Count rows that have the same value in mysql and then show item number

Question

I have the following data and I was hoping I can group them.

|       Label             |     Category        |
|   PC Equipment          |     Materials       |
|   PC Equipment          |     Materials       |
|   PC Equipment - Install|     Installation    |
|   Table Setup           |     Materials       |
|   Table Setup           |     Materials       |
|   Table Setup - Install |     Installation    |

I wanted to group the following to this output:

| Item #|       Label             |     Category        |
|       |   PC Equipment          |     Materials       |
|       |   PC Equipment          |     Materials       |
|   1   |   PC Equipment - Install|     Installation    |
|       |   Table Setup           |     Materials       |
|       |   Table Setup           |     Materials       |
|   2   |   Table Setup - Install |     Installation    |

Would that be possible? So far this is what I tried

SELECT
    @row_number := CASE WHEN Label LIKE "%Install%" THEN @row_number + 1 
                        ELSE "" 
                   END AS row_number,
    Label       
FROM table1 t,
    (SELECT @rownum := 0) r
WHERE deleted = 0

The output i got was

| Item #|       Label             |     Category        |
|       |   PC Equipment          |     Materials       |
|       |   PC Equipment          |     Materials       |
|   1   |   PC Equipment - Install|     Installation    |
|       |   Table Setup           |     Materials       |
|       |   Table Setup           |     Materials       |
|   1   |   Table Setup - Install |     Installation    |

the second number did not increment.

Answer 1

This is MySQL. You just need to do the variable arithmetic correctly:

SELECT (CASE WHEN Label LIKE '%Install%'
             THEN cast(@icnt := @icnt + 1 as char(10))
             ELSE ''
        END) AS row_number,
       Label       
FROM table1 t CROSS JOIN
     (SELECT @icnt := 0) params
WHERE deleted = 0;

The reason your method doesn't work is because you are re-setting the counter variable on each row. So, it goes from 1 to "" , and the empty string is treated as 0 -- so the next installation, it is incremented to 1. And so on.

Answer 2

Try this:

SELECT IF(Label LIKE "%Install%", rn, '') AS 'Item #',
       Label, Category
FROM (
  SELECT @row_number := CASE 
                           WHEN Label LIKE "%Install%" THEN @row_number + 1
                           ELSE @row_number
                        END AS rn,
         Label, Category
  FROM table1 AS t
  (SELECT @row_number := 0) AS r
  WHERE deleted = 0
  ORDER BY Label) AS t