How to Generate new number each time when value changes - sql

Question

I need to generate a random number based on below three conditions
Generate new PRCnumber when color changes
Generate new PRCnumber when the day changes
Generate new PRCnumber when color remains same but shirt number
changes within the day.
The random number will be used as identifier for the lot of the products generated. Shirt table will have the shirt number and respective color details.
Below is the query I will be using to fetch and it will take shirt number Shirt_num as input
select shirt.facility,
shirt.color,
shirt.lotnum,
colorMgr.untpal,
colorMgr.style,
shirt.product_line
from shirt,
colorMgr,
products
where colorMgr.facility = shirt.facility
and colorMgr.color = shirt.color
and colorMgr.color_id = shirt.color_id
and shirt.product_line = products.product_line
and shirt.shirtnum = #shirtnum;
I want to write conditions something like but not sure how to catch and compare when new color keeps changing.
if day_changes ()
SELECT RAND() as prcnumber
else if shirt_num_changes()
SELECT RAND() as prcnumber
else if color_changes ()
SELECT RAND() as prcnumber
..........
The desired output will be something like this.
shirt_num RandomNum Color Day
1111011 384700412 Black 26 Feb, 2021
1111011 384700132 Black 27 Feb, 2021 (Random numbr when day changes)
1111017 384701792 Black 26 Feb, 2021 (Random numbr when shirt_num changes)
1111011 384700458 Blue 26 Feb, 2021 (Random numbr when color changes)

Answer 1

You can do what you want with window functions, but it would depend on the ordering of the query, and it would not be deterministic (you'd get a different number each query).
I would instead recommend using a checksum of the fields.
mysql> select *, sha1(concat_ws('|', shirtnum, color, day)) from shirts;
+----------+-------+------------+--------------------------------------------+
| shirtnum | color | day | sha1(concat_ws('|', shirtnum, color, day)) |
+----------+-------+------------+--------------------------------------------+
| 111 | black | 2021-02-26 | ad48a0f6b9b197ce11a78a85bca70a487af8f028 |
| 111 | black | 2021-02-26 | ad48a0f6b9b197ce11a78a85bca70a487af8f028 |
| 111 | blue | 2021-02-26 | d863fb4761e0deae3815b6f1ab53c69d5a1a2958 |
| 222 | black | 2021-02-26 | a5dbace4af2bd0510178dcb05065392f2a73d3c0 |
| 222 | black | 2021-02-27 | 1906c453b7bff2b140bb972be8ba29fa80260392 |
| 222 | black | 2021-02-27 | 1906c453b7bff2b140bb972be8ba29fa80260392 |
| 111 | black | 2021-02-27 | c0061ba0d2be5d261c0f7ddcb28ccd8de0ea7c52 |
+----------+-------+------------+--------------------------------------------+
The advantage is this is deterministic and does not depend on the order of the results.
You can implement this as a generated column if your database supports that, or with a view.
mysql> create view shirt_ids as select *, sha1(concat_ws('|', shirtnum, color, day)) as whatever_this_is from shirts;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from shirt_ids;
+----------+-------+------------+------------------------------------------+
| shirtnum | color | day | whatever_this_is |
+----------+-------+------------+------------------------------------------+
| 111 | black | 2021-02-26 | ad48a0f6b9b197ce11a78a85bca70a487af8f028 |
| 111 | black | 2021-02-26 | ad48a0f6b9b197ce11a78a85bca70a487af8f028 |
| 111 | blue | 2021-02-26 | d863fb4761e0deae3815b6f1ab53c69d5a1a2958 |
| 222 | black | 2021-02-26 | a5dbace4af2bd0510178dcb05065392f2a73d3c0 |
| 222 | black | 2021-02-27 | 1906c453b7bff2b140bb972be8ba29fa80260392 |
| 222 | black | 2021-02-27 | 1906c453b7bff2b140bb972be8ba29fa80260392 |
| 111 | black | 2021-02-27 | c0061ba0d2be5d261c0f7ddcb28ccd8de0ea7c52 |
+----------+-------+------------+------------------------------------------+