sqlserver中起别名和添加列、修改列

/*
truncate table 表名(删除表中資料,和delete table 表名 是一樣的，效率
要比delete高，即删除速度比delete快)
*/
truncate table student4
SELECT * FROM dbo.student4
 
/*
起别名：2種方式
可以使用as關鍵字起别名
也可以用=來起别名
*/
SELECT *,stuAddress AS '位址' FROM student
SELECT *,stuAddress AS 位址 FROM student
SELECT  stu.*, '位址' = stu.stuAddress FROM student AS stu
SELECT stu.*,'位址' = stu.stuName + '籍貫在' + stu.stuAddress FROM student AS stu
UPDATE student SET stuAddress = '江西省贛州市' WHERE stuId = '9'
--添加列
ALTER TABLE student ADD hobby VARCHAR(30) NULL
ALTER TABLE student ADD schoolName VARCHAR(30) NULL
ALTER TABLE student ADD groupId VARCHAR(5)
--修改列
ALTER TABLE student ALTER COLUMN hobby VARCHAR(30) NULL
ALTER TABLE student ALTER COLUMN schoolName VARCHAR(25) NOT NULL
--
UPDATE student SET schoolName = '城關國小' WHERE stuId = '5'
UPDATE student SET schoolName = '' WHERE stuId = '5'
UPDATE student SET schoolName = NULL WHERE stuId = '1'
UPDATE student SET schoolName = 'null' WHERE stuId = '1'
--
SELECT * FROM student WHERE schoolName is NULL
SELECT * FROM student WHERE schoolName is NOT NULL
--常量列
SELECT *, 學校名稱 = schoolName, '城關國小' AS 國小名稱 FROM student 
SELECT *, 學校名稱 = schoolName, '實驗國小' AS '校名' FROM student 
/*
以下是一個sql的完整寫法
SELECT 
列名1 AS 别名,
列名2 AS 别名
FROM
表名
WHERE 
條件
GROUP BY
分組
HAVING
分組後的篩選
ORDER BY desc / asc
排序
*/