Nov 30, 2012 · CREATE TABLE TABLE_NAME ( eno NUMBER ,ename VARCHAR2(100) ,address VARCHAR2(2000) ,mobileno NUMBER NOT NULL ,constraint table_name_mobile_UK UNIQUE (mobileno) );

The UNIQUE constraint ensures that all values in a column are different. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint.

Apr 24, 2024 · By creating a unique constraint with NULL columns, we can ensure that non-NULL values are unique while allowing multiple rows with NULL values. In this article, We will explores how to create such a constraint in SQL, ensuring data integrity and consistency in database design and so on.

Sep 24, 2023 · You can use an in-line constraint for NOT NULL: CREATE TABLE BOOK_STORES ( Store_ID NUMBER(8) , Name VARCHAR2(30) NOT NULL , Contact VARCHAR2(30) , Rep_ID VARCHAR(5) , CONSTRAINT book_stores__Store_id__PK PRIMARY KEY (Store_ID) , CONSTRAINT book_stores__Name__UN UNIQUE (Name) );

Mar 29, 2019 · The first solution that would come to my mind is to add a deleted_at column with type TIMESTAMP and extend a constraint to (name, deleted_at). Let’s try it! ADD deleted_at TIMESTAMP NULL...

Constraints can be column level or table level. Column level constraints apply to a column, and table level constraints apply to the whole table. The following constraints are commonly used in SQL: NOT NULL - Ensures that a column cannot have a NULL value; UNIQUE - Ensures that all values in a column are different

Sep 18, 2024 · The syntax for creating a unique constraint with NULL columns in MySQL involves specifying the UNIQUE keyword during table creation or altering an existing table: CREATE TABLE table_name (column1 INT, column2 INT, UNIQUE KEY unique_constraint (column1, column2)); Examples of Unique Constraints with NULL columns in MySQL

Jun 16, 2017 · Suppose I have four columns | x | y | z | w | I would like the following constraint: If w is NULL, then x, y, z must be unique. If w is not NULL, then x, y, w must be unique. Is this possible?

Feb 8, 2017 · If you use a UNIQUE constraint but don't want multiple rows with NULL, declare the columns as NOT NULL and prohibit any row from having NULL. There are ways to implement a workaround using a trigger or with a generated column.

To define a UNIQUE constraint for a column when creating a table, you use the following syntax: ..., column1 datatype UNIQUE, ... In this syntax, you include the UNIQUE keyword in the definition of the column that you want to enforce the uniqueness.