oracle中varchar2字段转clob字段，并提供读取方法。

转载自：http://my.oschina.net/guyfar/blog/73837

问题描述

CMS系统中有一个表的字段(如：content)是varchar2类型(最多只能存储4000字符)，不够用了，因此将其改为clob类型(支持4G存储量)。

如果该字段content列不为空的话，不能直接通过sql语句修改其字段类型，会报ORA-22858的错误，如图所示：

解决方法:

1.首先创建一个clob的临时字段：

1	alter table table_name add (tmp clob);

2.然后将content字段内容全部复制到tmp字段中，具体方法请见：

http://my.oschina.net/guyfar/blog/73829

3.修改content字段名为content_bak，将tmp的字段名改为content即可。

1	alter table table_name rename column content to content_bak;

2

3	alter table table_name rename column tmp to content;

到这里就完成了字段类型的转换。

虽然数据类型已经转换完成，会发现调用此字段的程序会报错。那是因为通过sql查询出的clob字段是对象类型，因此会报错。

我是通过存储过程来调用的，存储过程如下：

01	create or replace function getclob(

02

03	table_name in varchar2,

04

05	field_id in varchar2,

06

07	field_name in varchar2,

08

09	v_id in number,

10

11	v_pos in number) return varchar2

12

13

is

14

15	lobloc clob;

16

17	buffer varchar2(32767);

18

19	amount number :=2000;

20

21	offset number :=1;

22

23	query_str varchar2(1000);

24

25

begin

26

27	query_str := 'select ' ||field_name|| ' from ' ||table_name|| ' where ' ||field_id|| '= :id ' ;

28

29	--initialize buffer with data to be found

30

31	EXECUTE IMMEDIATE query_str INTO lobloc USING v_id;

32

33	offset:=offset+(v_pos-1)*2000;

34

35	--read 2000 varchar2 from the buffer

36

37	dbms_lob. read (lobloc,amount,offset,buffer);

38

39	return buffer;

40

41

exception

42

43	when no_data_found then

44

45	return buffer;

46

47

end ;

调用存储过程的PHP方法：

01	function edt_disp_getclob( $id , $field_id , $field_name , $len ) {

02	$a = 2000;

03	$b = $a / 2;

04	if (( $len % $b ) ==0) {

05	$maxpage = floor ( $len / $a );

06

} else {

07	$maxpage = floor ( $len / $a ) + 1;

08

}

09

$i = 0;

10	$con = "" ;

11	$a = new DB_Sql ();

12	while ( $i < $maxpage ) {

13	$i = $i + 1;

14	$sql = "select getclob('table_name','$field_id','$field_name','$id','$i') as h from dual" ;

15	//echo $sql."<BR>";exit;

16	$a ->query ( $sql );

17	if ( $a ->next_record ()) {

18	$h = $a ->Record [ "h" ];

19

}

20	$con = $con . $h ;

21

}

22	if (! empty ( $con )) {

23	$a ->disconnect ();

24

}

25	return $con ;

26

}

调用：

1	$con = edt_disp_getclob( $id , 'id' , 'con' , $con_len );

参数说明：

$id ：要查询的行

id:按ID查询

con ：字段名称

$con_len :要查询的字段长度(提前通过sql查出)

至此，所有改动完成。

CREATE OR REPLACE PROCEDURE prc_read_clob (

table_name INVARCHAR2,

clob_column_name INVARCHAR2,

primary_Key_Column_namesINVARCHAR2,

primary_key_values INVARCHAR2,

offset_i INNUMBER,

read_length_i INNUMBER,

RES OUT VARCHAR2,

total_lengthOUT NUMBER)

AS

/**

Autor:Hanks_gao.

