Question

So I have this table where I only want to look at AB.

ID     CODE       COUNT   
102    AB         9
101    AB         8
100    AC         23    //not important!!!!
99     AB         7
98     AB         6
97     AB         5
96     AB         0

I want this table to look like this

ID    NEWID     CODE       COUNT   
102   102       AB         9
101   101       AB         8
99    100       AB         7
98    99        AB         6
97    98        AB         5
96    97        AB         0

How do I get a new ID which counts consecutively where the code is AB?

This is then used for a SELECT query, the initial table should stay intact, so this is not UPDATING the table but just making a fictive NEWID.

Answer 1

You can use a user variable to create a counter to accomplish this (in just one query!):

SELECT t.ID, @NEWID := COALESCE(@NEWID - 1, t.ID) AS NEWID, t.CODE, t.COUNT
FROM
    (SELECT ID, CODE, COUNT FROM some_table WHERE CODE = 'AB' ORDER BY ID DESC) t,
    (SELECT @NEWID := NULL) _uv;

mysql> SELECT t.ID, @NEWID := COALESCE(@NEWID - 1, t.ID) AS NEWID, t.CODE, t.COUNT
    -> FROM
    ->     (SELECT ID, CODE, COUNT FROM some_table WHERE CODE = 'AB' ORDER BY I
D DESC) t,                                                                        
    ->     (SELECT @NEWID := NULL) _uv;
+------+-------+------+-------+
| ID   | NEWID | CODE | COUNT |
+------+-------+------+-------+
|  102 |   102 | AB   |     9 |
|  101 |   101 | AB   |     8 |
|   99 |   100 | AB   |     7 |
|   98 |    99 | AB   |     6 |
|   97 |    98 | AB   |     5 |
|   96 |    97 | AB   |     0 |
+------+-------+------+-------+
6 rows in set (0.03 sec)

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Edit: Here’s an SQL Fiddle for it. (What a cool tool. I had no idea this existed!)