sql check約束
Basically, CHECK constraint is used to LIMIT in columns for the range of values. We can use this constraint for single or multiple columns.
基本上， CHECK約束用于限制值范圍內的列 。 我們可以將此約束用于單列或多列。
In single column, CHECK allows LIMIT on some values in a column and in multiple columns, CHECK allows LIMIT on firm columns based in other column in the row on a table.
在單列中， CHECK允許對一列中的某些值進行限制，在多列中 ， CHECK允許對基于表中行中其他列的公司列進行LIMIT 。
如何在示例中使用CHECK？ (How to use CHECK with example?)
1) For single column
1)對于單列
CREATE TABLE Conpany
(E_Id int NOT NULL CHECK (E_Id>0),E_Name varchar(255) NOT NULL,
Contact number(10),Address varchar(255),City varchar(255));
2) For multiple Columns
2)對于多列
CREATE TABLE company
(E_Id int NOT NULL,E_Name varchar(255) NOT NULL,contact number(10),
Address varchar(255),City varchar(255),
CONSTRAINT chk_emp CHECK (E_Id>0 AND City='Gwalior'));
USE of ALTER to ADD CHECK constraint in an already created table
在已創建的表中使用ALTER來添加CHECK約束
1) For single column
1)對于單列
ALTER TABLE company ADD CHECK (E_Id>0);
2) For multiple columns
2)對于多列
ALTER TABLE company ADD CONSTRAINT chk_emp CHECK (E_Id>0 AND E_name='Bharti');
How to DROP CHECK constraint from a table?
如何從表中刪除檢查約束？
ALTER TABLE company DROP CONSTRAINT chk_emp;
Conclusion:
結論：
In this article, we have learnt what is CHECK constraint, How to use it with example and how we can alter and drop CHECk on a table?
在本文中，我們學習了什么是CHECK約束，如何在示例中使用它以及如何在表上更改和刪除CHECk？
翻譯自: https://www.includehelp.com/sql/CHECK-Constraint.aspx
sql check約束
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