How can we define constraint with user defined name?
Some CONSTRAINTS can be used along with the SQL CREATE TABLE statement. The general structure of the SQL CONSTRAINT is defined as: The CONSTRAINT keyword is followed by a constraint name followed by a column or a list of columns.
What do you mean by uniqueness constraints?
A unique constraint is a type of column restriction within a table, which dictates that all values in that column must be unique though may be null. To ensure that a column is UNIQUE and cannot contain null values, the column must be specified as NOT NULL.
How to get unique constraint column names in SQL?
USER_CONSTRAINTS would return foreign keys also. You need only primary and unique keys. But uniqueness can be achieved via unique index too. It won’t be shown in constraints list. You need to watch USER_INDEXES view. The good point is that primary and unique keys create corresponding unique indexes.
Can a unique constraint be a primary constraint?
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. However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table. SQL UNIQUE Constraint on CREATE TABLE
How to create unique constraint on persons table?
The following SQL creates a UNIQUE constraint on the “ID” column when the “Persons” table is created: To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax: To create a UNIQUE constraint on the “ID” column when the table is already created, use the following SQL:
How to determine the uniqueness of a constraint in MySQL?
MySQL uses the combination of values in both column column_name1 and column_name2 to evaluate the uniqueness. If you define a UNIQUE constraint without specifying a name, MySQL automatically generates a name for it. To define a UNIQUE constraint with a name, you use this syntax: [CONSTRAINT constraint_name] UNIQUE (column_list)