Rules for repeated LOAD statements against same data

[tschullo]

I'm wondering if someone could point me to a clear discussion of the rules for loading data using multiple load statements to add fields to the initial load.

For example:

Table1

EmplID   Year     CourseName      EmpYear_KEY

101         2017     QV101                1

101         2017     QV102                1

102         2017     QV101                2

Table2

EmplID    Country      HireDate

101           US             2/4/2016

102           UK             2/4/2017

HourReqs:

// <------------------------------------------------------------------------------------- Insert point #1

// First I need a distinct list of Employee/Yr combinations.

// I will use the EmpYear_KEY to link to Table1 but need the fields for next steps...

LOAD Distinct EmplID,

           Year,

           EmpYear_KEY

Resident table1;

//Next I tack on the country and Hire Date

Left Join(Table1)

LOAD EmplID,

Country as EmplCtry,

HireDate as [Hire Date]

Resident Table2;

//Now I would like to calculate some new fields

Ideally, I could add some code like this at "Insert point #1" above:

LOAD *,
Ceil(ReqHrsFactor*FullYearReqdHrs) as [Required Hours];

LOAD *,
if(Year([Hire Date])<Year,1,
if(Year([Hire Date])>Year,0,
DayNumberOfYear([Hire Date])/366)) as ReqHrsFactor, For pro-rated reqd hrs factor
If(EmplCtry = 'US',56,ApplyMap('GCA_OverrideMap',[Employee ID],35)) as FullYearReqdHrs;

But that didnt't work so i think I'm going to have to continue to do more joins on itself or use another table.

I just would like to better understand what the rules are around mutliple calls to LOAD for same set of data.