Firebird/InterBase内置函数使用说明

Firebird/InterBase内置函数使用说明(转自：圣域天堂)

2008-10-12 20:56

加*号为FB2.0加入的函数

整理:剑雷(jianlei) 2006-10-13

1. COUNT, AVG, MAX, MIN, SUM

说明:通用统计函数,不详细介绍了

2. EXTRACT(timestamp_part FROM value)

说明:EXTRACT(YEAR/MONTHE/DAY/WEEKDAY FROM 字段名)

从日期型字段中分离出年,月,日及一个星期的第几天

3. CAST(value AS datatype)

说明:转换数据类型

4. LOWER() *

说明:返回小写值

5. UPPER()

说明:返回大写值

6. TRIM() *

说明:去除字符串两边的空格

7. SUBSTRING(string FROM pos FOR length)

说明:取字符串子串,注意,第一个字符的位置是1

8. BIT_LENGTH *

说明:返回字符串位(bit)数

9. CHAR_LENGTH/CHARACTER_LENGTH *

说明:返回字符串字符数

10. OCTET_LENGTH *

说明:返回字符串字节数

11. CASE

说明:通过执行外来的一组条件取得相应的返回值

举例

i) 简单

SELECT o.ID, o.Description,

CASE o.Status

WHEN 1 THEN 'confirmed'

WHEN 2 THEN 'in production'

WHEN 3 THEN 'ready'

WHEN 4 THEN 'shipped'

ELSE 'unknown status ''' || o.Status || ''''

END

FROM Orders o;

ii) 表达式

SELECT o.ID, o.Description,

CASE

WHEN (o.Status IS NULL) THEN 'new'

WHEN (o.Status = 1) THEN 'confirmed'

WHEN (o.Status = 3) THEN 'in production'

WHEN (o.Status = 4) THEN 'ready'

WHEN (o.Status = 5) THEN 'shipped'

ELSE 'unknown status ''' || o.Status || ''''

END

FROM Orders o;

12. IIF (<search_condition>, <value1>, <value2>)

说明:表达式为真,返回value1否则返回value2

等价于以下语句:

CASE

WHEN <search_condition> THEN <value1>

ELSE <value2>

END

13. NULLIF(V1,V2)

说明:如果V1=V2,返回NULL,否则返回V1

等价于以下语句:

CASE WHEN V1 = V2 THEN NULL ELSE V1 END

举例

UPDATE PRODUCTS

SET STOCK = NULLIF(STOCK,0)

14. COALESCE(V1, V2, …, Vn)

说明:如果V1为Null,返回V2,否则返回V1,

如果 n >= 3, 等于如下case语句:

CASE

WHEN V1 IS NOT NULL THEN V1

ELSE COALESCE (V2,...,Vn)

END

举例

SELECT

PROJ_NAME AS Projectname,

COALESCE(e.FULL_NAME,'[< not assigned >]') AS Employeename

FROM

PROJECT p

LEFT JOIN EMPLOYEE e

ON (e.EMP_NO = p.TEAM_LEADER);

SELECT

COALESCE(Phone,MobilePhone,'Unknown') AS "Phonenumber"

FROM Relations;

15.获当前日期：

select current_date from rdb$database

获当前时间：

select current_time from rdb$database

16.Firebird数据库的取值范围

在其它SQL数据库里，有一个 Top n的子句，可以取头n条记录，Firebird不支持这个子句，但是它有更强大的子句：FIREST n SKIP n。

FIRST n表示提取头n条记录,SKIP n 表示从第几条开始提取，比如，我要从学生表里取语文成绩名次在11至15名的学生名单，SQL语句如下：

select first 5 skip 10 SNAME,YUWEN from achieve order by YUWEN desc

一、分页写法小例：

SELECT FIRST 10 templateid,code,name FROM template ;

SELECT FIRST 10 SKIP 10 templateid,code,name FROM template ;

SELECT * FROM shop ROWS 1 TO 10; --firebird2.0支持这种写法

二、显示表名和表结构

SHOW TABLES;

SHOW TABLE tablename;

三、使用ISQL连接数据库

firebird%92bin>isql -u sysdba -p masterkey

SQL>CONNECT 'E:companyxmwsoftnewxmwsoftc2dbcts2.fdb';

