MySQL用第一张表中的数据填充第二张表

Question

There are two tables in the MySQL db:

Dictionary Table:
**item | description**
--------------------
item1 | Description1
item2 | Description2
........
item1000000 | Description1000000


**Unknown**:
**item | description**
--------------------
item33 | NULL
item1234 | NULL
item8599 | NULL

I need to fill out the description column of Unknown table by the correspondent data of Dictionary table.

How to make it with one query?

So the result would be

item | description
--------------------
item33 | Description33
item1234 | Description1234
item8599 | Description8599

Answer 1

You can use the multiple-table UPDATE syntax to join the tables:

UPDATE Unknown JOIN Dictionary USING (item)
SET    Unknown.description = Dictionary.description

Answer 2

Use an Update with a Join :

update unknown u 
join dictionary d on u.item = d.item
set u.description = d.description