精讲MySQL 数据库的 SQL 语法参考_MySQL
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
...); "Ei\x0
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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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