The optimization process and recommendations:

1. Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.
2. Use Numeric Column Types For Numeric Values (query line: 25): Referencing a numeric value (e.g. 1234) as a string in a WHERE clause might result in poor performance. Possible impacts of storing numbers as varchars: more space will be used, you won't be able to perform arithmetic operations, the data won't be self-validated, aggregation functions like SUM won't work, the output may sort incorrectly and more. If the column is numeric, remove the quotes from the constant value, to make sure a numeric comparison is done.
3. Use Numeric Column Types For Numeric Values (query line: 26): Referencing a numeric value (e.g. 5678) as a string in a WHERE clause might result in poor performance. Possible impacts of storing numbers as varchars: more space will be used, you won't be able to perform arithmetic operations, the data won't be self-validated, aggregation functions like SUM won't work, the output may sort incorrectly and more. If the column is numeric, remove the quotes from the constant value, to make sure a numeric comparison is done.
4. Use Numeric Column Types For Numeric Values (query line: 15): Referencing a numeric value (e.g. 01) as a string in a WHERE clause might result in poor performance. Possible impacts of storing numbers as varchars: more space will be used, you won't be able to perform arithmetic operations, the data won't be self-validated, aggregation functions like SUM won't work, the output may sort incorrectly and more. If the column is numeric, remove the quotes from the constant value, to make sure a numeric comparison is done.
5. Use Numeric Column Types For Numeric Values (query line: 19): Referencing a numeric value (e.g. 01) as a string in a WHERE clause might result in poor performance. Possible impacts of storing numbers as varchars: more space will be used, you won't be able to perform arithmetic operations, the data won't be self-validated, aggregation functions like SUM won't work, the output may sort incorrectly and more. If the column is numeric, remove the quotes from the constant value, to make sure a numeric comparison is done.

Optimal indexes for this query:

ALTER TABLE `customer` ADD INDEX `customer_idx_id1_id2` (`id1`,`id2`);
ALTER TABLE `order_entry` ADD INDEX `order_entry_idx_order_id1_id2_order` (`order_status`,`id1`,`id2`,`order_type`);
ALTER TABLE `order_history` ADD INDEX `order_history_idx_order_id1_id2_order` (`order_status`,`id1`,`id2`,`order_type`);

The optimized query:

SELECT
        c.id1,
        c.id2,
        (SELECT
            (sum(oe.revenue1) + sum(oe.revenue2) + sum(h.revenue1) + sum(h.revenue2)) * .01 
        FROM
            order_entry oe,
            order_history h 
        WHERE
            c.id1 = oe.id1 
            AND c.id2 = oe.id2 
            AND c.id1 = h.id1 
            AND c.id2 = h.id2 
            AND oe.order_type IN (
                '01', '02', '03', '04'
            ) 
            AND oe.order_status = 'CLOSED' 
            AND h.order_type IN (
                '01', '02', '03', '04'
            ) 
            AND h.order_status = 'CLOSED') AS total_revenue 
    FROM
        customer c 
    WHERE
        c.id1 = '1234' 
        AND c.id2 = '5678'