表的完整性約束
約束某一個字段
1. 無符號的
只和數字類型有關
int unsigned(unsigned這個關鍵字表示前面這個數字是無符號的)
create table t10(id int unsigned);
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2.不能爲空
not null
create table t11(
id int not null
);
如果既是無符號的,也是不能爲空,就直接在後面在寫就行了
create table t11