NULL PRIMARY KEY,
search TEXT NOT NULL UNIQUE
);
INSERT INTO podcast_searchv1 (search)
VALUES('foo'),('bar'),('guide')
;
-- Show original data
SELECT * FROM podcast_searchv1;
-- DO THE UPDATE
UPDATE podcast_searchv1 SET search = 'new value', _id = (SELECT max(_id) + 1 FROM podcast_searchv1) WHERE search = 'foo';
-- Show the changed data
SELECT * FROM podcast_searchv1;
The results being :-
and then :-