MySQL UNION vs JOIN使用OR in子句

Question

I have one table TableA with columns [AccountID, Email] . I have another table TableB with [AccountID_1, AccountID_2, email] . I need to match the AccountID in TableA with either of the AccountIDs in TableB . Neither of these approaches seem to be working. The first one seems to be stalling or just taking forever (both tables have several hundred thousand entries). The second has the error "Can't reopen table: TableB".

Attempting JOIN with OR

select count(distinct TableA.id) from TableA
    JOIN TableB ON TableB.AccountID = TableA.AccountID_1 
    OR TableB.AccountID = TableA.AccountID_2
;

Attempting sql UNION

select count(distinct b.id) from (
    select * from TableA
    join TableB on TableB.AccountID = TableA.AccountID_1 
    union
    select * from TableA
    join TableB on TableB.AccountID = TableA.AccountID_2
) as b;

Answer 1

You could try

select count(*) from TableA where
exists ( select 1 from TableB where
AccountID in (AccountID_1,AccountID_2))

Answer 2

For the first one, the column name being selected is wrong. The following seem to work fine.

Attempting JOIN with OR :

select count(distinct `TableA`.AccountID) from `TableA`
    JOIN TableB ON (TableA.AccountID = TableB.AccountID_1 
        OR TableA.AccountID = TableB.AccountID_2);

Attempting SQL UNION

select count(distinct b.AccountID) from (
    select `AccountID` from TableA
    join TableB on TableA.AccountID = TableB.AccountID_1 
    union
    select `AccountID` from TableA
    join TableB on TableA.AccountID = TableB.AccountID_2
) as b;