CODEWITHSUNDEEP
phpmysqlsql
mrmryb
mrmryb

Reputation: 1509

Compare column from two rows and if different change values of another column

I have a table with an auto increment key id, item_no can be either one or two rows in a row (so they always have consecutive ids) that share the same ref but have different right/left (but technically item_no can be repeated multiple times throughout the table but that's not an issue), and description will sometimes be the same on the consecutive rows but sometimes different:

id | item_no | description | right\left | ref
1  | 1       | a1          | right      | aaa
2  | 1       | a1          | left       | aaa
3  | 2       | b1          | right      | bbb
4  | 3       | c1          | right      | ccc
5  | 3       | c2          | left       | ccc
6  | 4       | d1          | right      | ddd
7  | 4       | d1          | left       | ddd

My issue is that I need item_no to append a -r or -l on to its value if the description of its 'matching' row is different.

So the result I am looking for is:

id | item_no | description | right\left | ref
1  | 1       | a1          | right      | aaa
2  | 1       | a1          | left       | aaa
3  | 2       | b1          | right      | bbb
4  | 3-r     | c1          | right      | ccc
5  | 3-l     | c2          | left       | ccc
6  | 4       | d1          | right      | ddd
7  | 4       | d1          | left       | ddd

I am exporting the table to a csv but am not using much php, just a mysql statement and then looping out the results, is this possible within the mysql statement or will I have to rely on a php loop?

Upvotes: 2

Views: 921

Answers (4)

RTB
RTB

Reputation: 5833

I would rely on a PHP loop if you're using mysql, if you were using Oracle or SQL server then you could program a stored procedure.

You script should look something like this:

$dbh = new PDO('mysql:host='.DATABASE_HOST.';dbname='.DATABASE_NAME, DATABASE_USER, DATABASE_PASSWORD);
$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

$data = $dbh->query("SELECT * FROM ExampleTable");
$dbh->beginTransaction();

foreach($data as $row)
{
    $append = $row["right\left"] == "left" ? $row["item_no"]."-l" : $row["item_no"]."-r";
    $stmnt = $dbh->prepare("UPDATE ExampleTable SET item_no = :item WHERE id = :id");
    $stmnt->execute(array(":item" => $append,":id" => $row["id"]));
}

// Do some exception handling if something goes wrong you can allways do a rollback
// With PDO $dbh->rollBack();
$dbh->commit();
$dbh = null;

Upvotes: 1

fthiella
fthiella

Reputation: 49089

I would use this:

update
  items inner join
  (select item_no from items
   group by item_no
   having count(distinct description)>1) dup
  on items.item_no=dup.item_no
set
  items.item_no=concat(items.item_no, '-', substr(rightleft, 1,1))

If rows are always consecutive, you could also use this:

update
  items i1 inner join items i2
  on (i1.id=i2.id+1 or i1.id=i2.id-1) 
     and (i1.item_no=i2.item_no)
     and (i1.description<>i2.description)
set i1.item_no=concat(i1.item_no, '-', substr(i1.rightleft, 1,1))

EDIT: if rows are always consecutive, and you just need a select and not an update, you could use this:

select
  i1.id,
  case when i1.description=i2.description or i2.id is null then i1.item_no else
            concat(i1.item_no, '-', substr(i1.rightleft, 1,1)) end,
  i1.description, i1.rightleft, i1.ref
from
  items i1 left join items i2
  on (i1.id=i2.id+1 or i1.id=i2.id-1) and (i1.item_no=i2.item_no)
order by i1.id

Upvotes: 2

Mahmoud Gamal
Mahmoud Gamal

Reputation: 79979

Try this:

SELECT 
  id, 
  CASE RightLeft
    WHEN  'right' THEN CONCAT(item_no, '-r' )
    WHEN  'left'  THEN CONCAT(item_no, '-l' )
  END AS item_no,
  DESCRIPTION,
  Rightleft,
  ref
FROM Items
WHERE item_no IN
(
  SELECT i1.item_no
  FROM items i1
  GROUP BY i1.item_no
  HAVING(COUNT(DISTINCT description)) > 1);

SQL Fiddle Demo

This will give you:

| ID | ITEM_NO | DESCRIPTION | RIGHTLEFT | REF |
------------------------------------------------
|  4 |     3-r |          c1 |     right | ccc |
|  5 |     3-l |          c2 |      left | ccc |

Upvotes: 1

Mehdi Bugnard
Mehdi Bugnard

Reputation: 3979

Something like this

UPDATE [dbo].[maTable] SET [item_no] = [item_no]+'r' WHERE not distinct [description] from [dbo].[maTable]

Should add an 'r' in the registration line where [description] is not identical (coded for SQL Server)

Upvotes: 0

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