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check constraint in sql
Check-in SQL may be a database management system utilized to store and manage information. It is one of the foremost commonly utilized relational database management systems and is utilized in many different businesses for an assortment of purposes. It permits clients to create and manage databases and perform inquiries on the information put away within the database. Furthermore, it gives support for transactions, security, and other highlights. It is one of the foremost prevalent database systems and is utilized by numerous organizations over the world.
Check constraint on column level:
In the hospitality industry, check-in SQL can be used to determine the availability of hotel rooms. By running a query on the hotel’s database, the system can quickly determine which rooms are currently occupied and which are available. This can help the staff quickly check in new guests and avoid any confusion or double bookings.
CREATE TABLE table_name ( column1 datatype CONSTRAINT constraint_name CHECK (expression) );
The syntax above creates a table with a column-level check constraint. The CHECK keyword enforces a constraint on a column's values. The expression in the parentheses is evaluated for each row in the table and must return true for the row to be inserted or updated. If the expression returns false, the statement will fail, and the row will not be inserted or updated.
CREATE TABLE employees ( name varchar(255) CONSTRAINT age_check CHECK (age > 18) );
This statement creates a table called "employees" with a column called "name" of data type varchar(255). The check constraint "age_check" is also added, which requires that the value of the "age" column must be greater than 18 for each row.
Check constraint on table level:
CREATE TABLE TableName ( Column1 datatype, Column2 datatype, Column3 datatype, CONSTRAINT constraint_name CHECK (Column1 > 0) );
This statement creates a table named TableName with three columns, Column1, Column2, and Column3, each with its own data type. Additionally, a check constraint is added that requires that the value of Column1 must be greater than 0. This check constraint will be enforced whenever data is added to or updated in the table.
CREATE TABLE Employees ( EmployeeID int, Name varchar(255), Age int, CONSTRAINT AgeCheck CHECK (Age > 18) );
This creates a table named Employees with three columns (EmployeeID, Name, and Age) and a check constraint that requires Age to have a value greater than 18. The constraint is named AgeCheck.
Check constraint after table creation:
ALTER TABLE table_name ADD CONSTRAINT constraint_name CHECK (condition);
This statement will add a check constraint to the specified table. The condition specified in the CHECK clause will be evaluated for all values in the table. If the condition evaluates to false for any data value, the constraint is violated, and the statement will be rolled back.
ALTER TABLE Orders ADD CONSTRAINT chk_order_date CHECK (order_date > '2020-01-01');
This statement adds a check constraint to the Orders table, which checks that the order_date is greater than '2020-01-01'. If any existing order in the table has an order_date that is not greater than '2020-01-01', then the statement will be rolled back, and the constraint will not be applied.
Remove a check constraint
ALTER TABLE table_name DROP CONSTRAINT check_constraint_name;
The above ALTER TABLE statement removes a check constraint from an existing table. It requires the table's name and the check constraint's name to be dropped. Once executed, the check constraint will no longer be enforced on the table.
ALTER TABLE bookings DROP CONSTRAINT ck_booking_max_guests;
This ALTER TABLE statement will remove the check constraint named “ck_booking_max_guests” from the “bookings” table. After executing this statement, the check constraint will no longer be enforced, and bookings with more than 6 guests will be allowed.
The staff at the hospitality business used a check-in SQL query to determine the availability of hotel rooms quickly. This query allowed them to easily identify which rooms were occupied and which were available, allowing them to quickly check in new guests and avoid any confusion or double bookings. This efficient system provided a streamlined check-in process, ensuring guests were taken care of in no time.
1.What type of operation is used to add a new record to a table?
Answer: a. INSERT
2. Which of the following is used to specify the columns when using a SELECT statement?
Answer: d. COLUMN
3. How do you specify a condition in a WHERE clause?
Answer: a. By using comparison operators
4. Which statements are used to delete a record from a table?
Answer: c. DELETE