CUBRID数据类型之集合类型SET,MULTISET,LIST or SEQUENCE

作者：黄军敬

1.下面先以对比方式介绍一下三种集合类型特征（其中LIST和SEQUENCE指的是同一种类型，只是名称不同）

TYPE	DESCRIPTION	DEFINITION	INPUT DATA	STORED DATA
SET	不允许重复 数据先按照定义的类型顺序 再按照从小到大的顺序存储	col_name SET VARCHAR(20)	{'c','c','c','b','b', 'a'}	{'a','b','c'}
col_name SET (int,VARCHAR(20))	{3,3,3,2,2,1,0,'c','c','c','b','b', 'a'} {3,3,2,'d',2,1,0,'c','c', 3,5,'b','b','a'}	{0,1,2,3,'a','b','c'} {0, 1, 2, 3, 5, 'a', 'b', 'c', 'd'}
MULTISET	允许重复 数据先按照定义的类型顺序 再按照从小到大的顺序存储	col_name MULTISET VARCHAR(20)	{'c','c','c','b','b', 'a'}	{'a','b','b','c','c','c'}
col_name MULTISET (int, VARCHAR(20))	{3,3,3,2,2,1,0,'c','c','c','b','b', 'a'} {3,3,2,'d',2,1,0,'c','c', 3,5,'b','b','a'}	{0,1,2,2,3,3,3,'a','b','b', 'c','c','c'} {0, 1, 2, 2, 3, 3, 3, 5, 'a', 'b', 'b', 'c', 'c', 'd'}
LIST SEQUENCE	允许重复 数据按输入顺序存储	col_name LIST VARCHAR(20)	{'c','c','c','b','b', 'a'}	{'c','c','c','b','b','a'}
col_name LIST (int, VARCHAR(20))	{3,3,3,2,2,1,0,'c','c','c','b','b', 'a'} {3,3,2,'d',2,1,0,'c','c', 3,5,'b','b','a'}	{3,3,3,2,2,1,0,'c','c','c','b','b', 'a'} {3, 3, 2, 'd', 2, 1, 0, 'c', 'c', 3, 5, 'b', 'b', 'a'}

集合类型数据具有如下特点
1) 以一对大括号”{}”作为起始标志，元素与元素之间用逗号”,”分割.
2) 集合内部支持多种数据类型，例如set(int, char(1),date)
3) 集合内部也支持用户自定义类型，如以已存在的表作为数据类型
例如
Create table t1 (t int)
Create table t2 (t set t1)

2. 集合类型之间是支持类型转换的，具体参考下表

	TO
FROM		SET	MULTISET	LIST
SET	-	O	O
MULTISET	O	-	O
LIST	O	O	-

3 举例
1) SET

csql> CREATE TABLE set_tbl ( col_1 set(int, CHAR(1))); csql> INSERT INTO set_tbl VALUES ({3,3,3,2,2,1,0,'c','c','c','b','b','a'}); csql> INSERT INTO set_tbl VALUES ({NULL}); csql> INSERT INTO set_tbl VALUES ({''}); csql> SELECT * FROM set_tbl; csql> ;xr === <Result of SELECT Command in Line 1> === col_1 ====================== {0, 1, 2, 3, 'a', 'b', 'c'} {NULL} {' '} csql> SELECT CAST(col_1 AS MULTISET), CAST(col_1 AS LIST) FROM set_tbl; csql> ;xr === <Result of SELECT Command in Line 1> === cast(col_1 as multiset) cast(col_1 as sequence) ============================================ {0, 1, 2, 3, 'a', 'b', 'c'} {0, 1, 2, 3, 'a', 'b', 'c'} {NULL} {NULL} {' '} {' '} csql> INSERT INTO set_tbl VALUES (''); ERROR: Cannot coerce '' to type set. ERROR: Incompatible data type on attribute col_1.

2) MULTISET

csql> CREATE TABLE multiset_tbl ( col_1 multiset(int, CHAR(1))); csql> INSERT INTO multiset_tbl VALUES ({3,3,3,2,2,1,0,'c','c','c','b','b', 'a'}); csql> SELECT * FROM multiset_tbl; csql> ;xr === <Result of SELECT Command> === col_1 ====================== {0, 1, 2, 2, 3, 3, 3, 'a', 'b', 'b', 'c', 'c', 'c'} csql> SELECT CAST(col_1 AS SET), CAST(col_1 AS LIST) FROM multiset_tbl; csql> ;xr === <Result of SELECT Command in Line 1> === cast(col_1 as set) cast(col_1 as sequence) ============================================ {0, 1, 2, 3, 'a', 'b', 'c'} {0, 1, 2, 2, 3, 3, 3, 'a', 'b', 'b', 'c', 'c', 'c'}

3) LIST or SEQUENCE

csql> CREATE TABLE list_tbl ( col_1 list(int, CHAR(1))); csql> INSERT INTO list_tbl VALUES ({3,3,3,2,2,1,0,'c','c','c','b','b', 'a'}); csql> SELECT * FROM list_tbl; csql> ;xr === <Result of SELECT Command in Line 1> === col_1 ====================== {3, 3, 3, 2, 2, 1, 0, 'c', 'c', 'c', 'b', 'b', 'a'} csql> SELECT CAST(col_1 AS SET), CAST(col_1 AS MULTISET) FROM list_tbl; csql> ;xr === <Result of SELECT Command in Line 1> === cast(col_1 as set) cast(col_1 as multiset) ============================================ {0, 1, 2, 3, 'a', 'b', 'c'} {0, 1, 2, 2, 3, 3, 3, 'a', 'b', 'b', 'c', 'c', 'c'}