To what I've learned so far, SQlite stores all data "as is" into any column regardless of the column declaration. The affinity only matters upon reading, am I correct? If so, would it be a big deal implementing ALTER TABLE ALTER COLUMN?
----- Original Message ----- From: Dan Kennedy <danielk1...@gmail.com> To: sqlite-users@mailinglists.sqlite.org <sqlite-users@mailinglists.sqlite.org> Sent: Friday, November 23, 2018, 16:30:12 Subject: [sqlite] Bug?: unexpected behaviour - alter parent table in a deferred foreign key relationship On 11/23/2018 09:54 PM, szmate1618 wrote: > Dear list members, > I have the following problem, with which I'd like to request your aid: > Currently, at version 3.25.2, SQLite only has a limited support for alter > table. E.g. you cannot change the datatype (type affinity) of a column, or > drop a column. > The usual workaround is to create a new table with the desired schema, fill > it with data from the original table, drop the original table, and rename > the new one. But what if the original table is a parent table in a foreign > key relationship? > The official solution > <https://www.sqlite.org/lang_altertable.html#otheralter> is turning foreign > keys off, making the changes you want, then turning foreign keys on. But > I'm slightly annoyed this cannot be done in a transaction (because these > PRAGMA > foreign_keys =s don't take effect inside of transactions, so they need to > be issued before and after). "PRAGMA foreign_keys = ?" is a property of the connection only, not the database file. So what advantage would there be in including the PRAGMA statements in the body of a transaction? Dan. > I'd like to use deferred foreign keys instead. I have 3 queries, one of > them seems to work, the two others do not. My questions are the following: > - Does the seemingly working query work by design? Or it's just a > fortunate(?) constellation of multiple factors, and depending on other > tables or new data in the database it might break in the future? Somewhat > like undefined behavior in C++? > - Why do the other ones not work? How are they different from the first > one? > Setup > PRAGMA foreign_keys = OFF; > DROP TABLE IF EXISTS Parent;CREATE TABLE Parent(A TEXT UNIQUE, > COLUMN_TO_DROP FLOAT);INSERT INTO Parent VALUES('whatever', 0.0); > DROP TABLE IF EXISTS Child;CREATE TABLE Child(C TEXT REFERENCES > Parent(A) DEFERRABLE INITIALLY DEFERRED);INSERT INTO Child > VALUES('whatever'); > PRAGMA foreign_keys = ON; > Query1 - seems to be working as intended > BEGIN TRANSACTION;CREATE TABLE Temp AS SELECT A FROM Parent;DROP TABLE > Parent;CREATE TABLE Parent (A TEXT UNIQUE);INSERT INTO Parent SELECT * > FROM Temp;DROP TABLE Temp;COMMIT; > Query2 - create [...] as select [...] fails > BEGIN TRANSACTION;CREATE TABLE Temp AS SELECT A FROM Parent;DROP TABLE > Parent;CREATE TABLE Parent AS SELECT * FROM Temp; -- different > from Query1CREATE UNIQUE INDEX ParentIndex on Parent(A); -- different > from Query1DROP TABLE Temp;COMMIT; > Result: > sqlite> PRAGMA foreign_key_check; > sqlite> .schemaCREATE TABLE Child(C TEXT REFERENCES Parent(A) > DEFERRABLE INITIALLY DEFERRED);CREATE TABLE Parent(A TEXT);CREATE > UNIQUE INDEX ParentIndex on Parent(A); > sqlite> SELECT * FROM Parent; > whatever > Query3 - insert into [...] fails > BEGIN TRANSACTION;CREATE TABLE Temp (A TEXT UNIQUE); -- different > from Query1INSERT INTO Temp SELECT A FROM Parent; -- different from > Query1DROP TABLE Parent;CREATE TABLE Parent (A TEXT UNIQUE);INSERT > INTO Parent SELECT * FROM Temp;DROP TABLE Temp;COMMIT; > Result: > sqlite> PRAGMA foreign_key_check; > sqlite> .schemaCREATE TABLE Child(C TEXT REFERENCES Parent(A) > DEFERRABLE INITIALLY DEFERRED);CREATE TABLE Parent (A TEXT UNIQUE); > sqlite> SELECT * FROM Parent; > whatever > Note that PRAGMA foreign_key_check does not report any problem in any of > the cases. > I posted an identical question on StackOverflow, but no one was able to > provide any information so far. Thanks in advance! > Máté Szabó > _______________________________________________ > sqlite-users mailing list > sqlite-users@mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
