SELECT 语句用于从表中选取数据。
结果被存储在一个结果表中(称为结果集)。
SELECT 列名称 FROM 表名称
以及:
SELECT * FROM 表名称
注释:SQL 语句对大小写不敏感。SELECT 等效于 select。
创建表Persons
CREATE TABLE Persons(
Id_P INT NOT NULL,
LastName VARCHAR (20) NOT NULL,
FirstName VARCHAR (20) NOT NULL,
Address CHAR (25),
City CHAR (25),
PRIMARY KEY (Id_P)
);
INSERT INTO Persons (Id_P,LastName,FirstName,Address,City) VALUES(1,‘Adams‘,‘John‘,‘Oxford Street‘,‘London‘);
INSERT INTO Persons (Id_P,LastName,FirstName,Address,City) VALUES(2,‘Bush‘,‘George‘,‘Fifth Avenue‘,‘New York‘);
INSERT INTO Persons (Id_P,LastName,FirstName,Address,City) VALUES(3,‘Bush‘,‘Carter‘,‘Thomas‘,‘Changan Street‘);
1.我们希望从表中选取所有的列:
SELECT *
FROM Persons;
mysql> SELECT * FROM Persons;
+------+----------+-----------+---------------+----------------+
| Id_P | LastName | FirstName | Address | City |
+------+----------+-----------+---------------+----------------+
| 1 | Adams | John | Oxford Street | London |
| 2 | Bush | George | Fifth Avenue | New York |
| 3 | Bush | Carter | Thomas | Changan Street |
+------+----------+-----------+---------------+----------------+
3 rows in set (0.07 sec)
提示:星号(*)是选取所有列的快捷方式。
2.如果选取其中的列,如,LastName FirstName
select LastName , FirstName from Persons;
mysql> select LastName , FirstName from Persons;
+----------+-----------+
| LastName | FirstName |
+----------+-----------+
| Adams | John |
| Bush | George |
| Bush | Carter |
+----------+-----------+
3 rows in set (0.00 sec)
3.对于查询出来的结果说明:
在工作中,我们老大多次强调数据集的概念,查询出来的数据就是一个数据集,result-set
原文:http://www.cnblogs.com/yejibigdata/p/6372016.html