1. PL/SQL performance enhancement : Similar to defining a procedure in an anonymous block, a function can now be defined in SQL through the WITH statement, which can improve the performance of SQL calls.
2. Improve Defaults: include sequence as default value; auto-increment column; specify default value when NULL is explicitly inserted; METADATA-ONLY default value refers to the default value specified when adding a new column, the difference from 11g is that 11g The default value of requires NOT NULL columns.
3. Relax the length restrictions of various data types : increase the length of VARCHAR2, NVARCHAR2 and RAW types to 32K, require compatibility to be set to 12.0.0.0 or higher, and set the initialization parameter MAX_SQL_STRING_SIZE to EXTENDED, this function does not support CLUSTER tables and indexes Organizing tables; this last feature doesn't really change the limits of VARCHAR2, but is implemented through CLOB of OUT OF LINE.
4. TOP N statement implementation : Use "FETCH next N rows" or "OFFSET" in the SELECT statement to specify the top N records or the top percent of records.
5. Line pattern matching: Similar to the function of analysis function, it can perform matching judgment and calculation between lines. The new pattern matching statement in SQL is "match_recognize".
6. Partition improvement : Oracle Database 12c has made many adjustments to the partition function. Oracle ACE Director Yang Tingkun spent a lot of space to interpret the partition improvement, which is divided into 6 parts:
INTERVAL-REFERENCE partition: Combine the interval partition of 11g with the reference partition, so that after the main table automatically adds a partition, all sub-tables, grand-child tables, great-grandchild tables, heavy-duty... grandchild tables can automatically follow the external columns. As new data is added, new partitions are automatically created.
TRUNCATE and EXCHANGE partitions and sub-partitions. Whether it is a TRUNCATE or EXCHANGE partition, executed on the main table, it can be cascaded to run on the sub-table, grand-child table, great-grandchild table, heavy-duty... grandchild table at the same time.
For TRUNCATE, the TRUNCATE operation of all tables is in the same transaction. If it fails in the middle, it will be rolled back to the state header before the command is executed. These two functions are implemented with the keyword CASCADE.
Online partition movement: Online partition movement is realized through the MOVE ONLINE keyword. During the move, queries, DML statements, and partition creation and maintenance operations can be performed on the table and the moved partitions. The entire moving process is transparent to the application. This feature greatly improves overall availability and shortens partition maintenance windows.
Simultaneous operation of multiple partitions: Maintenance operations can be performed on multiple partitions at the same time, such as merging 12 partitions in a year into a new partition, such as SPLITing one partition into multiple partitions. Each partition of the operation can be specified by the FOR statement, and for the RANGE partition, the range of processing partitions can also be specified by TO. Simultaneous operations on multiple partitions are automatically completed in parallel.
Asynchronous global index maintenance: UPDATE GLOBAL INDEX is no longer a pain for very large partitioned tables. Oracle can realize the asynchronous maintenance function of asynchronous global index, even if it is a global index of hundreds of millions of records, after a partition maintenance operation, such as DROP or TRUNCATE, it is still in the VALID state, and the index will not be invalid.
However, the state of the index contains OBSOLETE data, and when the maintenance operation is completed, the index state is restored.
Partial local and global indexes: Oracle's indexes can be defined at the partition level. Either global index or local index can be established on some partitions of a partitioned table, and there are no indexes on other partitions. When accessing full table data through index columns, Oracle implements UNION ALL, partly through index scan, and partly through full partition scan. This can reduce the amount of indexing of historical data, greatly increasing flexibility.
7. Adaptive execution plan : An execution plan with a learning function. Oracle will read the returned results during the actual operation as the input for further execution plan judgment. Therefore, if the statistical information is inaccurate or the real query results and the calculation results are not on time, you can get Better execution plans.
8. Statistics enhancement: The 11th layer of dynamic statistics collection is added, which makes the function of dynamic statistics collection stronger; mixed statistics are added to support the situation that contains a large number of different values, and the data of individual values is skewed; data loading is added Ability for procedures to collect statistics; added session-private statistics for temporary tables.
9. Temporary UNDO: Separate the UNDO of the temporary segment and put it in the TEMP tablespace. The advantages include: reducing the number of UNDOs; reducing the number of REDOs; allowing DML operations on temporary tables on ACTIVE DATA GUARD.
10. Data optimization: Added ILM (Data Lifecycle Management) function, added "Database heat map", directly see the utilization of data in the view, and find out which data is the most "hot" data. Online data compression and data grading can be automatically realized, in which data grading can transfer data files within a defined time to archive storage online, or transfer data tables to archive files regularly. Online data compression can also be achieved.
11. Application Continuity : Before Oracle Database 12c, RAC's FAILOVER only achieved SESSION and SELECT levels, and was powerless for DML operations. When it is set to SESSION, half of the DML is automatically rolled back; and for SELECT, although FAILOVER can not interrupt the query , but for the DML problem even more, it is necessary to roll back manually. In Oracle Database 12c, Oracle finally supports FAILOVER of transactions.
12. Oracle Pluggable Database: The Oracle PDB architecture consists of a container database (CDB) and multiple assembled databases (PDB). The PDB contains independent system tablespaces and SYSAUX tablespaces, etc., but all PDBs share the control files of CDBs , log files, and UNDO tablespaces.