Oracle中的SYS_NC00$ SYS_C000$ SYS_STU SYS_STS 和虚拟字段

SYS_NC00是一种系统自动生成的辅助列，在Oracle 12c以后大量出现在用户表中，其主要伴随一下这些功能出现：

• row archival;
• create index t_i on t(upper(v)); 函数索引
• alter table xxx add (b integer default 1);  default 值

property:

0x0008 = virtual column(old)

0x0020 = hidden column(old)

0x00010000 = expression column(new)

default$: is overloaded to store index expression

name: is system generated. It is SYS_NC<5 digit intcol#>$

SYS_C000$ 伴随以下功能出现：

各种未指定名字的约束

CONSTRAINT constraint_name
Specify a name for the constraint. If you omit this identifier, then Oracle Database generates a name with the form SYS_Cn. Oracle stores the name and the definition of the integrity constraint in the USER_, ALL_, and DBA_CONSTRAINTS data dictionary views (in the CONSTRAINT_NAME and SEARCH_CONDITION columns, respectively).

The references_clause of the ref_constraint syntax lets you define a foreign key constraint on the REF column. This clause also implicitly restricts the scope of the REF column or attribute to the referenced table. However, whereas a foreign key constraint on a non-REF column references an actual column in the parent table, a foreign key constraint on a REF column references the implicit object identifier column of the parent table.

If you do not specify a constraint name, then Oracle generates a system name for the constraint of the form SYS_Cn.

https://docs.oracle.com/cd/B19306_01/server.102/b14200/clauses002.htm#sthref2891

SYS_STU  SYS_STS伴随多列统计信息出现 ； 其中STU代表用户创建的多列统计信息， STS是SYS_STS are system generated from the DECODE in ALL_STAT_EXTENSIONS

Create column groups for the customers_test table based on the usage information captured during the monitoring window.

For example, run the following query:

SELECT DBMS_STATS.CREATE_EXTENDED_STATS(user, ‘customers_test’) FROM DUAL;
Sample output appears below:

###########################################################################
EXTENSIONS FOR SH.CUSTOMERS_TEST
…………………………..
1. (CUST_CITY, CUST_STATE_PROVINCE,
COUNTRY_ID) :SYS_STUMZ$C3AIHLPBROI#SKA58H_N created
2. (CUST_STATE_PROVINCE, COUNTRY_ID):SYS_STU#S#WF25Z#QAHIHE#MOFFMM_ created
###########################################################################
The database created two column groups for customers_test: one column group for the filter predicate and one group for the GROUP BY operation.

用户所自行创建的虚拟列 其SYS.COL$ 的property一般等于65544