传递表名作为plsql参数

Question

我想编写一个函数来返回一个表的行计数,该表的名称作为变量传入.这是我的代码:

create or replace function get_table_count (table_name IN varchar2)
  return number
is
  tbl_nm varchar(100) := table_name;
  table_count number;
begin
  select count(*)
  into table_count
  from tbl_nm;
  dbms_output.put_line(table_count);
  return table_count;
end;

我收到此错误:

FUNCTION GET_TABLE_COUNT compiled
Errors: check compiler log
Error(7,5): PL/SQL: SQL Statement ignored
Error(9,8): PL/SQL: ORA-00942: table or view does not exist

我理解这tbl_nm被解释为一个价值而不是一个参考,我不知道如何逃避这一点.

Answer 1

您可以使用动态SQL:

create or replace function get_table_count (table_name IN varchar2)
  return number
is
  table_count number;
begin
  execute immediate 'select count(*) from ' || table_name into table_count;
  dbms_output.put_line(table_count);
  return table_count;
end;

还有一种获取行数的间接方法(使用系统视图):

create or replace function get_table_count (table_name IN varchar2)
  return number
is
  table_count number;
begin
  select num_rows
    into table_count
    from user_tables
   where table_name = table_name;

  return table_count;
end;

第二种方法只有在调用此函数之前已在表上收集统计信息时才有效.