oracle 行转列的demo

下面是一个示例，演示如何使用 Oracle SQL 将行转换为列：

假设有一个名为 "employees" 的表，其中包含以下列：employee_id, task_name, task_status。

-- 创建示例表
CREATE TABLE employees (
  employee_id NUMBER,
  task_name VARCHAR2(100),
  task_status VARCHAR2(20)
);

-- 插入示例数据
INSERT INTO employees VALUES (1, 'Task 1', 'Completed');
INSERT INTO employees VALUES (1, 'Task 2', 'Pending');
INSERT INTO employees VALUES (1, 'Task 3', 'Completed');
INSERT INTO employees VALUES (2, 'Task 1', 'Pending');
INSERT INTO employees VALUES (2, 'Task 2', 'Completed');
INSERT INTO employees VALUES (2, 'Task 3', 'Pending');

-- 使用行转列查询
SELECT
  employee_id,
  MAX(CASE WHEN task_name = 'Task 1' THEN task_status END) AS task1_status,
  MAX(CASE WHEN task_name = 'Task 2' THEN task_status END) AS task2_status,
  MAX(CASE WHEN task_name = 'Task 3' THEN task_status END) AS task3_status
FROM employees
GROUP BY employee_id;

上述查询会将每个员工的任务状态转换为列，输出结果如下：

EMPLOYEE_ID | TASK1_STATUS | TASK2_STATUS | TASK3_STATUS
--------------------------------------------------------
1            | Completed    | Pending      | Completed
2            | Pending      | Completed    | Pending

请注意，此示例使用了 CASE 表达式和聚合函数 MAX，以将每个任务名称的状态转换为单独的列。你可以根据自己的需求修改列名和条件。