[snip] And the query:

UPDATE table1 INNER JOIN table2 ON table2.ID_table1=table1.ID SET table2.value=table2.value-IF(table1.condition=7,1,0), table1.condition=8 WHERE table1.ID IN (1,2)

After that the value's in table2 are still 5 and 2. But I would expect the 5 to be a 4. [/snip]

It was concerning the warning I sent about InnoDB and the order of precedence.....the query to solve the problem is here....

update table2, table1 SET table2.value=table2.value-IF(table1.condition=7,1,0), table1.condition=8 WHERE table1.ID = table2.ID_table1

Note that you put table1 first in your query above, so table 1 will get updated first. Since that is the case the conditions for updating table2 are never met.