what is the difference between unique index and unique constraint in oracle?
447328
Unique index is for performance. Though unique constraints and unique indexes both help with uniqueness, their objectives differ. A unique constraint is meant to enforce data integrity. A unique constraint might create a unique index implicitly, but it does not rely on or need the index to maintain data integrity.
770580
An index is a schema object that contains an entry for each value that appears in the indexed column(s) of the table or cluster and provides direct, fast access to rows. Oracle Database supports several types of index: Normal indexes.
682
Difference between Primary Key and Foreign Key. Primary key uniquely identify a record in the table. Foreign key is a field in the table that is primary key in another table. ... By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index.
179730
A unique index is just an index with a unique constraint, nothing more, nothing less. A clustered index orders the data phsyically on the disk to match the index. It is useful if you access the data in the table very often via just one column, e.g. via the primary key.
1217550
- PK: primary key (column is part of a pk) - NN: not null (column is nullable) - UQ: unique (column is part of a unique key) - AI: auto increment (the column is auto incremented when rows are inserted) [additional data type flags, depend on used data type]
1168438
asifkabirdba wrote: unique index - when we have define a column as a primary key/unique constraint then an index will be created automatically for that column. ... index - create index on the columns using "create index command" to retrieve the rows faster.
619981
Difference between Primary Key and Foreign Key. Primary key uniquely identify a record in the table. Foreign key is a field in the table that is primary key in another table. Primary Key can't accept null values.
1402370
['Values are atomic.', 'All of the values in a column have the same data type.', 'Each row is unique.', 'The sequence of columns is insignificant.', 'The sequence of rows is insignificant.', 'Each column has a unique name.', 'Integrity constraints maintain data consistency across multiple tables.']
1142699
Unique and non-unique indexes. Unique indexes are indexes that help maintain data integrity by ensuring that no two rows of data in a table have identical key values. ... When a unique index is defined for a table, uniqueness is enforced whenever keys are added or changed within the index.
71836
The main difference between Unique and Distinct in SQL is that Unique helps to ensure that all the values in a column are different while Distinct helps to remove all the duplicate records when retrieving the records from a table. ... Unique and Distinct are two of them which allows writing SQL queries.
1243222
The names of database objects need not be unique in a database. However, column names and index names must be unique within a table, and other object names must be unique for each owner within a database.
982515
a unique constraint bound to a single column, refer to @Column). Entity is object-oriented and table is relation-oriented. You can only use the entity name in the HQL (Hibernate Query Language) to query objects, and the table name in the native SQL.
33342
A primary key is a unique field on a table but it is special in the sense that the table considers that row as its key. This means that other tables can use this field to create foreign key relationships to themselves. A unique constraint simply means that a particular field must be unique. Primary keys can't be null.
961810
A query can use an indexed view in its execution plan even if it does not satisfy these GROUP BY restrictions. If the view definition contains a GROUP BY clause, the key of the unique clustered index can reference only the columns specified in the GROUP BY clause.
1180091
Column-level constraints refer to a single column in the table and do not specify a column name (except check constraints). They refer to the column that they follow. Table-level constraints refer to one or more columns in the table. Table-level constraints specify the names of the columns to which they apply.
941090
Unique was the old syntax while Distinct is the new syntax,which is now the Standard sql. Unique creates a constraint that all values to be inserted must be different from the others. Distinct results in the removal of the duplicate rows while retrieving data.
643130
A primary key uniquely identifies a record in the relational database table, whereas a foreign key refers to the field in a table which is the primary key of another table.