create table target
(
"id" serial primary key,
"title" varchar(50) not null,
"poster" varchar(100) default null
);
create table source
(
"id" serial primary key,
"posterId" serial REFERENCES target (id)
"poster" varchar(100) default null
);
INSERT INTO target ("poster")
SELECT "poster"
FROM source
WHERE source."posterId" = target.id