I have a mysql query which is to return the only 1 record that need to cross multiple table. However, the mysql query is slow when executing.

Query:

```
SELECT *, 
(SELECT TreeName FROM sys_tree WHERE TreeId = Mktg_Unit_Booking.ProjectLevelId) AS PhaseName, 
(CASE WHEN ProductType = 'U' THEN (SELECT UnitNo FROM prop_unit pu WHERE pu.UnitId = mktg_unit_booking.UnitId) 
ELSE (SELECT BayNo FROM prop_car_park pcp WHERE pcp.CarParkId = UnitId) END) AS UnitNo, 
(SELECT CustomerName FROM mktg_customer mc WHERE mc.CustomerId = mktg_unit_booking.CustomerId) AS CustomerName 
FROM Mktg_Unit_Booking 
WHERE IsDeleted <> '1' AND IsApproved = '1' 
AND UnitId = 1110 AND ProductType = 'U' 
ORDER BY UnitNo

```

I have run EXPLAIN in the query and I got this:

[![EXPLAIN TABLE](https://i.stack.imgur.com/fgwWv.jpg)](https://i.stack.imgur.com/fgwWv.jpg)

Any other suggestion on how to improve the speed of the query?
Thank you!