How to update in MySql columns - mysql

Question

There are 5 columns X and A, B, C, D in table t. Columns A, B, C, D are varchar. and column X has to show us how many of the next row repeating characters. I need help to update column X.
Example :
|ID | X | A | B | C | D |
=========================
| 4 | 1 | 7 | J | 7 | Q |
| 3 | 2 | K | Q | 8 | 8 |
| 2 | 3 | 7 | 8 | 9 | J | next row X=3
| 1 | 0 | 7 | J | 8 | K | 0 default
ID-1 is the first and X is zero by default and from there begin calculations ID-2 and X=3 because we have ID-1 "7" "J" and "8" and the next row ID-2 have the combination "7 8 9 J" in ID-1 there "7 J 8 -" and X should be 3. Values ​​of X can be between 0 and 4. ID-3, X=2 "- - 8 8" because in ID-2 have the combination "7 8 9 J" and i have 8 - twice in "K Q 8 8".

Answer 1

Added : 08/06
http://sqlfiddle.com/#!2/4586e/1
CREATE TABLE tmp
(
id int,
alnum CHAR(1),
cnt int,
PRIMARY KEY (id, alnum)
);
INSERT INTO tmp (id, alnum, cnt) SELECT id, A, 1 FROM tab ON DUPLICATE KEY UPDATE cnt = cnt + 1;
INSERT INTO tmp (id, alnum, cnt) SELECT id, B, 1 FROM tab ON DUPLICATE KEY UPDATE cnt = cnt + 1;
INSERT INTO tmp (id, alnum, cnt) SELECT id, C, 1 FROM tab ON DUPLICATE KEY UPDATE cnt = cnt + 1;
INSERT INTO tmp (id, alnum, cnt) SELECT id, D, 1 FROM tab ON DUPLICATE KEY UPDATE cnt = cnt + 1;
UPDATE tab INNER JOIN (
SELECT t1.id AS id, SUM(t2.cnt) AS sum
FROM tmp t1 INNER JOIN tmp t2 ON t1.id + 1 = t2.id
AND t1.alnum = t2.alnum
GROUP BY t1.id
) tmp3 ON tab.id = tmp3.id + 1
SET tab.X = tmp3.sum;
SELECT * FROM tab WHERE X > 4;
Original answer : 08/05
How about using tmp table which stores for each A, B, C, D columns into single rows. This makes us easy to calculate X value.
Below code assumes id is sequencial value. If not, please let me know there is another query for it.
CREATE TABLE tab
(
id INT,
X INT,
A CHAR(1),
B CHAR(1),
C CHAR(1),
D CHAR(1)
);
INSERT INTO tab VALUES (1, 0, '7', 'J', '8', 'K');
INSERT INTO tab VALUES (2, 0, '7', '8', '9', 'J');
INSERT INTO tab VALUES (3, 0, 'K', 'Q', '8', '8');
INSERT INTO tab VALUES (4, 0, '7', 'J', '7', 'Q');
CREATE TABLE tmp
(
id INT,
alnum CHAR(1)
);
INSERT INTO tmp SELECT id, A FROM tab;
INSERT INTO tmp SELECT id, B FROM tab;
INSERT INTO tmp SELECT id, C FROM tab;
INSERT INTO tmp SELECT id, D FROM tab;
UPDATE tab INNER JOIN (
SELECT t1.id AS id, COUNT(*) AS cnt
FROM tmp t1 INNER JOIN tmp t2 ON t1.id + 1 = t2.id
AND t1.alnum = t2.alnum
GROUP BY t1.id
) tmp3 ON tab.id = tmp3.id + 1
SET tab.X = tmp3.cnt;
mysql> SELECT * FROM tab ORDER BY id DESC;
+------+------+------+------+------+------+
| id | X | A | B | C | D |
+------+------+------+------+------+------+
| 4 | 1 | 7 | J | 7 | Q |
| 3 | 2 | K | Q | 8 | 8 |
| 2 | 3 | 7 | 8 | 9 | J |
| 1 | 0 | 7 | J | 8 | K |
+------+------+------+------+------+------+
4 rows in set (0.00 sec)

Answer 2

The X values in your example are from the "next" row, not the previous. Assuming you have an auto-incrementing id, you can calculate this information by looking at the next row. You can generate a query to do the calculation:
select ((case when t1.A in (tnext.A, tnext.B, tnext.C, tnext.D) then 1 else 0 end) +
(case when t1.B in (tnext.A, tnext.B, tnext.C, tnext.D) then 1 else 0 end) +
(case when t1.C in (tnext.A, tnext.B, tnext.C, tnext.D) then 1 else 0 end) +
(case when t1.D in (tnext.A, tnext.B, tnext.C, tnext.D) then 1 else 0 end)
) as X, t1.*
from (select t.*, (select max(id) from table t2 where t2.id > t.id) as nextid
from table t
) t1 left outer join
t tnext
on tnext.id = t1.nextid;
Depending on the database you are using, this code can be simplified and expressed differently. Also, the specific update syntax might depend on the database.