Bulk UPDATE table with WHERE clause that is variable

Question

I have a bunch of pairs of values [(foo1, bar1), (foo2, bar2), ...] and I want to do a bunch of updates of "set the 'foo' column to 'foo1' where the 'bar' column is 'bar1'".

I am doing this in Python with psycopg2. I could do executemany with the query UPDATE table SET foo = %s WHERE bar = %s, but that's a lot of little updates and would take mad long.

How can I do this easily and fast? Perhaps something with a temp table?

Postgres version 9.3.

Answer 1

UPDATE tbl t 
SET    foo = v.foo
FROM  (
   VALUES ('foo1'::text, 'bar1'::text), ('foo2', 'bar2'), ...
   ) v(foo, bar)
WHERE t.bar = v.bar;

Explicit type casts are only required in the first row of the values expression. text in the example - could be anything. String literal in subsequent rows are coerced to the same types.

Depending on the form you have the key-value pairs, other methods may be more convenient. Like: create a temporary table, COPY to it, then use the temp table in the UPDATE like any other table. Details:

• How to update selected rows with values from a CSV file in Postgres?

Or you can pass two simple arrays and unnest in parallel (syntax for Postgres 9.3):

UPDATE tbl t 
SET    foo = v.foo
FROM  (
   SELECT unnest('{foo1,foo2,...}'::text[]) AS foo
        , unnest('{bar1,bar2,...}'::text[]) AS bar
   ) v(foo, bar)
WHERE t.bar = v.bar;

Postgres 9.4 has a better way:

• Is there something like a zip() function in PostgreSQL that combines two arrays?