@Column(columnDefinition）的使用

columnDefinition属性的使用：

@Table(name = "CUSTOMERS")@Entitypublic class Customer {    @Column(name = "ID")    @GeneratedValue(strategy = GenerationType.AUTO)    @Id    private Integer id;    @Column(name = "Name")    private String name;    @Column(name = "Email",columnDefinition="varchar(128) not null")    private String email;    @Column(name = "Age")    private int age;    ......}
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数据库DDL：

CREATE TABLE `customers` (  `ID` int(11) NOT NULL AUTO_INCREMENT,  `Age` int(11) DEFAULT NULL,  `Email` varchar(128) NOT NULL,  `Name` varchar(255) DEFAULT NULL,  PRIMARY KEY (`ID`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
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columnDefinition可以指定创建表时一些SQL语句，比如这里可以一次性指定，varchar长度128，且不能为空
当然，相同的结果可以通过nullable和length属性结合实现

@Table(name = "CUSTOMERS")@Entitypublic class Customer {    @Column(name = "ID")    @GeneratedValue(strategy = GenerationType.AUTO)    @Id    private Integer id;    @Column(name = "Name")    private String name;    @Column(name = "Email", nullable = true, length = 128)    private String email;    @Column(name = "Age")    private int age;    ......}
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数据库DDL：

CREATE TABLE `customers` (  `ID` int(11) NOT NULL AUTO_INCREMENT,  `Age` int(11) DEFAULT NULL,  `Email` varchar(128) DEFAULT NULL,  `Name` varchar(255) DEFAULT NULL,  PRIMARY KEY (`ID`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
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columnDefinition属性的特殊使用：
编程语言中字符串一般都用String表示，但是数据库中varcahr数值类型有长度限制，一旦需要大文本，则需要text数值类型
但是String类型默认映射的数值类型是varchar，columnDefinition可以进行额外指定

@Table(name = "CUSTOMERS")@Entitypublic class Customer {    @Column(name = "ID")    @GeneratedValue(strategy = GenerationType.AUTO)    @Id    private Integer id;    @Column(name = "Name")    private String name;    @Column(name = "Email", nullable = true, length = 128)    private String email;    @Column(name = "Age")    private int age;    @Column(name = "Remark",columnDefinition="text")    private String remark;    ......}
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数据库DDL：

CREATE TABLE `customers` (  `ID` int(11) NOT NULL AUTO_INCREMENT,  `Age` int(11) DEFAULT NULL,  `Email` varchar(128) DEFAULT NULL,  `Name` varchar(255) DEFAULT NULL,  `Remark` text,  PRIMARY KEY (`ID`)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
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remark列数值类型是text，而Name和Email默认是varcahr