CREATE TABLE claim_headers (amount_claimed INT, claim_header_id VARCHAR)
CREATE TABLE claims_documents (claim_id VARCHAR, created_date VARCHAR)

Find the total amount claimed in the most recently created document.
SELECT SUM(t1.amount_claimed) FROM claim_headers AS t1 JOIN claims_documents AS t2 ON t1.claim_header_id = t2.claim_id WHERE t2.created_date = (SELECT created_date FROM claims_documents ORDER BY created_date LIMIT 1)
SELECT SUM("t1"."amount_claimed") FROM "claim_headers" AS "t1" JOIN "claims_documents" AS "t2" ON "t1"."claim_header_id" = "t2"."claim_id" AND "t2"."created_date" = (SELECT "created_date" FROM "claims_documents" ORDER BY "created_date" NULLS FIRST LIMIT 1)