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 属于 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？

将quote_ident(r.relname)用作：

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 找到类似的东西。有没有更好的方法？

Answer 1

在 PL/pgSQL 中的 UPDATE 语句中，table 名称必须作为文字给出。如果要动态设置 table 名称和列，应使用 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]) || ' = , ' || 
                  quote_ident(r.cols_list[2]) || ' = ' ||
       ' WHERE ' || quote_ident(r.cols_list[1]) || ' =  AND ' ||
                    quote_ident(r.cols_list[2]) || ' = '
USING ncicd9, ncdesc, ocicd9, ocdesc;

USING子句只能用于替换数据值，如上所示。

Answer 2

你需要动态 SQL 和 EXECUTE 就像@Patrick 已经提供的那样。但是，您的函数和 EXECUTE 部分都可以 简单得多 。特别是，使用 format() 安全地连接更长的查询字符串（自 pg 9.1 起可用）：

CREATE OR REPLACE FUNCTION merge_children_of_icd9 (_ocicd9 text, _ocdesc text
                                                 , _ncicd9 text, _ncdesc text)
  RETURNS void AS
$func$
DECLARE
   _sql text;
BEGIN
   FOR _sql IN
      SELECT format('UPDATE %3$s SET %1$I =    , %2$I = 
                     WHERE           %1$I =  AND %2$I = '
                   , x.cols[1], x.cols[2], x.conrelid::regclass::text)
      FROM  (
         SELECT c.conrelid, array_agg(a.attname ORDER BY a.attnum) AS cols
         FROM   pg_constraint c
         JOIN   pg_attribute  a ON a.attrelid = c.conrelid
                               AND a.attnum = ANY(c.conkey)
         WHERE  c.confrelid = 'icd9'::regclass
         AND    c.contype = 'f'
         GROUP  BY c.oid, c.conrelid
         ORDER  BY c.oid
         ) x
   LOOP
   -- RAISE NOTICE '%', _sql;
      EXECUTE _sql
      USING   _ocicd9, _ocdesc, _ncicd9, _ncdesc;
   END LOOP;
END
$func$  LANGUAGE plpgsql;

如果 FK 约束未跨越至少两列或列的数据类型与 text 不兼容，则函数会出错。可能符合预期，也可能不符合预期。

关于如何安全传递标识符和执行动态的详细信息SQL:

Table name as a PostgreSQL function parameter
Define table and column names as arguments in a plpgsql function?

如何在函数的 UPDATE 或 SELECT 语句中使用动态列名？

How to use dynamic column names in an UPDATE or SELECT statement in a function?

sql

postgresql

parameter-passing

plpgsql

dynamic-sql