join problem - Mailing list pgsql-sql

I have join problem:
"select i.ivid, v.eventdate, v.deposit, v.invdate, cai.db,                sum(i.tax) as tax,                sum(i.tax +
i.rowtot)as totalP,                (sum(i.tax + i.rowtot) - v.deposit) as balance              from invoice v
  left outer join                     invoiceitems i                on  v.ivid = i.ivid              where v.cusid =
$cusid                   and   v.cusid = cai.cusid                group by i.ivid,  v.eventdate, v.deposit, v.invdate,
cai.db
ERROR:  missing FROM-clause entry for table "cai"

If I add cai to the from clause "from invoice v, cai,  I get
ERROR:  missing FROM-clause entry for table "cai"
ERROR:  invalid reference to FROM-clause entry for table "v"

Where do I add the cai table reference???

thanks

-- 
Arthur R. Van Hook    Mayor - RetiredThe City of Lake Lotawana

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