MySQL: join to SELECT statement issue - mysql

Question

I've created the following stored procedure:
CREATE PROCEDURE `sp_DBR_Subbie_Cert_Input`(inPlot_ID varchar(25), inSubbie varchar(25), inCertDate date, inCertDetails varchar(50), inCertGross float ) BEGIN
SELECT inPlot_ID as 'Plot[Unit]', inSubbie as 'Subcontractor[inSub_ID]', inCertDate as 'Date[inC_Date]', inCertDetails as 'Details[inC_Det]', inCertGross as 'Gross[inC_Gross]', a.tblCert_Number as 'Prev. Cert#', a.tblCert_Gross as 'Prev Gross[inC_Prev]'
FROM hilmark.tblcertificates_j a
JOIN
(SELECT max(tblcertificates_j.tblCert_ID) as MaxCertID,
tblcertificates_j.tblCert_XID456 as MaxSubbie, tblcertificates_j.tblCert_XIDJob as MaxPlot
FROM hilmark.tblcertificates_j
GROUP BY tblcertificates_j.tblCert_XIDJob) x
WHERE x.MaxCertID=a.tblCert_ID AND x.MaxPlot=inPlot_ID AND x.MaxSubbie=inSubbie;
END $$
What I am trying to achieve is to allow a user to enter a new invoice for a supplier for a site. The query retrieves the last invoice for that supplier and that site. This works great except when this is the first invoice for that supplier on that site - nothing is returned. What I really need is a left outer join but in my code if I substitute the join with a left join I get a syntax error.
Where am I going wrong here?

Answer 1

I declared a variable called Max_CerT_ID and set it's value to the Cert_ID from the table or to zero if it's a completely new supplier. I then use this variable in case statements.
DROP PROCEDURE IF EXISTS sp_DBR_Subbie_Cert_Input
$$
CREATE PROCEDURE `sp_DBR_Subbie_Cert_Input`(inPlot_ID varchar(25), inSubbie varchar(25), inCertDate date, inCertDetails varchar(50), inCertGross float )
BEGIN
declare Max_Cert_Id int(11);
set Max_Cert_Id=0;
select max(y.tblCert_ID) into Max_Cert_ID from
hilmark.tblcertificates_j y
where y.tblCert_XIDJob=inPlot_ID and y.tblCert_XID456=inSubbie
group by y.tblCert_XIDJob, y.tblCert_XID456 ;
select 'dbr.colstyle',6,'%0.0F';
select 'dbr.colstyle',7,'%0.0F';
select 'dbr.colstyle',8,'%0.0F';
select inPlot_ID as 'Plot[Unit]',
inSubbie as 'Subcontractor[inSub_ID]',
inCertDate as 'Date[inC_Date]',
case
when Max_Cert_Id=0 then 1
else (select a.tblCert_Number from hilmark.tblcertificates_j a where a.tblCert_ID=Max_Cert_ID)+1
end as 'Cert#',
upper(inCertDetails) as 'Details[inC_Det]',
inCertGross as 'Gross[inC_Gross]',
case
when Max_Cert_Id=0 then 0
else (select a.tblCert_Gross from hilmark.tblcertificates_j a where a.tblCert_ID=Max_Cert_ID)
end as 'Prev. Gross',
case
when Max_Cert_Id=0 then inCertGross
else inCertGross-(select a.tblCert_Gross from hilmark.tblcertificates_j a where a.tblCert_ID=Max_Cert_ID)
end as 'Change in WIP';
END
$$

Answer 2

Try writing the query as:
SELECT inPlot_ID as `Plot[Unit]`, inSubbie as `Subcontractor[inSub_ID]`,
inCertDate as `Date[inC_Date]`, inCertDetails as `Details[inC_Det]`,
inCertGross as `Gross[inC_Gross]`, c.tblCert_Number as `Prev. Cert#`,
c.tblCert_Gross as `Prev Gross[inC_Prev]`
FROM hilmark.tblcertificates_j c LEFT JOIN
(SELECT max(c.tblCert_ID) as MaxCertID, c.tblCert_XID456 as MaxSubbie,
c.tblCert_XIDJob as MaxPlot
FROM hilmark.tblcertificates_j c
GROUP BY c.tblCert_XIDJob
) cmax
WHERE cmax.MaxCertID = c.tblCert_ID AND cmax.MaxPlot = c.inPlot_ID AND cmax.MaxSubbie = c.inSubbie;
Some notes:
I doubt this really does what you want, because MaxSubbie has an indeterminate value. But you save the query works. Why do you need both comparisons?
When using table aliases, make them abbreviations for the table so the query is easier to read.
Only use single quotes for string and date constants.