Question

在PostgreSQL中，我想通过引用列号来动态访问ROWTYPE中的列。

例如，我想访问第59列，例如r.column(59)，而不是r.columnname。这可能吗？

目的是我希望循环遍历多个列，并且不想对所有列进行硬编码。

例如：

r data.stageing_table%rowtype;

FOR r IN SELECT * FROM data.stage_table LOOP
   INSERT INTO TABLE XXX
   .....
   VALUES(r.column(8))

END LOOP

是否可以访问我的rowtype结果集中的列？

Answer 1

AFAIK你不能，但你可以做一些可能足够接近的事情。您可以获取关系中列的位置，并将其别名为该数字（以非数字字符为前缀）。您必须将变量声明为record。

pg_attribute系统表上的示例：

DO $$
DECLARE
  l_row record;
  l_query text := $q$ SELECT %s
                        FROM pg_attribute
                       WHERE attrelid = 'pg_attribute'::regclass
                  $q$;
BEGIN
  FOR l_row IN EXECUTE format(l_query, --below is value that goes into %s placeholder
                              (SELECT string_agg(concat(attname, ' AS c', attnum), ', ')
                                 FROM pg_attribute
                                WHERE attrelid = 'pg_attribute'::regclass
                                  AND attnum > 0)
                             )
  LOOP
    RAISE NOTICE 'Attname: % is column number %', l_row.c2, l_row.c6;
  END LOOP;
END;
$$;

实际执行的查询是：

SELECT attrelid AS c1, attname AS c2, atttypid AS c3, attstattarget AS c4,
       attlen AS c5, attnum AS c6, attndims AS c7, attcacheoff AS c8,
       atttypmod AS c9, attbyval AS c10, attstorage AS c11, attalign AS c12,
       attnotnull AS c13, atthasdef AS c14, attidentity AS c15, attisdropped AS c16,
       attislocal AS c17, attinhcount AS c18, attcollation AS c19, attacl AS c20,
       attoptions AS c21, attfdwoptions AS c22
  FROM pg_attribute
 WHERE attrelid = 'pg_attribute'::regclass

您可以从pg_attribute表中获取总列数，记住那些具有attnum＆lt; 0是隐藏系统列，因此不要对它们进行计数。我想您可以将max(attnum)或l_columns := array_agg(concat(attname, ' AS c', attnum), ', ');然后array_length(l_columns,1)用于计数，并array_to_string(l_columns,', ')获取动态SQL的列列表。

引用ROWTYPE表中的列

1 个答案: