Oracle 26ai 的 SQL 语言增强特性

Oracle 26ai 的SQL 语言增强特性详细示例：

1. GROUP BY ALL 语法

用途：自动按 SELECT 列表中所有非聚合列分组，无需显式列出所有列。

sql 复制代码

-- 传统写法：需要显式列出所有非聚合列
SELECT department_id, job_id, AVG(salary) AS avg_sal
FROM employees
GROUP BY department_id, job_id;

-- 26ai 新写法：使用 GROUP BY ALL 自动包含所有非聚合列
SELECT department_id, job_id, AVG(salary) AS avg_sal
FROM employees
GROUP BY ALL;

适用场景：当 SELECT 列表有很多列时，简化代码并避免遗漏。

2. QUALIFY 子句（窗口函数过滤）

用途：直接过滤窗口函数的结果，无需嵌套子查询。

sql 复制代码

-- 传统写法：需要子查询或 CTE
WITH ranked AS (
    SELECT employee_id, first_name, salary,
           RANK() OVER (ORDER BY salary DESC) AS salary_rank
    FROM employees
)
SELECT * FROM ranked WHERE salary_rank <= 5;

-- 26ai 新写法：使用 QUALIFY 直接过滤
SELECT employee_id, first_name, salary,
       RANK() OVER (ORDER BY salary DESC) AS salary_rank
FROM employees
QUALIFY salary_rank <= 5;

-- 另一个示例：查找每个部门工资前 3 的员工
SELECT department_id, first_name, salary,
       ROW_NUMBER() OVER (PARTITION BY department_id ORDER BY salary DESC) AS rn
FROM employees
QUALIFY rn <= 3;

3. UUID() 函数（RFC 9562 版本 4）

用途：生成标准 UUID，替代手动生成或调用外部函数。

sql 复制代码

-- 生成单个 UUID
SELECT UUID() FROM dual;
-- 结果示例：550e8400-e29b-41d4-a716-446655440000

-- 插入数据时自动生成 UUID
CREATE TABLE users (
    user_id RAW(16) DEFAULT UUID() PRIMARY KEY,
    username VARCHAR2(50),
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

INSERT INTO users (username) VALUES ('zhangsan');
-- user_id 自动填充为 UUID

-- 批量生成 UUID
SELECT UUID() AS id, first_name 
FROM employees 
WHERE department_id = 10;

4. GROUP BY 支持列别名或位置编号

用途：使用 SELECT 列表中的别名或位置号进行分组，更简洁。

sql 复制代码

-- 传统写法：重复表达式或使用列名
SELECT SUBSTR(hire_date, 1, 4) AS hire_year, COUNT(*) AS cnt
FROM employees
GROUP BY SUBSTR(hire_date, 1, 4);

-- 26ai 新写法：使用列别名
SELECT SUBSTR(hire_date, 1, 4) AS hire_year, COUNT(*) AS cnt
FROM employees
GROUP BY hire_year;

-- 使用位置编号（从 1 开始）
SELECT department_id, job_id, AVG(salary) AS avg_sal
FROM employees
GROUP BY 1, 2;  -- 按第 1 列(department_id)和第 2 列(job_id)分组

-- 混合使用别名和位置编号
SELECT department_id, job_id, AVG(salary) AS avg_sal
FROM employees
GROUP BY 1, job_id;  -- 位置 1 和别名混用

5. 非位置 INSERT 子句（命名列插入）

用途：通过列名而非位置指定插入值，顺序无关，更清晰。

sql 复制代码

-- 传统写法：必须按列定义顺序，VALUES 顺序必须与列列表一致
INSERT INTO employees (employee_id, first_name, last_name, email, hire_date, job_id)
VALUES (207, 'John', 'Smith', 'jsmith', SYSDATE, 'IT_PROG');

-- 26ai 新写法：命名列插入，可以任意顺序指定
INSERT INTO employees (
    employee_id => 207,
    last_name => 'Smith',
    first_name => 'John',
    job_id => 'IT_PROG',
    email => 'jsmith',
    hire_date => SYSDATE
);

-- 批量插入时更清晰
INSERT ALL
    INTO employees (employee_id => 208, last_name => 'Wang', first_name => 'Wei', job_id => 'SA_REP')
    INTO employees (employee_id => 209, first_name => 'Li', last_name => 'Hua', job_id => 'MK_MAN')
SELECT 1 FROM dual;