Обсуждение: [GENERAL] updating dup row

how can I update a row with newest id from another table if it exists somewhere else?

Example:

table test1

• id (primary key)
• id_user_bill
• clientid

table test2

• item_id
• userid (there are duplicated rows here)
• clientid
• id (primary key)

-- finding the dup records

INSERT INTO test2_results 

SELECT 

item_id,

userid

count(*) as dup_count,

MAX(id) as recent_id

FROM

test2

GROUP BY 

item_id,

userid

HAVING COUNT(*) > 1;

if test1.id_user_bill = test2.id, then

update test1.id_user_bill with test2_results.recent_id

UPDATE test1 SET test1.id_user_bill = test2_results.recent_id FROM test2_results WHERE test1.id_user_bill = test2_results.item_id;

(at least if I interpret what you're asking correctly, there's some errors there, for instance, there's no such field as test2.id shown, and the schema of test2_results is undefined, too)

'from' works very much like a INNER JOIN, and the WHERE clause has to include the join condition.

-- 
john r pierce, recycling bits in santa cruz