ORA-30344: number of child cols different from number of parent level cols
Cause: The number of child columns specified in a JOIN KEY clause is not the same as the number of columns in the specified parent level.
Action: Check the child columns and the columns in the definition of the referenced parent level and correct the discrepency.
ORA-30344 错误指出，使用二级分区表结构定义时，子表级别要求与父表级别列数不一致。
ORA-30344: number of child cols different from number of parent level cols
被定义的子表的级别的列数必须与父表的级别的列数完全一致。
例子：
父表定义：
CREATE TABLE PARENT_TABLE (
ID NUMBER,
CUSTOMER_ID NUMBER,
SEQ NUMBER
);
子表：
CREATE TABLE CHILD_TABLE (
ID NUMBER,
CUSTOMER_ID NUMBER
);
在这种情况下，查询：
ALTER TABLE CHILD_TABLE
partition by range (CUSTOMER_ID)
subpartition by list (SEQ)
(PARTITION P1 VALUES LESS THAN (10)
(SUBPARTITION P1S1 VALUES (1), P1S2 VALUES (2)));
就会产生ORA-30344:number of child cols different from number of parent level cols 错误。这是因为子表没有定义SEQ列，而父表却定义了该列。
1.确保子表的列数与父表的级别的列数完全一致。
2.如果必须使用部分不同的列，则可以将记录放入null空间，以使子表与父表列数一致：
ALTER TABLE CHILD_TABLE
partition by range (CUSTOMER_ID)
subpartition by list (SEQ)
(PARTITION P1 VALUES LESS THAN (10)
(SUBPARTITION P1S1 VALUES (1, NULL), P1S2 VALUES (2, NULL) );