#MYSQL CREATE TABLE IN DATABASE UPDATE#
A foreign key constraint prevents the UPDATE and DELETE statement that breaks the link between two tables. A table can have one or more foreign keys. The foreign key of any table refers to the Primary Key of another table. First, create a new table named items with an integer column as the primary key: CREATE TABLE items ( itemid INT AUTOINCREMENT PRIMARY KEY, itemtext VARCHAR ( 255 ) ) Code language: SQL (Structured Query Language) (sql) You can use either INT or INTEGER in the CREATE TABLE statement above because they are interchangeable.
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. We can create one primary key in a table. Create a MySQL Table Using MySQLi and PDO The CREATE TABLE statement is used to create a table in MySQL. 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. DEFAULT: The DEFAULT constraint inserts a default value.Note: The CREATE TABLE command exists for almost all the relational databases like MySQL, Postgres, SQL Server, etc. 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. CREATE TABLE command is a part of the DDL (Data Definition Language) set of commands in MySQL and it allows a user to create a new table for the given database.
UNIQUE: This constraint ensures that the query inserts only unique values in the column on which the constraint has been created.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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