instance method unique_constraints

# File activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb, line 726
        def unique_constraints(table_name)
          scope = quoted_scope(table_name)

          unique_info = internal_exec_query(<<~SQL, "SCHEMA", allow_retry: true, materialize_transactions: false)
            SELECT c.conname, c.conrelid, c.condeferrable, c.condeferred, pg_get_constraintdef(c.oid) AS constraintdef,
            (
              SELECT array_agg(a.attname ORDER BY idx)
              FROM (
                SELECT idx, c.conkey[idx] AS conkey_elem
                FROM generate_subscripts(c.conkey, 1) AS idx
              ) indexed_conkeys
              JOIN pg_attribute a ON a.attrelid = t.oid
              AND a.attnum = indexed_conkeys.conkey_elem
            ) AS conkey_names
            FROM pg_constraint c
            JOIN pg_class t ON c.conrelid = t.oid
            JOIN pg_namespace n ON n.oid = c.connamespace
            WHERE c.contype = 'u'
              AND t.relname = #{scope[:name]}
              AND n.nspname = #{scope[:schema]}
          SQL

          unique_info.map do |row|
            columns = decode_string_array(row["conkey_names"])

            nulls_not_distinct = row["constraintdef"].start_with?("UNIQUE NULLS NOT DISTINCT")
            deferrable = extract_constraint_deferrable(row["condeferrable"], row["condeferred"])

            options = {
              name: row["conname"],
              nulls_not_distinct: nulls_not_distinct,
              deferrable: deferrable
            }

            UniqueConstraintDefinition.new(table_name, columns, options)
          end
        end