Selectively ignoring tuples from a table - mysql

Question

The problem that we are tackling with a data mining application is best described with an illustrative example.
There is a sample table myTable, which is defined as follows:
CREATE TABLE myTable
(
id INT UNSIGNED AUTO_INCREMENT,
colA VARCHAR(8),
colB VARCHAR(12),
revFlag CHAR(8), -- 'REVISED' or any other value, including NULL
PRIMARY KEY(id)
);
Any tuple with a revFlag value of REVISED takes precedence over any other tuple with the same value for colA, as long as the revFlag value of the latter tuple is not REVISED. In other words when we select rows from the table we skip all rows for which the revFlag value is not REVISED and there exists a row with the same value for colA for which the revFlag value is REVISED.
We populate the table as follows:
INSERT INTO myTable(colA, colB) VALUES ('XSR0KA3V', 'OLD-O7RAR81X'),
('4F2JG71O', 'OLD-E71BE63L'), ('MML3HN48', 'OLD-B02PFB63'),
('5H0MWVSB', 'OLD-V70XLGHT'), ('JW73ZX0J', 'OLD-KME1GXQF'),
('XZV0EY0G', 'OLD-N06BURDF'), ('9HBQZ88V', 'OLD-76HSPUAL'),
('YI5AT6G4', 'OLD-X8KAWD7Z');
INSERT INTO myTable(colA, colB, revFlag) VALUES
('XSR0KA3V', 'NEW-O7RAR81X', 'REVISED'),
('MML3HN48', 'NEW-B02PFB63', 'REVISED'),
('9HBQZ88V', 'NEW-76HSPUAL', 'REVISED'),
('YI5AT6G4', 'NEW-X8KAWD7Z', 'XYZ'),
('Z8H2B5KY', '3RINJV0K', 'REVISED');
Naturally SELECT * FROM myTable yields the following:
+----+----------+--------------+---------+
| id | colA | colB | revFlag |
+----+----------+--------------+---------+
| 1 | XSR0KA3V | OLD-O7RAR81X | NULL |
| 2 | 4F2JG71O | OLD-E71BE63L | NULL |
| 3 | MML3HN48 | OLD-B02PFB63 | NULL |
| 4 | 5H0MWVSB | OLD-V70XLGHT | NULL |
| 5 | JW73ZX0J | OLD-KME1GXQF | NULL |
| 6 | XZV0EY0G | OLD-N06BURDF | NULL |
| 7 | 9HBQZ88V | OLD-76HSPUAL | NULL |
| 8 | YI5AT6G4 | OLD-X8KAWD7Z | NULL |
| 9 | XSR0KA3V | NEW-O7RAR81X | REVISED |
| 10 | MML3HN48 | NEW-B02PFB63 | REVISED |
| 11 | 9HBQZ88V | NEW-76HSPUAL | REVISED |
| 12 | YI5AT6G4 | NEW-X8KAWD7Z | XYZ |
| 13 | Z8H2B5KY | 3RINJV0K | REVISED |
+----+----------+--------------+---------+
We would like to design a query that does not return any tuples that are REVISED by other tuples. In our case the output should look like this:
+----+----------+--------------+---------+
| id | colA | colB | revFlag |
+----+----------+--------------+---------+
| 2 | 4F2JG71O | OLD-E71BE63L | NULL |
| 4 | 5H0MWVSB | OLD-V70XLGHT | NULL |
| 5 | JW73ZX0J | OLD-KME1GXQF | NULL |
| 6 | XZV0EY0G | OLD-N06BURDF | NULL |
| 8 | YI5AT6G4 | OLD-X8KAWD7Z | NULL |
| 9 | XSR0KA3V | NEW-O7RAR81X | REVISED |
| 10 | MML3HN48 | NEW-B02PFB63 | REVISED |
| 11 | 9HBQZ88V | NEW-76HSPUAL | REVISED |
| 12 | YI5AT6G4 | NEW-X8KAWD7Z | XYZ |
| 13 | Z8H2B5KY | 3RINJV0K | REVISED |
+----+----------+--------------+---------+

