MYSQL - table display options (do not print duplicates) - mysql

Question

I am looking into the options when printing mysql table. It is simple task but I could not find any help so far.
I have a table (tbl_2) and it looks like that:
+------+------+------+------+--------+---------+
| code | PN | Alt | Link | PN_Val | Alt_Val |
+------+------+------+------+--------+---------+
| 1 | A | B | 1 | 4 | 4 |
| 2 | A | B | 1 | 4 | 1 |
| 3 | B | Z | 0 | 3 | 2 |
| 4 | B | Z | 0 | 3 | 1 |
| 5 | B | Z | 0 | 3 | 3 |
| 6 | F | G | 1 | 2 | 2 |
| 7 | F | G | 1 | 2 | 1 |
+------+------+------+------+--------+---------+
What I am trying to show is the following
+------+------+------+------+--------+---------+
| code | PN | Alt | Link | PN_Val | Alt_Val |
+------+------+------+------+--------+---------+
| 1 | A | B | 1 | 4 | 4 |
| 2 | | | | | 1 |
| 3 | B | Z | 0 | 3 | 2 |
| 4 | | | | | 1 |
| 5 | | | | | 3 |
| 6 | F | G | 1 | 2 | 2 |
| 7 | | | | | 1 |
+------+------+------+------+--------+---------+
In the nutshell I try to have anything that is duplicated removed.
Code for mysql:
create table tbl_2 (
code int(10) primary key,
PN varchar(10),
Alt varchar(10),
Link varchar(10),
PN_Val int(10),
Alt_Val int(10));
insert into tbl_2 values
(1, 'A', 'B', '1', 4, 4),
(2, 'A', 'B', '1', 4, 1),
(3, 'B', 'Z', '0', 3, 2),
(4, 'B', 'Z', '0', 3, 1),
(5, 'B', 'Z', '0', 3, 3),
(6, 'F', 'G', '1', 2, 2),
(7, 'F', 'G', '1', 2, 1);

Answer 1

If you want do that in SQL.
You can try to use a subquery in CASE WHEN
Schema (MySQL v5.7)
create table tbl_2 (
code int(10) primary key,
PN varchar(10),
Alt varchar(10),
Link varchar(10),
PN_Val int(10),
Alt_Val int(10));
insert into tbl_2 values (1, 'A', 'B', '1', 4, 4);
insert into tbl_2 values (2, 'A', 'B', '1', 4, 1);
insert into tbl_2 values (3, 'B', 'Z', '0', 3, 2);
insert into tbl_2 values (4, 'B', 'Z', '0', 3, 1);
insert into tbl_2 values (5, 'B', 'Z', '0', 3, 3);
insert into tbl_2 values (6, 'F', 'G', '1', 2, 2);
insert into tbl_2 values (7, 'F', 'G', '1', 2, 1);
Query #1
SELECT code,
(CASE WHEN code = (select min(code) from tbl_2 tt WHERE tt.PN = t1.PN and tt.Alt = t1.Alt GROUP BY PN,Alt) THEN PN END) PN,
(CASE WHEN code = (select min(code) from tbl_2 tt WHERE tt.PN = t1.PN and tt.Alt = t1.Alt GROUP BY PN,Alt) THEN Alt END) Alt,
(CASE WHEN code = (select min(code) from tbl_2 tt WHERE tt.PN = t1.PN and tt.Alt = t1.Alt GROUP BY PN,Alt) THEN Link END) Link,
(CASE WHEN code = (select min(code) from tbl_2 tt WHERE tt.PN = t1.PN and tt.Alt = t1.Alt GROUP BY PN,Alt) THEN PN_Val END) PN_Val,
Alt_Val
FROM tbl_2 t1;
| code | Alt_Val | PN | Alt | Link | PN_Val |
| ---- | ------- | --- | --- | ---- | ------ |
| 1 | 4 | A | B | 1 | 4 |
| 2 | 1 | | | | |
| 3 | 2 | B | Z | 0 | 3 |
| 4 | 1 | | | | |
| 5 | 3 | | | | |
| 6 | 2 | F | G | 1 | 2 |
| 7 | 1 | | | | |
View on DB Fiddle

Answer 2

As the above comments suggest, this is a requirement which might be best or typically handled in your presentation layer, e.g. something like PHP. But, with MySQL 8+ this is fairly easy to handle with a single query:
WITH cte AS (
SELECT *,
ROW_NUMBER() OVER (PARTITION BY PN ORDER BY code) rn
FROM yourTable
)
SELECT
code,
CASE WHEN rn = 1 THEN PN ELSE '' END AS PN,
CASE WHEN rn = 1 THEN Alt ELSE '' END AS Alt,
CASE WHEN rn = 1 THEN Link ELSE '' END AS Link,
-- show NULL for missing values in the next two integer columns
CASE WHEN rn = 1 THEN PN_Val END AS PN_Val,
CASE WHEN rn = 1 THEN Alt_Val END AS Alt_Val
FROM cte
ORDER BY code;
Demo