Converting strange SQL Server JOIN syntax to MySQL syntax - sql

Question

I have a SQL Server query that I am attempting to port to MySQL, but the JOIN syntax is something that I have never seen used before. The query is from a view designed to measure procedure code usage. What the heck is going on with the JOIN syntax just past T.PatID = P.ID, and the third LEFT OUTER JOIN, and what equivalent syntax can we use in MySQL? It does not like this JOIN syntax at all (disregard the ISNULL and CONVERT SQL Server specific syntax)
SELECT
T.Code
, P.LastName
, P.FirstName
, T.TranDate
, CD.DaysUnits
, T.TranAmt
, TD.FullName AS Provider
, ISNULL(TD.ID, ISNULL(AD.ID, PD.ID)) AS DoctorID
FROM
dbo.Doctors AS PD
INNER JOIN
dbo.Transactions AS T
INNER JOIN
dbo.Patients AS P
ON
T.PatID = P.ID
ON
PD.ID = P.DoctorID
LEFT OUTER JOIN
dbo.Doctors AS TD
ON
T.DoctorID = TD.ID
LEFT OUTER JOIN
dbo.Doctors AS AD
LEFT OUTER JOIN
dbo.Appointments
ON
AD.ID = dbo.Appointments.DoctorID
AND CONVERT(varchar(20), dbo.Appointments.ScheduleDateTime, 8) <> '00:00:00'
ON
T.ApptID = dbo.Appointments.ID
LEFT OUTER JOIN
dbo.ChargeDetails AS CD
ON
T.ID = CD.ChargeTranID
WHERE
(
T.Code IS NOT NULL
)
The SHOW CREATE TABLE are as follows
CREATE TABLE Doctors
(
ID int(10) NOT NULL PRIMARY KEY
, FullName varchar(50) DEFAULT NULL
)
CREATE TABLE Patients
(
LName varchar(50) DEFAULT NULL
, FName varchar(50) DEFAULT NULL
, ID int(10) NOT NULL PRIMARY KEY
)
CREATE TABLE Transactions
(
TranType varchar(2) DEFAULT NULL
, Code varchar(100) DEFAULT NULL
, TranSubType varchar(2) DEFAULT NULL
, Description varchar(2000) DEFAULT NULL
, TranDate datetime
, PatID int(10) DEFAULT NULL
, ID int(10) NOT NULL PRIMARY KEY
, TranAmt decimal(19,4) DEFAULT NULL
, ApptID int(10) DEFAULT NULL
, DoctorID int(10) DEFAULT NULL
)
CREATE TABLE ChargeDetails
(
DaysUnits varchar(50) DEFAULT NULL
-- DaysUnits is just an int ranging from 1 to 2
, ChargeTranID int(10) NOT NULL PRIMARY KEY
)
CREATE TABLE Appointments
(
DoctorID int(10) DEFAULT NULL
, PatientID int(10) DEFAULT NULL
, ScheduleDateTime datetime DEFAULT NULL
, ID int(10) NOT NULL PRIMARY KEY
)
Thank you in advance for your help.

Answer 1

Here is a similar (and simplified) query using the same structure as the first query. The second query moves the joins around to make things easier to read.
set nocount on;
use tempdb;
go
declare #doc table (id int not null);
declare #tran table (id int not null, patid int not null);
declare #patients table (id int not null, docid int not null);
insert #doc (id) values (1);
insert #patients (id, docid) values (25, 1);
insert #tran (id, patid) values (100, 25)
select *
from #doc as pd
inner join #tran as t
inner join #patients as p
on t.patid = p.id
on pd.id = p.docid;
select *
from #tran as t
inner join #patients as p
on t.patid = p.id
inner join #doc as pd
on pd.id = p.docid;
Other things look strange. I don't see a need to join to appointments but I'm not going to spend a lot of time to figure out the logic and the schema. The convert usage seems like a bad way to check for null - unless there is a special "flag" datetime value that is used as the equivalent to null. Again, you need to understand the query, the goal of the query, the schema on which it is based, and how the tables are populated. Quite frankly, this code raises concerns about the quality of the entire system.
.