Aktualizujte tabulku pomocí count() z jiné tabulky

Můžete k tomu použít dotaz takto

UPDATE table_a a
SET a.alcohol_spirits = a.alcohol_spirits + 
(SELECT
     count(table_b.itemId)
 FROM table_b
 WHERE headAlias = 'alcohol-spirits' 
 AND country IN('US,SE')
 AND FIND_IN_SET(a.country, table_b.headdestinations)
)