Need help with update statement with multiple joins

Question

I've got the following select statement that is pulling 29 records:
SELECT
PPA.PROJECT_ID,
PPA.SEGMENT1,
peia.expenditure_item_id,
peia.expenditure_type,
pec.expenditure_comment
FROM PA.PA_PROJECTS_ALL PPA,
pa.pa_expenditure_items_all peia,
pa.pa_expenditure_comments pec
where PPA.segment1 < '2008' and
PPA.project_id = 52 and -- just run for project # 20077119 for testing
peia.expenditure_type = 'PAYROLL' and
peia.project_id = ppa.project_id and
PEC.EXPENDITURE_ITEM_ID = PEIA.EXPENDITURE_ITEM_ID;
I need to update the pec.expenditure_comments to a static field for those 29 records. I assume I should start with the following, but not sure how to complete the where:
update
pa.pa_expenditure_comments pec
set pec.expenditure_comment = 'REFERENCE HD#728'
where
First time that we've ever needed to update, so any and all help appreciated.

Answer 1

Try using exists:
update pa.pa_expenditure_comments pec
set    pec.expenditure_comment = 'REFERENCE HD#728'
where exists ( select null
               from   pa.pa_projects_all ppa
               ,      pa.pa_expenditure_items_all peia
               ,      pa.pa_expenditure_comments pec2
               where  ppa.segment1 < ''    -- not sure what you posted here, so for next time:
                                           -- please put your examples between the code tags.
               and    ppa.project_id = 52  -- just run for project # 20077119 for testing
               and    peia.expenditure_type = 'PAYROLL'
               and    peia.project_id = ppa.project_id
               and    pec2.expenditure_item_id = peia.expenditure_item_id
               and    pec2.expenditure_item_id = pec.expenditure_item_id
             );