mysql中的as语句

SELECT * FROM original_table AS t;

SELECT original_column AS col FROM original_table;

SELECT t1.column1 AS col1, t2.column2 AS col2
FROM table1 AS t1
JOIN table2 AS t2 ON t1.id = t2.id;

SELECT t1.column1, (SELECT t2.column2 AS col2 FROM table2 AS t2 WHERE t2.id = t1.id) AS subquery_result
FROM table1 AS t1;

SELECT COUNT(*) AS total_count, AVG(column1) AS avg_value
FROM original_table;

-- 创建示例表
CREATE TABLE employees (
    id INT PRIMARY KEY,
    first_name VARCHAR(50),
    last_name VARCHAR(50),
    salary DECIMAL(10, 2)
);

-- 插入示例数据
INSERT INTO employees (id, first_name, last_name, salary)
VALUES (1, 'John', 'Doe', 50000),
       (2, 'Jane', 'Smith', 60000),
       (3, 'Mike', 'Johnson', 55000);

-- 使用AS语句查询数据并指定别名
SELECT first_name AS fname, last_name AS lname, salary AS sal
FROM employees;