sql - 如何在函数的 UPDATE 或 SELECT 语句中使用动态列名？

Question

在 PostgreSQL 9.1 中，PL/pgSQL，给定一个查询:

select fk_list.relname from ...

其中 relname 是 name 类型(例如，“table_name”)。

如何获得可直接在 UPDATE 语句中使用的“relname”的适当值:

Update <relname> set ...

在 PL/pgSQL 脚本中？

使用 quote_ident(r.relname) 作为:

Update quote_ident(r.relname) Set ...

失败:

syntax error at or near "(" LINE 55: UPDATE quote_ident(r.relname) ....

我正在使用的完整代码:

CREATE FUNCTION merge_children_of_icd9 (ocicd9 text, 
                      ocdesc text, ncicd9 text, ncdesc text)
RETURNS void AS $BODY$
DECLARE
  r RECORD;
BEGIN
  FOR r IN
    WITH fk_actions ( code, action ) AS (
      VALUES ('a', 'error'), 
             ('r', 'restrict'), 
             ('c', 'cascade'),
             ('n', 'set null'),
             ('d', 'set default')
    ), fk_list AS (
      SELECT pg_constraint.oid AS fkoid, conrelid, confrelid::regclass AS parentid,
             conname, relname, nspname,
             fk_actions_update.action AS update_action,
             fk_actions_delete.action AS delete_action,
             conkey AS key_cols
      FROM pg_constraint
      JOIN pg_class ON conrelid = pg_class.oid
      JOIN pg_namespace ON pg_class.relnamespace = pg_namespace.oid
      JOIN fk_actions AS fk_actions_update ON confupdtype = fk_actions_update.code
      JOIN fk_actions AS fk_actions_delete ON confdeltype = fk_actions_delete.code
      WHERE contype = 'f'
    ), fk_attributes AS (
      SELECT fkoid, conrelid, attname, attnum
      FROM fk_list
      JOIN pg_attribute ON conrelid = attrelid AND attnum = ANY(key_cols)
      ORDER BY fkoid, attnum
    ), fk_cols_list AS (
      SELECT fkoid, array_agg(attname) AS cols_list
      FROM fk_attributes
      GROUP BY fkoid
    )
    SELECT fk_list.fkoid, fk_list.conrelid, fk_list.parentid, fk_list.conname, 
           fk_list.relname, fk_cols_list.cols_list
    FROM fk_list
    JOIN fk_cols_list USING (fkoid)
    WHERE parentid = 'icd9'::regclass
  LOOP
    RAISE NOTICE 'now in loop. relname is %', quote_ident(r.relname);
    RAISE NOTICE 'cols_list[1] is %', quote_ident(r.cols_list[1]);
    RAISE NOTICE 'cols_list[2] is %', quote_ident(r.cols_list[2]);
    RAISE NOTICE 'now doing update';

    UPDATE quote_ident(r.relname) SET r.cols_list[1] = ncicd9, r.cols_list[2] = ncdesc
    WHERE r.cols_list[1] = ocicd9 AND r.cols_list[2] = ocdesc;

    RAISE NOTICE 'finished update'; 
  END LOOP;     
  RETURN;
END $BODY$ LANGUAGE plpgsql VOLATILE;   

-- select merge_children_of_icd9('', 'aodm type 2', '', 'aodm, type 2'); 

我敢肯定这种事情经常发生，但我似乎无法使用 PostgreSQL 找到类似的事情。有没有更好的办法？

Answer 1

在 PL/pgSQL 的 UPDATE 语句中，表名必须作为文字给出。如果你想动态设置表名和列，你应该使用 EXECUTE命令并将查询字符串粘贴在一起:

EXECUTE 'UPDATE ' || quote_ident(r.relname) ||
       ' SET ' || quote_ident(r.cols_list[1]) || ' = $1, ' || 
                  quote_ident(r.cols_list[2]) || ' = $2' ||
       ' WHERE ' || quote_ident(r.cols_list[1]) || ' = $3 AND ' ||
                    quote_ident(r.cols_list[2]) || ' = $4'
USING ncicd9, ncdesc, ocicd9, ocdesc;

USING 子句只能用于替换数据值，如上所示。