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If your dataset is really large and you are looking to partition, you will get more bang for your buck partitioning the table across physical servers.
To enable a unique or primary key constraint, you must have the privileges necessary to create an index on the table.
You need these privileges because Oracle Database creates an index on the columns of the unique or primary key in the schema containing the table.
In addition, the query optimizer is extended so that a seek or scan operation with one condition can be done on (as the logical leading column) and possibly other index key columns, and then a second-level seek, with a different condition, can be done on one or more additional columns, for each distinct value that meets the qualification for the first-level seek operation.
That is, this operation, called a allows the query optimizer to perform a seek or scan operation based on one condition to determine the partitions to be accessed and a second-level index seek operation within that operator to return rows from these partitions that meet a different condition. The partitions are numbered 1 through 4 with the partition boundaries shown by dashed vertical lines.
Using the INDEX option will update index statistics only.