如何在oracle中根据空值将多行合并为一行

-- 假设您有一个名为employees的表，包含name和group_id字段
CREATE TABLE employees (
  id NUMBER,
  name VARCHAR2(100),
  group_id NUMBER
);

-- 插入一些示例数据
INSERT INTO employees (id, name, group_id) VALUES (1, 'Alice', 1);
INSERT INTO employees (id, name, group_id) VALUES (2, 'Bob', 1);
INSERT INTO employees (id, name, group_id) VALUES (3, 'Charlie', 2);
INSERT INTO employees (id, name, group_id) VALUES (4, NULL, 2);
INSERT INTO employees (id, name, group_id) VALUES (5, 'David', 2);

-- 查询以获取每个group_id的name列表，同时处理空值
SELECT 
  group_id,
  LISTAGG(COALESCE(name, 'NULL'), ', ') WITHIN GROUP (ORDER BY id) AS names
FROM employees
GROUP BY group_id;

GROUP_ID | NAMES
---------+-----------------------
       1 | Alice, Bob
       2 | Charlie, NULL, David