mysql find missing items - mysql

Question

i have a table with the following structure
mysql> describe stock_prices;
+---------------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| code | varchar(16) | YES | MUL | NULL | |
| pricelist | varchar(10) | YES | MUL | NULL | |
| settlement_discount | tinyint(1) | YES | | NULL | |
| overal_discount | tinyint(1) | YES | | NULL | |
| sale | tinyint(1) | YES | | NULL | |
| price_blob | longtext | YES | | NULL | |
+---------------------+-------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)
when i run this query
mysql> SELECT pricelist, count(pricelist) as dup from stock_prices group by pricelist having dup>1 order by dup;
+-----------+------+
| pricelist | dup |
+-----------+------+
| GMBH | 1843 |
| DISTCART | 2241 |
| DISTSTD | 2241 |
| CART | 2242 |
| USSD | 2242 |
| SPCA | 2242 |
| SPCB | 2242 |
| SPCC | 2242 |
| EUCN | 2242 |
| STD | 2242 |
| EUSD | 2242 |
| USCN | 2242 |
+-----------+------+
12 rows in set (0.03 sec)
all the pricelist items should have the same values, but GMBH has 399 less and DISTCART and DISTSTD have 1 less.
basically, i have code that does not have a pricelist entry.
when i run:
mysql> SELECT code, count(code) as dup from stock_prices group by code having dup>1 order by dup;
+-------------+-----+
| code | dup |
+-------------+-----+
| XN44-CH2 | 9 |
| XN23-MGY1 | 11 |
| XN24-CH2 | 11 |
| XN25-VWH1 | 11 |
| XN36-BL2 | 11 |
| XN36-CH3 | 11 |
| XN37-BL3 | 11 |
| XN38-BC3 | 11 |
| XN38-CE3 | 11 |
....
so in this case XN44-CH2 is missing 3 codes and XN23-MGY1 is missing 1 code
mysql> SELECT COUNT(pricelist) FROM stock_prices WHERE pricelist = 'GMBH';
+------------------+
| COUNT(pricelist) |
+------------------+
| 1843 |
+------------------+
1 row in set (0.00 sec)
what would be the correct way to find out what the missing pricelists for each is?
any advice much appreciated.

Answer 1

Assuming there is a reference table for all the price lists and one for all the codes, you could do something like this in standard SQL:
SELECT
p.pricelist,
c.code
FROM
pricelists AS p
CROSS JOIN
codes AS c
EXCEPT
SELECT
pricelist,
code
FROM
stock_prices
;
That is, get all the combinations of the existing pricelists and codes and subtract those that are present in stock_prices. The result would be the missing pairs.
As MySQL doesn't support EXCEPT, you could implement the same logic with a LEFT JOIN:
SELECT
p.pricelist,
c.code
FROM
pricelists AS p
CROSS JOIN
codes AS c
LEFT JOIN
stock_prices AS s ON p.pricelist = s.pricelist
AND c.code = s.code
WHERE s.id IS NULL
;
If you do not have those reference tables, you could replace them with derived tables in this way:
pricelists ==> (SELECT DISTINCT pricelist FROM stock_prices)
codes ==> (SELECT DISTINCT code FROM stock_prices)
And the query would then look like this:
SELECT
p.pricelist,
c.code
FROM
(SELECT DISTINCT pricelist FROM stock_prices) AS p
CROSS JOIN
(SELECT DISTINCT code FROM stock_prices) AS c
LEFT JOIN
stock_prices AS s ON p.pricelist = s.pricelist
AND c.code = s.code
WHERE s.id IS NULL
;