what is difference between index and primary key in sap?
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Primary Key: that is used for uniquely identified a perticular row of a database table . Primary INDEX: That is used for getting a index from a database table and that indexing is done on unique based.
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Unique Constraint. A constraint has different meaning to an index. It gives the optimiser more information and allows you to have foreign keys on the column, whereas a unique index doesn't.
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['The primary key for a row is unique; it does not match the primary key of any other row in the table.', 'The primary key is not null, no component of the primary key may be set to null.']
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A key is a set of columns or expressions on which we build an index. While an index is a structure that is stored in database, keys are strictly a logical concept. Index help us in fast accessing a record, whereas keys just identify the records uniquely.
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A Non-Unique Primary Index (NUPI) means that the values for the selected column can be non-unique. Duplicate values can exist. A Non-Unique Primary Index will almost never spread the table rows evenly. An All-AMP operation will take longer if the data is unevenly distributed.
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Difference between Super Key and Primary Key: Super Key is an attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation. Primary Key is a minimal set of attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation.
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A primary key uniquely identifies each record within a table and relates records to additional data stored in other tables. A natural key might require several fields to accomplish a unique identity for each record.
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Yes, primary key is automatically indexed in MySQL because primary key, index, etc gets stored into B-trees. All engines including InnoDB as well as MyISAM automatically supports the primary key to be indexed. The primary key is implicitly indexed in InnoDB, MyISAM, and other engines.
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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.
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Key Differences Between Primary key and Unique key: Primary key will not accept NULL values whereas Unique key can accept one NULL value. ... A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index.
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You can only have 1 primary key in a database table. ... You can have more than 1 unique key table column (unlike primary key which means only 1 table column in the table is unique). INDEX also creates uniqueness. MySQL (example) will create a indexing table for the column that is indexed.
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Primary key is used to identify data uniquely therefore two rows can't have the same primary key. It can't be null. On the other hand, foreign key is used to maintain relationship between two tables. Primary of a table act as forgein key in the other table.
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A primary key is a column or a set of columns that uniquely identify a row in a table. A primary key should be short, stable and simple. A foreign key is a field (or collection of fields) in a table whose value is required to match the value of the primary key for a second table. ... A table can have multiple foreign keys.
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Choosing a primary key is one of the most important steps in good database design. A primary key is a table column that serves a special purpose. Each database table needs a primary key because it ensures row-level accessibility.
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Primary Key is a column that is used to uniquely identify each tuple of the table. It is used to add integrity constraints to the table. Only one primary key is allowed to be used in a table. ... Unique key is a constraint that is used to uniquely identify a tuple in a table.
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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.
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In Dense Index, an index entry appears for every search-key whereas for Sparse index, an index entry appears for only some of the search-key values.