Mysql update table from another table with condition In mysql i have 2 table.
First

wp_postmeta_import

Second

wp_postmeta_temp

These tables have these columns:

meta_id
post_id
meta_key
meta_value

I need to update only my column meta_value of wp_postmeta_temp when post_id is egual to post id of wp_postmeta_import and the value of meta_key is _variation_description because in table are other post_id with other value
i try some code an this is the only that work a little bit but it is change the row that i need and in the other meta_key it gives me NULL.
UPDATE wp_postmeta_temp  
SET meta_value = (
                    SELECT 
                      meta_value 
                    FROM 
                      wp_postmeta_import 
                    WHERE 
                      wp_postmeta_import.post_id = wp_postmeta_temp.post_id 
                    AND 
                      wp_postmeta_temp.meta_key = '_variation_description' 
                 );

The table have rows, for any post_id for exemple:

meta_id: variable (82649,82650..)
post_id: 5065
meta_key: _variation_description or _regular_price or total_sales ecc..
meta_value: variable (15, 0, 200 ...)

i hope that i'm clear
anyone can help me, please?
you should join the tables, so  that all rows are joint together.
Before you start this use a select with the inner join to see if it fits.
UPDATE wp_postmeta_temp wpmt 
INNER JOIN wp_postmeta_import wpi ON wpi.post_id=wpmt.post_id AND wpmt.meta_key = '_variation_description'
   SET wpmt.meta_value= wpi.meta_value