Hierarchical-data using database MySql version 8.0.17

Question

In the table t_contents stored an a database MySql version 8.0.17 I have these rows

+-------------------------+-------+-------+-----+
| Contents                | sID_c | sID_p | sID |
+-------------------------+-------+-------+-----+
| Content 1               |     1 | NULL  |   1 |
| - Gaio Giulio Cesare    |     1 | NULL  |   2 |
| Veni, vidi, vici.       |     1 | NULL  |   3 |
| Carpe diem.             |     1 | NULL  |   4 |
| Ubi maior minor cessat. |     1 | NULL  |   5 |
| - Quinto Orazio Flacco  |     1 | NULL  |   6 |
| Condicio sine qua non.  |     1 | NULL  |   7 |
| Carthago delenda est.   |     1 | NULL  |   8 |
| Content 2               |     2 | NULL  |   9 |
| - Marco Porcio Catone   |     2 | NULL  |  10 |
| Inter sidera versor.    |     2 | NULL  |  11 |
| Content 3               |     3 | NULL  |  12 |
| - Marco Tullio Cicero   |     3 | NULL  |  13 |
| Vivere est cogitare     |     3 | NULL  |  14 |
+-------------------------+-------+-------+-----+

In the column Contents of the table t_contents:

1. The Content 1 it's a Section
2. The - Gaio Giulio Cesare it's a Chapter
3. The Veni, vidi, vici, Carpe diem. and Ubi maior minor cessat. are the paragraph of Chapter
4. etc...

I don’t know the number of Section, Chapter and the paragraph of Chapter … are variables…

I need count these rows and group these rows for sID_c field, to this return

mysql> SELECT
    Contents,
    COUNT(*) q 
FROM
    `t_contents` 
GROUP BY
    sID_c;
+-----------+----+
| Contents  | q  |
+-----------+----+
| Content 1 |  8 |
| Content 2 |  3 |
| Content 3 |  3 |
+-----------+----+
3 rows in set (0.02 sec)

And using the q value, min and max, for return this scheme

+-------------------------+-------+-------+-----+
| Contents                | sID_c | sID_p | sID |
+-------------------------+-------+-------+-----+
| Content 1               |     1 | 1.1   |   1 |
| - Gaio Giulio Cesare    |     1 | 1.2   |   2 |
| Veni, vidi, vici.       |     1 | 1.3   |   3 |
| Carpe diem.             |     1 | 1.4   |   4 |
| Ubi maior minor cessat. |     1 | 1.5   |   5 |
| - Quinto Orazio Flacco  |     1 | 1.6   |   6 |
| Condicio sine qua non.  |     1 | 1.7   |   7 |
| Carthago delenda est.   |     1 | 1.8   |   8 |
| Content 2               |     2 | 2.1   |   9 |
| - Marco Porcio Catone   |     2 | 2.2   |  10 |
| Inter sidera versor.    |     2 | 2.3   |  11 |
| Content 3               |     3 | 3.1   |  12 |
| - Marco Tullio Cicero   |     3 | 3.2   |  13 |
| Vivere est cogitare     |     3 | 3.3   |  14 |
+-------------------------+-------+-------+-----+

Any help would greatly appreciate... Thank you.

-- ----------------------------
-- Table structure for t_contents
-- ----------------------------
DROP TABLE IF EXISTS `t_contents`;
CREATE TABLE `t_contents`  (
  `Contents` varchar(255) DEFAULT NULL,
  `sID_c` int(11) NULL DEFAULT NULL,
  `sID_p` varchar(255) DEFAULT NULL,
  `sID` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`sID`) USING BTREE
) ENGINE = InnoDB;

-- ----------------------------
-- Records of t_contents
-- ----------------------------
INSERT INTO `t_contents` VALUES ('Content 1', 1, NULL, 1);
INSERT INTO `t_contents` VALUES ('- Gaio Giulio Cesare', 1, NULL, 2);
INSERT INTO `t_contents` VALUES ('Veni, vidi, vici.', 1, NULL, 3);
INSERT INTO `t_contents` VALUES ('Carpe diem.', 1, NULL, 4);
INSERT INTO `t_contents` VALUES ('Ubi maior minor cessat.', 1, NULL, 5);
INSERT INTO `t_contents` VALUES ('- Quinto Orazio Flacco', 1, NULL, 6);
INSERT INTO `t_contents` VALUES ('Condicio sine qua non.', 1, NULL, 7);
INSERT INTO `t_contents` VALUES ('Carthago delenda est.', 1, NULL, 8);
INSERT INTO `t_contents` VALUES ('Content 2', 2, NULL, 9);
INSERT INTO `t_contents` VALUES ('- Marco Porcio Catone', 2, NULL, 10);
INSERT INTO `t_contents` VALUES ('Inter sidera versor.', 2, NULL, 11);
INSERT INTO `t_contents` VALUES ('Content 3', 3, NULL, 12);
INSERT INTO `t_contents` VALUES ('- Marco Tullio Cicero', 3, NULL, 13);
INSERT INTO `t_contents` VALUES ('Vivere est cogitare', 3, NULL, 14);

Answer 1

You need to concatenate sID_c with a number returned by ROW_NUMBER() window function:

SELECT Contents, 
       sID_c, 
       CONCAT(sID_c, '.', ROW_NUMBER() OVER (PARTITION BY sID_c ORDER BY sID)) sID_p,
       sID
FROM t_contents

Or if you want to update the table:

WITH cte AS (
  SELECT CONCAT(sID_c, '.', ROW_NUMBER() OVER (PARTITION BY sID_c ORDER BY sID)) sID_p,
         sID
  FROM t_contents
)
UPDATE t_contents t
INNER JOIN cte c ON c.sID = t.sID
SET t.sID_p = c.sID_p

See the demo.