来自2个不同表的MySQL SELECT，其中2个表具有WHERE子句，并且1个结果为NULL

Question

I am trying to get the ordered qty in the cart_items table and the shipped qty in the shipping_table . Problem is, some skus haven't shipped yet and I can either A) only pull the items shipped or B) not have the correct total shipped qty.

SAMPLE DATA

`shipping_table`    
id  |  invoice  | sku   | qty  | order_id
99  |   104     | 15628 |  1   |  9313
98  |   104     | 34929 |  2   |  9313
97  |   103     | 34929 |  1   |  9313
96  |   102     | 15628 |  87  |  9999
95  |   101     | 34929 |  32  |  9999
94  |   100     | 35870 |  6   |  9999


`cart_items`    
id     |  cart_id | sku   | qty
64903  |  4935153 | 15628 |  1  
65108  |  4935153 | 34929 |  4  
65109  |  4935153 | 35870 |  4  

In this result we should see that sku 35870 hasn't shipped any items, 15628 has shipped, and sku 34929 only has shipped 3 items.

EXPECTED RESULT

sku   | total_qty | total_shipped_qty
15628 |      1    |          1
34929 |      4    |          3
35870 |      4    |          NULL   

WRONG RESULT A

This one is close but since I am querying on an order_id which is only in one table it doesn't pull the total_qty for the sku 35870 because it is not in shipping_table yet (it hasn't shipped at all).

SELECT 
    CT.sku, 
    MT.`qty` as total_qty, 
    SUM(CT.`qty`) as total_shipped_qty 
FROM `shipping_table` CT 
        LEFT JOIN 
     `cart_items` MT ON MT.sku = CT.sku 
WHERE MT.`cart_id` = '4935153' AND CT.`order_id` = '9313'
GROUP BY MT.sku

sku   | total_qty | total_shipped_qty
15628 |      1    |          1
34929 |      4    |          3

WRONG RESULT B

Here is something close but it is the incorrect total_shipped_qty values because it is looking at the Total in the whole shipping_table . This result looks like it sums up the WHOLE qtys for the shipping_table .

SELECT 
    CT.sku, 
    MT.`qty` as total_qty, 
    SUM(CT.`qty`) as total_shipped_qty 
FROM `shipping_table` CT 
        LEFT JOIN 
     `cart_items` MT ON MT.sku = CT.sku 
WHERE MT.`cart_id` = '4935153'
GROUP BY MT.sku

sku   | total_qty | total_shipped_qty
15628 |      1    |          88
34929 |      4    |          35
35870 |      4    |          6

Answer 1

Use Scalar Subquery

DEMO

SELECT 
     CT.sku, 
     qty as total_qty, 
    (select SUM(qty) from shipping_table MT where CT.sku=MT.sku group by MT.sku) 
    as total_shipped_qty 
FROM cart_items CT
      WHERE CT.cart_id = '4935153'