[英]How to ALTER TABLE to add CHECK constraint?
I want to ALTER my already created ZIPCODE table so that the sales_tax_applied field can never have a negative value. 我想更改已经创建的ZIPCODE表,以使sales_tax_applied字段永远不会具有负值。 Here is the code for my already created table:
这是我已经创建的表的代码:
CREATE TABLE ZIPCODE
(
city VARCHAR(50) NOT NULL,
state CHAR(2) NOT NULL,
zipcode VARCHAR(20) NOT NULL,
sales_tax_applied DECIMAL(10,4) NOT NULL,
PRIMARY KEY (zipcode)
);
What is the code for me to be able to do this? 我能够执行此操作的代码是什么? NOTE: all fields must be NOT NULL.
注意:所有字段都不能为空。
Thank you 谢谢
You would do: 您可以这样做:
alter table zipcode add constraint chk_zipcode_sales_tax_applied
check (sales_tax_applied >= 0);
You can also add this into the create table statement in multiple ways, such as: 您还可以通过多种方式将其添加到create table语句中,例如:
CREATE TABLE ZIPCODE (
city VARCHAR(50) NOT NULL,
state CHAR(2) NOT NULL,
zipcode VARCHAR(20) NOT NULL,
sales_tax_applied DECIMAL(10,4) NOT NULL,
PRIMARY KEY (zipcode),
constraint chk_zipcode_sales_tax_applied check (sales_tax_applied >= 0)
);
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