Answer 1

You can use a NOT EXISTS clause to filter out all rows for which another row exists which has the same colA value and revFlag = 'REVISED':
SELECT *
FROM myTable t1
WHERE NOT EXISTS (
SELECT *
FROM myTable t2
WHERE t2.id != t1.id AND t2.colA = t1.colA AND t2.revFlag = 'REVISED'
)
Output:
id colA colB revFlag
2 4F2JG71O OLD-E71BE63L (null)
4 5H0MWVSB OLD-V70XLGHT (null)
5 JW73ZX0J OLD-KME1GXQF (null)
6 XZV0EY0G OLD-N06BURDF (null)
8 YI5AT6G4 OLD-X8KAWD7Z (null)
9 XSR0KA3V NEW-O7RAR81X REVISED
10 MML3HN48 NEW-B02PFB63 REVISED
11 9HBQZ88V NEW-76HSPUAL REVISED
12 YI5AT6G4 NEW-X8KAWD7Z XYZ
13 Z8H2B5KY 3RINJV0K REVISED
Demo on dbfiddle

Answer 2

SELECT stuff
FROM somewhere x
LEFT
JOIN somewhere y
ON y.thing = x.thing
AND y.otherthing = x.otherthing
AND y.anotherthing > x.anotherthing
AND y.whatever = 'some value'
WHERE y.anotherthing .... ;

Answer 3

You could use the IN Clause
Schema (MySQL v8.0)
CREATE TABLE table1 (
`id` INTEGER,
`colA` VARCHAR(8),
`colB` VARCHAR(12),
`revFlag` VARCHAR(7)
);
INSERT INTO table1
(`id`, `colA`, `colB`, `revFlag`)
VALUES
('1', 'XSR0KA3V', 'OLD-O7RAR81X', NULL),
('2', '4F2JG71O', 'OLD-E71BE63L', NULL),
('3', 'MML3HN48', 'OLD-B02PFB63', NULL),
('4', '5H0MWVSB', 'OLD-V70XLGHT', NULL),
('5', 'JW73ZX0J', 'OLD-KME1GXQF', NULL),
('6', 'XZV0EY0G', 'OLD-N06BURDF', NULL),
('7', '9HBQZ88V', 'OLD-76HSPUAL', NULL),
('8', 'YI5AT6G4', 'OLD-X8KAWD7Z', NULL),
('9', 'XSR0KA3V', 'NEW-O7RAR81X', 'REVISED'),
('18', 'XSR0KA3V', 'NEW-O7RAR81X', 'ZRNTR'),
('10', 'MML3HN48', 'NEW-B02PFB63', 'REVISED'),
('11', '9HBQZ88V', 'NEW-76HSPUAL', 'REVISED'),
('12', 'YI5AT6G4', 'NEW-X8KAWD7Z', 'XYZ'),
('13', 'Z8H2B5KY', '3RINJV0K', 'REVISED');
Query #1
SELECT
`id`, `colA`, `colB`, `revFlag`
FROM
table1 t1
WHERE
(`colA` , IFNULL(`revFlag`,0)) IN
(SELECT
`colA`, `revFlag`
FROM
table1
WHERE
`revFlag` = 'REVISED' UNION SELECT
`colA`, IFNULL(MAX(`revFlag`),0)
FROM
table1
WHERE
`colA` NOT IN (SELECT
`colA`
FROM
table1
WHERE
`revFlag` = 'REVISED')
GROUP BY `colA`)
ORDER BY id;
id
colA
colB
revFlag
2
4F2JG71O
OLD-E71BE63L
4
5H0MWVSB
OLD-V70XLGHT
5
JW73ZX0J
OLD-KME1GXQF
6
XZV0EY0G
OLD-N06BURDF
9
XSR0KA3V
NEW-O7RAR81X
REVISED
10
MML3HN48
NEW-B02PFB63
REVISED
11
9HBQZ88V
NEW-76HSPUAL
REVISED
12
YI5AT6G4
NEW-X8KAWD7Z
XYZ
13
Z8H2B5KY
3RINJV0K
REVISED
View on DB Fiddle