How do I remove a foreign key?
- In Object Explorer, expand the table with the constraint and then expand Keys.
- Right-click the constraint and then click Delete.
- In the Delete Object dialog box, click OK.
How do I delete a foreign key constraint in SQL?
- Expand your database view.
- Right Click on Table which has foreign key constraint. …
- Right click on the column which has the foreign key reference. …
- A list of relationships will appear (if you have one) in a pop up window.
- From there you can delete the foreign key constraint.
- Expand your database view.
- Right Click on Table which has foreign key constraint. …
- Right click on the column which has the foreign key reference. …
- A list of relationships will appear (if you have one) in a pop up window.
- From there you can delete the foreign key constraint.
Can we delete foreign key without deleting primary key?
What happens when you delete a foreign key?
Which clause is used to remove a foreign key constraint?
How do I create a constraint in MySQL?
The syntax for creating a unique constraint using an ALTER TABLE statement in MySQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column1, column2, … column_n); table_name.
How do you add constraints to a table?
Use the ADD CONSTRAINT clause to specify a primary key, foreign key, referential, unique, or check constraint on a new or existing column or on a set of columns. This syntax fragment is part of the ALTER TABLE statement. Notes: For NULL and NOT NULL constraints, use instead the MODIFY Clause.
What is a composite key in SQL?
A composite key in SQL can be defined as a combination of multiple columns, and these columns are used to identify all the rows that are involved uniquely. Even though a single column can’t identify any row uniquely, a combination of over one column can uniquely identify any record.
What is cascade in MySQL?
CASCADE : Delete or update the row from the parent table and automatically delete or update the matching rows in the child table. Both ON DELETE CASCADE and ON UPDATE CASCADE are supported.
How do I delete a parent table in MySQL?
ON DELETE CASCADE clause in MySQL is used to automatically remove the matching records from the child table when we delete the rows from the parent table. It is a kind of referential action related to the foreign key.
What is restrict in SQL?
RESTRICT : Rejects the delete or update operation for the parent table. Specifying RESTRICT (or NO ACTION ) is the same as omitting the ON DELETE or ON UPDATE clause. NO ACTION : A keyword from standard SQL. In MySQL, equivalent to RESTRICT .
How many types of keys are there in database design?
There are mainly 5 types of Keys, that can be mentioned in the database. Candidate Key – The minimal set of attributes which can uniquely identify a tuple is known as a candidate key.
How do you delete a database in MySQL?
Deleting a MySQL or MariaDB database
Use the command ‘SHOW DATABASES;’ in the mysql-console like in the example above. Now copy the name of the database you want to delete. To do delete a database you need the command ‘DROP DATABASE’. The syntax is similar to creating a database.
How do I change the unique key in MySQL?
Sometimes we want to add a unique key to the column of an existing table; then, this statement is used to add the unique key for that column. Following are the syntax of the ALTER TABLE statement to add a unique key: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE(column_list);
How do you change a column name?
To change a column name, enter the following statement in your MySQL shell: ALTER TABLE table_name RENAME COLUMN old_column_name TO new_column_name; Replace table_name , old_column_name , and new_column_name with your table and column names.
How do I delete SQL?
- DELETE FROM table_name WHERE condition;
- Example. DELETE FROM Customers WHERE CustomerName=’Alfreds Futterkiste’;
- DELETE FROM table_name;
- Example. DELETE FROM Customers;
- DELETE FROM table_name WHERE condition;
- Example. DELETE FROM Customers WHERE CustomerName=’Alfreds Futterkiste’;
- DELETE FROM table_name;
- Example. DELETE FROM Customers;
What is SQL Indexing?
A SQL index is used to retrieve data from a database very fast. Indexing a table or view is, without a doubt, one of the best ways to improve the performance of queries and applications. A SQL index is a quick lookup table for finding records users need to search frequently.
How do I create a subquery in SQL?
- Subqueries must be enclosed within parentheses.
- A subquery can have only one column in the SELECT clause, unless multiple columns are in the main query for the subquery to compare its selected columns.
- An ORDER BY command cannot be used in a subquery, although the main query can use an ORDER BY.
- Subqueries must be enclosed within parentheses.
- A subquery can have only one column in the SELECT clause, unless multiple columns are in the main query for the subquery to compare its selected columns.
- An ORDER BY command cannot be used in a subquery, although the main query can use an ORDER BY.
How do I set primary key in MySQL?
Following are the syntax of the ALTER TABLE statement to create a primary key in MySQL: ALTER TABLE table_name ADD PRIMARY KEY(column_list);
How do I create a foreign key in MySQL workbench?
To add a foreign key, click the last row in the Foreign Key Name list. Enter a name for the foreign key and select the column or columns that you wish to index by checking the column name in the Column list. You can remove a column from the index by removing the check mark from the appropriate column.
How do I drop a table in MySQL?
DROP TABLE MySQL Command Syntax. To remove a table in MySQL, use the DROP TABLE statement. The basic syntax of the command is as follows: DROP [TEMPORARY] TABLE [IF EXISTS] table_name [, table_name] [RESTRICT | CASCADE];