what is the difference between primary index and primary key?
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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 Key: It is a constraint which imposes limitation on database. ... Unique Index: It is a index which improves the performance while executing queries on your data base. In unique index it also not allows duplicate values in index . ie.no two rows will have the same index key value.
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A primary key is a special constraint on a column or set of columns. ... A table may have only one primary key, but it may be composite (consist of more than one column). A surrogate key is any column or set of columns that can be declared as the primary key instead of a "real" or natural key.
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Primary key does not allow NULL values, but unique key allows NULL values. ... 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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A primary key is a field or set of fields with values that are unique throughout a table. Values of the key can be used to refer to entire records, because each record has a different value for the key. Each table can only have one primary key.
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The PRIMARY KEY constraint uniquely identifies each record in a table. Primary keys must contain UNIQUE values, and cannot contain NULL values. A table can have only ONE primary key; and in the table, this primary key can consist of single or multiple columns (fields).
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A primary key acts as a unique identifier for each record meaning it uniquely identifies each row/record in a table. "A foreign key" is a field in one table that relates the tables together.
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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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Unique key can accept only one null value. By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index. ... Primary key can be made foreign key into another table. In SQL Server, Unique key can be made foreign key into another table.
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No. Primary Key is a unique and non-null key which identify a record uniquely in table. A table can have only one primary key. Candidate key is also a unique key to identify a record uniquely in a table but a table can have multiple candidate keys.
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Primary key emphasizing on uniqueness and avoid duplication value for all records on the same column, while identity provides increasing numbers in a column without inserting data. Both features could be on a single column or on difference one.
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Answer: The primary key is the field or combination of fields that uniquely identifies each record in a table. A foreign key is a field in a related table that is also a primary key in a primary table.
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A surrogate key is a made up value with the sole purpose of uniquely identifying a row. Usually, this is represented by an auto incrementing ID. A primary key is the identifying column or set of columns of a table. Can be surrogate key or any other unique combination of columns (for example a compound key).
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The primary index contains the key fields of the table and a pointer to the non-key fields of the table. The primary index is created automatically when the table is created in the database. ... You can also create further indexes on a table in the ABAP Dictionary. These are called secondary indexes.
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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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Primary Key is a unique and non-null key which identify a record uniquely in table. A table can have only one primary key. Candidate key is also a unique key to identify a record uniquely in a table but a table can have multiple candidate keys.
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In a DB2 table, a Primary Key uniquely identifies the row, no two rows can have the same Primary Key value. (A Primary Key is not required, but you can only have 1). An Index Key can be unique, or not. In an Index Key you can have multiple Rows with the same Index Key Value.