Home Database Mysql Tutorial 精讲MySQL 数据库的 SQL 语法参考_MySQL

精讲MySQL 数据库的 SQL 语法参考_MySQL

Jun 01, 2016 pm 02:03 PM
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一、资料定义 ddl(data definition language) W!}{ud?D  
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  资料定语言是指对资料的格式和形态下定义的语言,他是每个资料库要建立时候时首先要面对的,举凡资料分哪些表格关系、表格内的有什麽栏位主键、表格和表格之间互相参考的关系等等,都是在开始的时候所必须规划好的。 g&z 0I-vD  
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  1、建表格: ^|5'0~l/.  
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create table table_name( sZM c-  
column1 datatype [not null] [not null primary key], :KZt]*mO.  
column2 datatype [not null], -9JZ`X 
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  说明:  $baT~  
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datatype --是资料的格式,详见表。 $_Mz*UYC  
nut null --可不可以允许资料有空的(尚未有资料填入)。 TVu ]-;  
primary key --是本表的主键。 rxSWd  
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  2、更改表格  f'@3`i@fz  
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alter table table_name gw6O|DuC  
add column column_name datatype W so  
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  说明:增加一个栏位(没有删除某个栏位的语法。 :;PJ`+*ru  
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alter table table_name dFKsQEF3"_  
add primary key (column_name) |?/zk  
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  说明:更改表得的定义把某个栏位设为主键。 hj\bDz  
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alter table table_name Y_ZH"7@  
drop primary key (column_name) \,}Vb-x(  
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  说明:把主键的定义删除。 W DsCzJHQ  
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  3、建立索引  |;-

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