MySQL Data Types

1. value type

   type	Signed (SIGNED) value range	Unsigned (UNSIGNED) value range	size	describe
   TINYINT	(-128，127)	(0，255)	1byte	small integer value
   SMALLINT	(-32768，32767)	(0，65535)	2bytes	big integer value
   INT/INTEGER	(-2147483648，2147483647)	(0，4294967295)	4bytes	big integer value
   BIGINT(Long)	(-263，263-1)	(0，2^64-1)	8bytes	extremely large integer value
   FLOAT	(-3.402823466 E+38，3.402823466351 E+38)	0 sum (1.175494351 E-38, 3.402823466 E+38)	4bytes	single-precision floating-point value
   DOUBLE	(-1.7976931348623157 E+308， 1.7976931348623157 E+308)	0 Sum (2.2250738585072014E-308, 1.7976931348623157E+308)	8bytes	double-precision floating-point value
   DECIMAL				decimal value (exact)

   example:

   • user age field

     age tinyint unsigned
     

   • score 100

     score double(4,1)
     

2. string type

   type	size	describe
   CHAR	0-255 bytes	Fixed-length string (need to specify the length)
   VARCHAR	0-65535 bytes	Variable-length string (need to specify the length)
   BLOB	0-65 535 bytes	Long text data in binary form
   TEXT	0-65 535 bytes	long text data
   LONGTEXT	0-4 294 967 295 bytes	extremely large text data

   example:

   • gender

     gender char(1)
     

   • username

     username varchar(64)
     

3. datetime type

   type	Format	scope	size	describe
   DATE	YYYY-MM-DD	1000-01-01 to 9999-12-31	3	date value
   TIME	HH:MM:SS	-838:59:59 to 838:59:59	3	time value or duration
   YEAR	YYYY	1901 to 2155	1	year value
   DATETIME	YYYY-MM-DD HH:MM:SS	1000-01-01 00:00:00 to 9999-12-31 23:59:59	8	Mixed date and time values
   TIMESTAMP	YYYY-MM-DD	1970-01-01 00:00:01 to 2038-01-19 03:14:07	4	Mixed date and time values, timestamps

   example

   • Birthday

     birthday date
     

   • update time

     updatetime datetime
     

4. need

   需求：
   设计一张员工信息表，要求如下：
   	1. 编号（纯数字）
   	2. 员工工号 (字符串类型，长度不超过10位)
   	3. 员工姓名（字符串类型，长度不超过10位）
   	4. 性别（男/女，存储一个汉字）
   	5. 年龄（正常人年龄，不可能存储负数）
   	6. 身份证号（二代身份证号均为18位，身份证中有X这样的字符）
   	7. 入职时间（取值年月日即可）
   	
   create table employee(
   	id bigint comment '编号',
       workno varchar(10) comment '员工工号',
       name varchar(10) comment '员工姓名',
       gender char(1) comment '性别',
       age tinyint UNSIGNED  comment '年龄',
       idcard char(18) comment '身份证号',
       entryDate date comment '入职时间'
   )comment '员工表';