Update records by joining local and foreign db using db link - sql-update

Question

t - current db table
table1 - other db
database - current db table where the "other db" credentials are stored
SELECT
t.*
FROM "database" d, t,
dblink_exec(
format('dbname = %s host = %s port = %s user = %s password = %s', databasename, servername, port, username, "password"),
format('UPDATE
table1 a
SET
(col1, col2) = (SELECT
%L :: json, now()
FROM t b -- t is the local table (from current db)
WHERE b.col2 = a.col2
AND b.col3 = a.col3
AND b.col4 = a.col4)
WHERE a.col2 = ''ABC''
AND a.col3 = ''DEF''
', data )) -- column data is from table ```t```
WHERE databasename = 'otherdb';
How to update the records by joining local table to other db. I need the table t to stick in the correct place. I can't run this on other db as there are other dependencies (mostly timing).

Answer 1

I was able to achieve this by JOINING the tables first and form the UPDATE statement and feed the UPDATE statement to the dblink_exec.
SELECT
dblink_exec(
format('dbname = %s host = %s port = %s user = %s password = %s', databasename, servername, port, username, "password"),
format ('UPDATE table1 %1$sSET col4 = %3$L :: json, %2$scol3 = now() %1$sWHERE col3 = %4$L %2$sAND col3 = ''ABC'' %2$sAND col2 = ''DEF'';',
E'\n',
E'\n\t',
t.data,
t.col3
)
)
FROM t
INNER JOIN
(
SELECT x.*
FROM "database" d,
dblink(
format('dbname = %s host = %s port = %s user = %s password = %s',
databasename, servername, port, username, "password"
),
'SELECT
*
FROM table1
WHERE col1 = ''ABC''
AND col2 = ''DEF''
'
) AS x( col1 TEXT,
col2 TEXT,
col3 TEXT,
col4 TEXT
)
WHERE databasename = 'otherdb'
) as otherdb
CROSS JOIN "database" d
ON otherdb.col1 = t.col1
AND otherdb.col2 = t.col2
AND otherdb.col1 = 'DEF'
AND otherdb.col2 = 'ABC'
WHERE databasename = 'otherdb';