Getting SQLite DELETE LIKE result [duplicate] - c++

Question

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Return deleted rows in sqlite
(3 answers)
Closed 3 years ago.
I want to delete several rows from a table by using DELETE LIKE query in C++. I know how to do it and it works. But also I want to know which rows were actually deleted. Is there a way to do it via 1 query or it is impossible and the only way to do it is
1. SELECT LIKE
2. DELETE LIKE

Answer 1

As alternative to SELECT -> DELETE you could also use a TRIGGER.
The following example shows/demonstrates a relatively generic way (a little inefficient as such) for both :-
DROP TABLE IF EXISTS mytable;
DROP TABLE IF EXISTS mytable_deletions;
DROP TABLE IF EXISTS mytable_deletions2;
DROP TRIGGER IF EXISTS mytable_deletions_trigger;
/* MAIN TABLE */
CREATE TABLE IF NOT EXISTS mytable(id INTEGER PRIMARY KEY, mydata TEXT);
/* CREATE TABLES TO RECORD DELETIONS (first for 1. select->delete the other for 2. trigger)*/
/* Note that these are created based upon the source table, with an additional column srowid so as to be able to definitively delete rows (extra column may not be needed) */
CREATE /*TEMP option? */ TABLE IF NOT EXISTS mytable_deletions AS SELECT 0 AS srowid,* FROM mytable WHERE mydata <> mydata;
CREATE /*TEMP option? */ TABLE IF NOT EXISTS mytable_deletions2 AS SELECT 0 AS srowid,* FROM mytable WHERE mydata <> mydata;
/* Create the BEFORE DELETE Trigger */
CREATE TRIGGER IF NOT EXISTS mytable_deletions_trigger BEFORE DELETE ON mytable
BEGIN
INSERT INTO mytable_deletions2 SELECT rowid AS srowid,* FROM mytable WHERE rowid = old.rowid;
END
;
/* LOAD TESTING DATA */
INSERT INTO mytable (mydata) VALUES('A'),('B'),('C'),('D'),('E');
/* CLEAR PREVIOUS DELETIONS */
DELETE FROM mytable_deletions;
DELETE FROM mytable_deletions2;
/* 1. RECORD DELETIONS PRIOR AND DELETE ACCORDING TO RECORDED DELETIONS */
INSERT INTO mytable_deletions SELECT rowid AS srowid,* FROM mytable WHERE mydata >= 'C';
/* DO THE ACTUAL DELETIONS (will fire trigger 2.) */
DELETE FROM mytable WHERE rowid IN (SELECT srowid FROM mytable_deletions);
/* Display results from TRIGGER */
SELECT * FROM mytable;
SELECT * FROM mytable_deletions;
SELECT * FROM mytable_deletions2;
/* CLEANUP */
DROP TABLE IF EXISTS mytable;
DROP TABLE IF EXISTS mytable_deletions;
DROP TABLE IF EXISTS mytable_deletions2;
DROP TRIGGER IF EXISTS mytable_deletions_trigger;
Running the above results in :-
Remaining data :-
Deleted Rows (select->delete)
Deleted Rows (trigger)