POSTGRESQL – complex updates

Fairly simple example: your file structure is as follows:

table1(parent_id)-> table2 (id)

table2(parent_id)-> table3(id).

table 1 links to table2 and table2 links to table3

For whatever reason table3 has to go. But  you want to update table1 with table3’s id.

so you’ve created a new column table3_id. (I know very bad naming convention but I’m hoping it aids the understanding of the solution)

update file1 set table3_id =


from table1

inner join table2 on ( = table1.parent_id  )

inner join table3 on ( = table2.parent_id ) )

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