Change foreign key constraints to point to a different table

generate-alter-tables.sql

-- PostgreSQL
SELECT
  'ALTER TABLE ' || source_tbl.relname || ' ' ||
  'DROP CONSTRAINT '|| constr.conname ||'; ' ||
  'ALTER TABLE ' || source_tbl.relname || ' ' ||
  'ADD CONSTRAINT ' || constr.conname || ' ' ||
  'FOREIGN KEY (' || source_col.attname || ') ' ||
  'REFERENCES new_table_name (primary_key_name);'
FROM pg_constraint constr
INNER JOIN pg_class target_tbl ON constr.confrelid = target_tbl.oid
INNER JOIN pg_attribute target_col ON target_tbl.oid = target_col.attrelid
INNER JOIN pg_class source_tbl ON constr.conrelid = source_tbl.oid
INNER JOIN pg_attribute source_col ON source_tbl.oid = source_col.attrelid
WHERE target_tbl.relname = 'target_table_name'
AND target_col.attname = 'primary_key_name'
AND source_col.attnum = constr.conkey[1];

-- Outputs the following statements for all foreign key constraints that refer
-- target_table_name (primary_key_name):
--   ALTER TABLE source_table_name DROP CONSTRAINT old_constraint_name;
--   ALTER TABLE source_table_name 
--     ADD CONSTRAINT old_constraint_name
--     FOREIGN KEY (referencing_column_name) REFERENCES new_table_name (primary_key_name);