oracle delete table partition

In Oracle database management, in order to improve query efficiency, we often use partitioning technology to divide large tables according to certain rules. However, partitioning also has its drawbacks. When we do not need certain partitions, we need to delete them from the table. At this time, we need to use Oracle's method of deleting table partitions.

There are many ways to delete table partitions in Oracle. Choosing the appropriate method according to different scenarios can improve the deletion efficiency. This article will introduce three common methods for Oracle to delete table partitions.

Method 1: Delete partition

This method directly deletes a partition of the table, which is the simplest and most direct method. The syntax is as follows:

ALTER TABLE table_name DROP PARTITION partition_name;

Among them, table_name is the table name, and partition_name is the name of the partition that needs to be deleted.

Example:

ALTER TABLE orders DROP PARTITION p2001;

This command will delete the partition named p2001 in the table named orders.

It should be noted that when using this command to delete a single partition, if the deleted partition contains data, the data will also be deleted at the same time. In addition, when partitioning a large table, since the size of each partition is limited, if the table is too large and the number of partitions is large, you need to wait patiently for the Drop Partition statement to be executed, otherwise time may be wasted.

Method 2: Merge Partitions

If we want to delete multiple partitions in the table, and the data between these partitions can be merged, we can use the method of merging partitions. For example, if we want to delete all order information from 2001 to 2005, and this order information happens to be stored in different partitions of the same table, we can merge the partitions from 2001 to 2005 and delete them as one partition. .

The syntax is as follows:

ALTER TABLE table_name MERGE PARTITIONS partition1[,partition2, ...] INTO new_partition;

Among them, table_name is the table name, partition1, partition2, etc. are the partition names that need to be merged, and new_partition is the new partition name.

Example:

ALTER TABLE orders MERGE PARTITIONS p2001, p2002,p2003,p2004,p2005 INTO p01_05;

This command will merge the partitions p2001, p2002, p2003, p2004, and p2005 with the table name orders into one partition p01_05. After merging, we can use the Drop Partition command introduced in Method 1 to delete the p01_05 partition.

It should be noted that we need to make our own judgment as to whether the data between each partition can be merged.

Method 3: Turn the partitioned table into a non-partitioned table

If we want to delete a large number of partitions and the method of merging partitions is not applicable, then we can turn the partitioned table into a non-partitioned table. Partition table, and then delete unnecessary data to achieve the purpose of deleting partitions.

The syntax is as follows:

ALTER TABLE table_name SET SUBPARTITION TEMPLATE (SUBPARTITION subpartition_name VALUES(value_list)) 
    DROP SUBPARTITION template_name DROP UNUSED PARTITIONS;

Among them, table_name is the table name, subpartition_name is the subpartition name, value_list is the value range of this subpartition, and template_name is the template name. Using the above statement will insert the table table_name subpartition subpartition_name into the template template_name, thereby deleting this subpartition. If there are other sub-partitions in the table, use DROP UNUSED PARTITIONS to directly delete these unused sub-partitions.

Example:

ALTER TABLE orders SET SUBPARTITION TEMPLATE(SUBPARTITION p2001 VALUES(200101,200102,200103,200104)) DROP SUBPARTITION p2001 DROP UNUSED PARTITIONS;

This command will delete the subpartitions of partition p2001 whose table name is orders, and whose value range is 200101, 200102, 200103, and 200104.

It should be noted that when executing this method, the partitioned table will be converted into a normal table, so if you still need to use partitioning technology later, you need to re-establish the partitioned table.

Summary

Using partitioning technology can provide us with better database performance, but during the partitioning process, if some partitions are no longer needed and need to be deleted, we can use Oracle to delete them at this time Table partitioning operations are completed. The above describes three commonly used methods for deleting partitions. They need to be selected appropriately according to the scenario and needs to avoid invalid execution and waste time, and at the same time, it can also improve the efficiency of partition deletion.

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