在 PL/SQL 过程中打开动态表名的游标

Question

我想创建一个使用游标的过程，这对于任意表都是一样的。我现在的样子是这样的：

create or replace
  PROCEDURE
    some_name(
      p_talbe_name IN VARCHAR2,
      p_chunk_size IN NUMBER,
      p_row_limit IN NUMBER
    ) AS

  CURSOR v_cur IS
     SELECT common_column,
       ora_hash(substr(common_column, 1, 15), p_chunk_size) as chunk_number
     -- Here it can find the table!
     FROM p_table_name;

  TYPE t_sample IS TALBE OF v_cur%rowtype;
  v_sample t_sample;
BEGIN
  OPEN v_cur;
  LOOP FETCH v_cur BULK COLLECT INTO v_sample LIMIT p_row_limit;
    FORALL i IN v_sample.first .. v_sample.last
    INSERT INTO chunks VALUES v_sample(i);
    COMMIT;
    EXIT WHEN v_cur%notfound;
  END LOOP;
  CLOSE v_cur;
END;

问题是它找不到我想要参数化的名为p_table_name 的表。问题是我需要基于存在于所有预期表中的common_column 的散列创建块。如何处理这个问题？也许有等效的 oracle 代码可以做同样的事情？然后我需要同样的查询效率。谢谢！

Answer 1

我会将其作为一个单独的 insert-as-select 语句来执行，只是因为您传入 table_name 的事实而变得复杂，因此我们需要使用动态 sql。

我会这样做：

CREATE OR REPLACE PROCEDURE some_name(p_table_name IN VARCHAR2,
                                      p_chunk_size IN NUMBER,
                                      p_row_limit  IN NUMBER) AS

  v_table_name VARCHAR2(32); -- 30 characters for the tablename, 2 for doublequotes in case of case sensitive names, e.g. "table_name"

  v_insert_sql CLOB;
BEGIN
  -- Sanitise the passed in table_name, to ensure it meets the rules for being an identifier name. This is to avoid SQL injection in the dynamic SQL
  -- statement we'll be using later.
  v_table_name := DBMS_ASSERT.ENQUOTE_LITERAL(p_table_name);

  v_insert_sql := 'insert into chunks (common_column_name, chunk_number)'||CHR(10)|| -- replace the column names with the actual names of your chunks table columns.
                  'select common_column,'||CHR(10)||
                  '       ora_hash(substr(common_column, 1, 15), :p_chunk_size) AS chunk_number'||CHR(10)||
                  'from   '||v_table_name||CHR(10)||
                  'where  rownum <= :p_row_limit';

  -- Used for debug purposes, so you can see the definition of the statement that's going to be run.
  -- Remove before putting the code in production / convert to proper logging code:
  dbms_output.put_line(v_insert_sql);

  -- Now run the statement:
  EXECUTE IMMEDIATE v_insert_sql USING p_chunk_size, p_row_limit;

  -- I've included the p_row_limit in the above statement, since I'm not sure if your original code loops through all the rows once it processes the
  -- first p_row_limit rows. If you need to insert all rows from the p_table_name into the chunks table, remove the predicate from the insert sql and the extra bind variable passed into the execute immediate.
END some_name;
/

通过使用单个 insert-as-select 语句，您正在使用最有效的工作方式。执行批量收集（您正在使用）会耗尽内存（将数据存储在数组中）并导致 PL/SQL 和 SQL 引擎之间的额外上下文切换，而 insert-as-select 语句可以避免。