My SQL query within a query
I have 2 tables that I am trying to combine in a specific way Table 1: ‘part_defs’ Table 2 Items_part_values
in value_defs:
开发者_JAVA技巧ID | Name
-------------
1 | color
2 | size
3 | weight
in Items_part_values
ItemID | valueID | Value
-------------------------
10 | 1 | red
11 | 1 | blue
What I need is a query where for a given item all the rows from value_defs appear and if they have a value in Items_part_values the value.
So for Item 11 I want
ID | Name | Value
--------------------
1 | color | red
2 | size | NULL
3 | weight | NULL
I’m new to MySQL, in access I would have created a subquery with the ItemID as a parameter and then done a Left Join with value_defs on the result.
Is there a way of doing something similar in MySQL?
Thanks
Use:
SELECT p.id,
p.name,
ipv.value
FROM PART_DEFS p
LEFT JOIN ITEMS_PART_VALUES ipv ON ipv.valueid = p.id
AND ipv.itemid = ?
Replace the "?" with the itemid you want to search for.
This means all the PARTS_DEF
rows will be returned, and if the ITEMS_PART_VALUES.valueid
matches the PART_DEFS.id
value, then the ITEMS_PART_VALUES.value
value will be displayed for the item you are looking for. If there's no match, the value column will be NULL for that record.
There's a difference in OUTER JOINs, when specifying criteria in the JOIN vs the WHERE clause. In the JOIN, the criteria is applied before the JOIN occurs while in the WHERE
clause the criteria is applied after the JOIN.
Use a left join:
SELECT * FROM Table1 LEFT JOIN Table2 USING (ID);
Edit:
SELECT * FROM part_defs LEFT JOIN Items_part_values ON part_defs.ID = Items_part_values.valueID;
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