根据某种条件查询表A或表B

编程问答 2022-06-08

问题描述

在Oracle DB（12）中，我有2个表：

表：STEP_DETAILS 

+-----------+---------+---------------+
| record_id | step_id | material_type |
+===========+=========+===============+
| 1         | 1       | in            |
+-----------+---------+---------------+
| 2         | 1       | in            |
+-----------+---------+---------------+
| 3         | 1       | out           |
+-----------+---------+---------------+
| 4         | 2       | in            |
+-----------+---------+---------------+
| 5         | 2       | out           |
+-----------+---------+---------------+
| 6         | 2       | out           |
+-----------+---------+---------------+

表：ACTIONS_DETAILS 

+-----------+-----------+---------------+
| record_id | action_id | material_type |
+===========+===========+===============+
| 1         | 11        | in            |
+-----------+-----------+---------------+
| 2         | 11        | out           |
+-----------+-----------+---------------+
| 3         | 12        | in            |
+-----------+-----------+---------------+
| 4         | 12        | out           |
+-----------+-----------+---------------+

所有id列均为INTEGER类型。

我需要计算两个表的输入材料。 在PL / SQL块中，我具有以下功能，每个功能都具有“几乎”相同的查询：

--count from step_details:
FUNCTION get_step_input_count(p_step_id  step_details.step_id%TYPE)
  RETURN INTEGER
  IS
    l_count INTEGER := 0;
  BEGIN
    SELECT COUNT(1)
      INTO l_count
      FROM step_details
     WHERE step_id = p_step_id
       AND material_type = 'in';

    RETURN l_count;
  END get_step_input_count;

--count from action_details:
  FUNCTION get_action_input_count(p_action_id  action_details.action_id%TYPE)
  RETURN INTEGER
  IS
    l_count INTEGER := 0;
  BEGIN
    SELECT COUNT(1)
      INTO l_count
      FROM action_details
     WHERE action_id = p_action_id
       AND material_type = 'in';

    RETURN l_count;
  END get_action_input_count;

有可能编写一个单一的SELECT语句，该语句可以根据某种条件每次查询2个表之一，因此我最终将编写一个使用一个查询而不是2个函数的函数，例如：

  FUNCTION get_input_count(p_parent_id  integer,p_from       varchar2)
  RETURN INTEGER
  IS
    l_count INTEGER := 0;
  BEGIN
    SELECT COUNT(1)
      INTO l_count
      FROM (when p_from = 'S' then 'step_details'
            when p_from = 'A' then 'action_details')
     WHERE (when p_from = 'S' then 'step_id   = p_parent_id'
            when p_from = 'A' then 'action_id = p_parent_id')
       AND material_type = 'in';

    RETURN l_count;
  END get_input_count;

解决方法

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