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'}