根据某些条件查询表A或表B

Question

在 Oracle DB (12) 中，我有 2 个表：

表格：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 列都是 INTEGER 类型。

我需要计算两个表的输入材料。 在 PL/SQL 块中，我有以下函数，每个函数都有“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;

是否可以编写一个单独的 SELECT 语句，每次可以根据某些条件查询 2 个表之一，所以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;

Answer 1

您可以尝试以下方法：

select sum(num_rows)
from
(
    select count(*) as num_rows
    from tab1                        /* first table */
    where :param = 1
    union all
    select count(*) as num_rows
    from tab2                        /* second table */
    where :param = 2 
)

在这里，您使用单个 select 包装来自所有可能表的查询的 UNION ALL；每个表都会根据某个参数的值给出其贡献与否，因此您只能根据参数值从表中获取所需的行。

Answer 2

一种选择是使用由表名和列名的连接组成的动态 SQL，以及用于从每个表中查询的通用值的绑定变量 (p_parent_id)。

SQL> CREATE OR REPLACE FUNCTION get_input_count(p_parent_id INT, p_from VARCHAR2) RETURN INT IS
    l_count INT;
    crs     SYS_REFCURSOR;
    v_sql   VARCHAR2(32767);
    v_from  VARCHAR2(32);
    v_col   VARCHAR2(99);
BEGIN
    SELECT DECODE(p_from,'A','actions_details','S','step_details'),
           DECODE(p_from,'A','action_id','S','step_id')
      INTO v_from, v_col
      FROM dual;

     v_sql := 'SELECT COUNT(*) 
                 FROM '||v_from||' 
                WHERE material_type = ''in'' AND '||v_col||' = :prt_id';

     OPEN crs FOR v_sql USING p_parent_id; 
     LOOP       
        FETCH crs INTO l_count;
       EXIT WHEN crs%NOTFOUND;             
     END LOOP;

     CLOSE crs;

    RETURN l_count;
END;
/

Demo

在哪里

• 用零初始化l_count变量的值是多余的， 因为查询将无一例外地返回零，只要没有 找到匹配记录
• 关键字FUNCTION 应该在前面加上CREATE [OR REPLACE]
• 以名称结束存储的函数是可选的（可能是 忽略）

Answer 3

您还可以使用如下所示的动态 SQL。 在这种情况下应该注意 SQL 注入。

sql_statement := 'select count(*)';
IF table = 'xxx'
THEN 
  sql_statement := sql_statement || ' from xxx where material_type = ''in''';
ELSIF table = 'yyy'
  sql_statement := sql_statement || ' from yyy where yyyy_type = ''in''';
END IF;
sql_statement := sql_statement blur blur;
EXECUTE IMMEDIATE sql_statement INTO l_count USING p_1;