![]() Now, let us create a table named tblPatient with NOT NULL constraint. CREATE TABLE dsttbl ( id INT NOT NULL AUTOINCREMENT, PRIMARY KEY (id) ) SELECT a, b, c FROM srctbl. A foreign key constraint prevents the UPDATE and DELETE statement that breaks the link between two tables. Selection from MySQL Cookbook, 2nd Edition Book. A table can have one or more foreign keys. The foreign key of any table refers to the Primary Key of another table. FOREIGN KEY: The foreign key is a column that creates a link between two tables.When we create a primary key, a clustered index will be created automatically. In this case (because bar1 can be NULL) innodb will create its internal primary key which is not exposed on the top level. We can create one primary key in a table. The primary key contains unique values and cannot contain a NULL value. The primary key consists of one or more columns. Following are the characteristics of the Primary key PRIMARY KEY: The Primary key constraint is used to identify each record uniquely.If we do not specify the values for the column on which the default constraint, it inserts the default value specified in the DEFAULT constraints. Consider the partitioned table created as shown here: mysql> CREATE TABLE tnopk (c1 INT, c2 INT) -> PARTITION BY RANGE (c1) ( -> PARTITION p0 VALUES LESS THAN (10), -> PARTITION p1 VALUES LESS THAN (20), -> PARTITION p2 VALUES LESS THAN (30), -> PARTITION p3 VALUES LESS THAN (40) -> ) Query OK, 0 rows affected (0. DEFAULT: The DEFAULT constraint inserts a default value.CHECK: When we insert a record in a table, the check constraint ensures that the values that we are inserting in a column must satisfy the condition specified in a CHECK constraint.However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table. ![]() UNIQUE: This constraint ensures that the query inserts only unique values in the column on which the constraint has been created. A PRIMARY KEY constraint automatically has a UNIQUE constraint.NOT NULL: This constraint ensures that a query does not insert a NULL value in a column on which the constraint has been created.A table can have the following constraints. Now, let us understand how we can create a table with a constraint. The above command creates a table named tblPatient in Patients schema. ![]()
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