或

SQL>CONNECT 'E:%92'

CON>USER 'sysdba'

CONT>PASSWORD 'masterkey';

四、更新字段注释

UPDATE RDB$RELATION_FIELDS

SET RDB$DESCRIPTION = '描述信息'

WHERE (RDB$RELATION_NAME = 'SHOP')

AND (RDB$FIELD_NAME = 'CREDIT_BUY')

五、显示字段注释

SELECT RDB$FIELD_NAME,RDB$DESCRIPTION

FROM RDB$RELATION_FIELDS

WHERE (RDB$RELATION_NAME = 'SHOP')

AND (DB$FIELD_NAME = 'CREDIT_BUY')

六、更新表注释

UPDATE RDB$RELATIONS

SET RDB$DESCRIPTION = '描述信息'

WHERE RDB$RELATION_NAME = 'TABLE_NAME';

七、查询所有的表和视图（包括系统表和系统视图）

SELECT RDB$RELATION_NAME

FROM RDB$RELATIONS;

八、查询所有的用户表和用户视图

SELECT RDB$RELATION_NAME

FROM RDB$RELATIONS

WHERE RDB$SYSTEM_FLAG = 0;

九、查询所有的用户表

SELECT RDB$RELATION_NAME

FROM RDB$RELATIONS

WHERE RDB$SYSTEM_FLAG = 0

AND RDB$VIEW_BLR IS NULL;

十、查所有用户表、用户视图所有字段及相关定义

SELECT

a.RDB$RELATION_NAME,

b.RDB$FIELD_NAME,

b.RDB$FIELD_ID,

d.RDB$TYPE_NAME,

c.RDB$FIELD_LENGTH,

c.RDB$FIELD_SCALE

FROM RDB$RELATIONS a

INNER JOIN RDB$RELATION_FIELDS b

ON a.RDB$RELATION_NAME = b.RDB$RELATION_NAME

INNER JOIN RDB$FIELDS c

ON b.RDB$FIELD_SOURCE = c.RDB$FIELD_NAME

INNER JOIN RDB$TYPES d

ON c.RDB$FIELD_TYPE = d.RDB$TYPE

WHERE a.RDB$SYSTEM_FLAG = 0

AND d.RDB$FIELD_NAME = 'RDB$FIELD_TYPE'

ORDER BY a.RDB$RELATION_NAME, b.RDB$FIELD_ID;

十一、查找某表的所有字段及相关定义

SELECT

A.RDB$FIELD_NAME,

B.RDB$FIELD_TYPE,

B.RDB$FIELD_LENGTH,

B.RDB$FIELD_PRECISION,

B.RDB$FIELD_SCALE

FROM RDB$RELATION_FIELDS A, RDB$FIELDS B

WHERE A.RDB$RELATION_NAME = 'tablename'

AND A.RDB$FIELD_SOURCE = B.RDB$FIELD_NAME

ORDER BY A.RDB$FIELD_POSITION;

十二、查找某表的主键定义字段

SELECT A.RDB$FIELD_NAME

FROM RDB$INDEX_SEGMENTS A, RDB$RELATION_CONSTRAINTS B

WHERE B.RDB$CONSTRAINT_TYPE = 'PRIMARY KEY'

AND B.RDB$RELATION_NAME = 'tablename'

AND A.RDB$INDEX_NAME = B.RDB$INDEX_NAME

ORDER BY A.RDB$FIELD_POSITION;

十三、查找某表的外键定义

SELECT

r1.RDB$CONSTRAINT_NAME,

rind.RDB$FIELD_NAME,

r2.RDB$RELATION_NAME

FROM

RDB$RELATION_CONSTRAINTS r1,

RDB$RELATION_CONSTRAINTS r2,

RDB$REF_CONSTRAINTS ref,

RDB$INDEX_SEGMENTS rind

WHERE r1.RDB$RELATION_NAME = 'tablename'

AND r1.RDB$CONSTRAINT_TYPE = 'FOREIGN KEY'

AND r1.RDB$CONSTRAINT_NAME = ref.RDB$CONSTRAINT_NAME

AND ref.RDB$CONST_NAME_UQ = r2.RDB$CONSTRAINT_NAME

AND r1.RDB$INDEX_NAME = rind.RDB$INDEX_NAME;