[英]primary key constraint in SQL queries
Why and what is the use of naming to a primary key constraint?为什么以及对主键约束进行命名有什么用?
create table users(
id int
, lastname varchar(255)
, firstname varchar(255)
, age int
, **constraint pk** primary key(id, lastname)
);
The purpose of naming a constraint is primarily so you can understand error messages when the constraint is violated.命名约束的目的主要是让您可以在违反约束时理解错误消息。
A secondary reason is for dropping the constraint.第二个原因是放弃约束。 It is much easier to find the constraint when it has a meaningful name.当约束具有有意义的名称时,它更容易找到约束。
That said, in tables that I create, the primary key is usually a synthetic key -- set automatically via auto_increment
for instance.也就是说,在我创建的表中,主键通常是合成键——例如通过auto_increment
自动设置。 And I don't drop primary key constraints.而且我不会放弃主键约束。 So I don't bother naming them.所以我懒得命名它们。
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