2/9/2024 0 Comments Create unique identifier sqlIn this article I'll present three methods for generating UUIDs.Īn alternatively to a UUID is the SYS_GUID() function provided by Oracle to produce a Globally Unique Identifier, their equivalent of a UUID. However, the randomly generated element of the UUID is added as a protection against any unforseeable problem. Because the network address identifies a unique computer, and the timestamp is unique for each UUID generated from a particular host, those two components should sufficiently ensure uniqueness. A guaranteed UUID contains a reference to the network address of the host that generated the UUID, a timestamp (a record of the precise time of a transaction), and a randomly generated component. The UUID relies upon a combination of components to ensure uniqueness. Depending on the specific mechanisms used, a UUID is either guaranteed to be different or is, at least, extremely likely to be different from any other UUID generated until 3400 A.D. In addition, the UUID can be generated within the application server layer rather than the database, negating the need for extra round-trips to query the value of sequences or automatically assigned primary key values.Ī UUID is a 128-bit number used to uniquely identify an object or entity on the Internet. The use of a Universal Unique Identifier (UUID) solves this problem as each number is unique, rather than the next value in a sequential list of numbers. ![]() The use of sequences can cause a problem during data migrations and replication processes where duplication of the sequences occur. Oracle sequences are frequently used to provide unique numbers for primary keys where an appropriate unique key is not available. In this example the table product is changed by using the ALTER TABLEclause and the clause ADD CONSTRAINT with the name of the UNIQUE constraint (in our example: UQ_product_name_producer) followed by the UNIQUE keyword with the list of columns (in our example there are two columns: name and producer) in parentheses.Home » Articles » 9i » Here Universal Unique Identifier (UUID) Here’s how: Solution 3: Adding a multi-column UNIQUE constraint to an existing tableĪDD CONSTRAINT UQ_product_name_producer UNIQUE(name, producer) You can also make a multiple-column UNIQUE constraint. This is followed by the UNIQUE keyword with column/columns (in our example it is column: name) in parentheses. First we write ALTER TABLE, then we list the name of the table (in our example: product), and next we add the clause ADD CONSTRAINT with the name of the UNIQUE constraint (in our example: UQ_product_name). This is possible by using the ALTER TABLE clause. We want to modify this table and add a UNIQUE constraint to column name. In this example the table product already exists. Solution 2: Adding a UNIQUE constraint to an existing tableĪDD CONSTRAINT UQ_product_name UNIQUE(name) This new table (in our example: product) will contain the column (in our example: name) that stores unique values in rows. In this example a given column (the column name) was made unique by adding the clause UNIQUE at the end of the column definition ( name VARCHAR(100) UNIQUE). ![]() Solution 1: Creating new table with a UNIQUE constraint ![]() The query below presents one way to do it. We would like to make the column name unique in the table product. You would like to make a column unique in a given table in a database.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |