CUBRID学习笔记 26 数据类型3

接上面的集合

集合之 set

每个集合元素是不同的值, 但是类型只能是一种.也可以有其他表的记录 如下

CREATE TABLE set_tbl ( col_1 set(CHAR(1)));

INSERT INTO set_tbl VALUES ({‘c‘,‘c‘,‘c‘,‘b‘,‘b‘,‘a‘});

INSERT INTO set_tbl VALUES ({NULL});

INSERT INTO set_tbl VALUES ({‘‘});

SELECT * FROM set_tbl;

col_1

======================

{‘a‘, ‘b‘, ‘c‘}

{NULL}

{‘ ‘}

SELECT CAST(col_1 AS MULTISET), CAST(col_1 AS LIST) FROM set_tbl;

cast(col_1 as multiset)   cast(col_1 as sequence)

============================================

{‘a‘, ‘b‘, ‘c‘}  {‘a‘, ‘b‘, ‘c‘}

{NULL}  {NULL}

{‘ ‘}  {‘ ‘}

INSERT INTO set_tbl VALUES (‘‘);

ERROR: Cannot coerce ‘‘ to type set.

集合 MULTISET

和set差不多.但是元素的内容可重复

CREATE TABLE multiset_tbl ( col_1 multiset(CHAR(1)));

INSERT INTO multiset_tbl VALUES ({‘c‘,‘c‘,‘c‘,‘b‘,‘b‘, ‘a‘});

SELECT * FROM multiset_tbl;

col_1

======================

{‘a‘, ‘b‘, ‘b‘, ‘c‘, ‘c‘, ‘c‘}

SELECT CAST(col_1 AS SET), CAST(col_1 AS LIST) FROM multiset_tbl;

cast(col_1 as set)   cast(col_1 as sequence)

============================================

{‘a‘, ‘b‘, ‘c‘}  {‘c‘, ‘c‘, ‘c‘, ‘b‘, ‘b‘, ‘a‘}

集合 之list

可重复的,但是是有序的.保持插入前的顺序.list本身不会对内容排序.

CREATE TABLE list_tbl ( col_1 list(CHAR(1)));

INSERT INTO list_tbl VALUES ({‘c‘,‘c‘,‘c‘,‘b‘,‘b‘, ‘a‘});

SELECT * FROM list_tbl;

col_1

======================

{‘c‘, ‘c‘, ‘c‘, ‘b‘, ‘b‘, ‘a‘}

SELECT CAST(col_1 AS SET), CAST(col_1 AS MULTISET) FROM list_tbl;

cast(col_1 as set)  cast(col_1 as multiset)

============================================

{‘a‘, ‘b‘, ‘c‘}  {‘a‘, ‘b‘, ‘b‘, ‘c‘, ‘c‘, ‘c‘}

隐式转换

Implicit Type Conversion Table 2

转换规则

插入和修改

数据会转为目标列的数据类型

CREATE TABLE t(i INT);

INSERT INTO t VALUES(‘123‘);

SELECT * FROM t;

i

=============

123

函数

参数被转为函数的参数类型,如下  mod参数需要的是数字类型. 所以传入的字符串被转为数字

SELECT MOD(‘123‘,‘2‘);

mod(‘123‘, ‘2‘)

==========================

1.000000000000000e+00

层次关系

• Date/Time Type (DATETIME > TIMESTAMP > DATE > TIME)
• Approximate Numeric Type (MONETARY > DOUBLE > FLOAT)
• Exact Numeric Type (NUMERIC > BIGINT > INT > SHORT)
• String Type (CHAR/NCHAR > VARCHAR/VARNCHAR)

比较操作

字段类型的转换

If operand2 is a set operator(IS IN, IS NOT IN, = ALL, = ANY, < ALL, < ANY, <= ALL, <= ANY, >= ALL, >= ANY), the exception above is not applied.

如果operand2 是集合操作 如 IS IN, IS NOT IN, = ALL, = ANY, < ALL, < ANY, <= ALL, <= ANY, >= ALL, >= ANY, 则不适用

数字和字符串比较

字符串将被转换为dobule类型

CREATE TABLE t(i INT, s STRING);

INSERT INTO t VALUES(1,‘1‘),(2,‘2‘),(3,‘3‘),(4,‘4‘), (12,‘12‘);

SELECT i FROM t WHERE i < ‘11.3‘;

i

=============

1

2

3

4

SELECT (‘2‘ <= 11);

(‘2‘<11)

=============

1

字符串和日期比较

字符串被转为日期

SELECT (‘2010-01-01‘ < date‘2010-02-02‘);

(‘2010-01-01‘<date ‘2010-02-02‘)

==================================

1

SELECT (date‘2010-02-02‘ >= ‘2010-01-01‘);

字符串类型和系统的数字类型

数字被转为字符串

PREPARE s FROM ‘SELECT s FROM t WHERE s < ?‘;

EXECUTE s USING 11;

s

===================

‘1‘

字符串类型和数字类型

数字被转为字符串

SELECT s FROM t WHERE s > 11;

s

==================

‘2‘

‘3‘

‘4‘

‘12‘

SELECT s FROM t WHERE s BETWEEN 11 AND 33;

s

======================

‘2‘

‘3‘

‘12‘

字符串和日期类型

日期转为字符串

SELECT s FROM t;

s

======================

‘01/01/1998‘

‘01/01/1999‘

‘01/01/2000‘

SELECT s FROM t WHERE s <= date‘02/02/1998‘;

s

======================

‘01/01/1998‘

‘01/01/1999‘

‘01/01/2000‘

(date ‘2010-02-02‘>=‘2010-01-01‘)

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