Create Date:2008/12/10

Description:This procedure is to read clob value by conditions

--------------------------------------------------------------

-----------------Parameters descritption----------------------

table_name: The table that contains clob/blob columns(表名)

clob_column_name : Clob/blob column name of table_name(类型为clob的字段名)

primary_key_column_names : The columns seperated by '}' that can fix only one row data (that is primary key) (主键名，以'}'分隔的字符串)

primary_key_values : The primary keyes values that seperated by '}'(主键键值,以'}'分隔的字符串)

offset_i : The offset of reading clob data(要读取的位移量)

read_length_i : The length of reading clob data per times(要读取的长度)

res : Return value that can be referenced by application(读取的结果)

total_length : The total length of readed clob data(数据库查询到的clob数据的总长度)

-----------------End Parameters descritption------------------

*/

tmpPrimaryKeysVARCHAR2 (2000); --To save primary_Key_Column_names temporarily(暂存主键,主键是以'}'分隔的字符串)

tmpPrimaryKeyValuesVARCHAR2 (2000); --To save primary_key_values temporarily(暂存主键键值,以'}'分隔的字符串)

iNUMBER; --循环控制变量

tmpReadLength NUMBER; --暂存要读取的长度

sqlStrVARCHAR2 (6000); --Query string(查询字符串)

sqlConVARCHAR2 (5000); --Query condition(查询条件)

TYPE tmparray IS TABLE OF VARCHAR2 (5000) INDEX BY BINARY_INTEGER;

arrayPrimaryKeystmparray; --To save the analyse result of primary_Key_Column_names (暂存分析后得到的主键名)

arrayPrimaryKeyValuestmparray; --To save the analyse result of primary_key_values(暂存分析后得到的主键键值)

BEGIN

total_length :=0;

RES :='';

DECLARE

clobvarCLOB :=EMPTY_CLOB;

BEGIN

tmpPrimaryKeys :=primary_Key_Column_names;

tmpPrimaryKeyValues :=primary_key_values;

i :=0;

WHILE INSTR (tmpPrimaryKeys,'}') > 0

LOOP --Analyse the column names of primary key(将主键分开,相当于arrayPrimaryKeys =tmpPrimaryKeys.split("}") )

arrayPrimaryKeys (i) :=

SUBSTR (tmpPrimaryKeys,1,(INSTR (tmpPrimaryKeys,'}') - 1));

tmpPrimaryKeys :=

SUBSTR (tmpPrimaryKeys,(INSTR (tmpPrimaryKeys,'}') + 1));

i :=i + 1;

END LOOP;

i :=0;

WHILE INSTR (tmpPrimaryKeyValues,'}') > 0

LOOP--Analyse the values of primary key

arrayPrimaryKeyValues (i) :=

SUBSTR (tmpPrimaryKeyValues,

1,

(INSTR (tmpPrimaryKeyValues,'}') - 1));

tmpPrimaryKeyValues :=

SUBSTR (tmpPrimaryKeyValues,

(INSTR (tmpPrimaryKeyValues,'}') + 1));

i :=i + 1;

END LOOP;

IF arrayPrimaryKeys.COUNT () <> arrayPrimaryKeyValues.COUNT ()

THEN--判断键与键值是否能匹配起来

res :='KEY-VALUE NOT MATCH';

RETURN;

END IF;

i :=0;

sqlCon :='';

WHILE i <arrayPrimaryKeys.COUNT ()

LOOP

sqlCon :=

sqlCon

|| ' AND '

|| arrayPrimaryKeys (i)

|| '='''

|| REPLACE (arrayPrimaryKeyValues (i),'''','''''')

|| '''';

i :=i + 1;

END LOOP;

sqlStr :=

'SELECT '

|| clob_column_name

|| ' FROM '

|| table_name

|| ' WHERE 1=1 '

|| sqlCon

|| ' AND ROWNUM =1';--组查询字符串

DBMS_LOB.createtemporary (clobvar,TRUE);

DBMS_LOB.OPEN (clobvar,DBMS_LOB.lob_readwrite);

EXECUTE IMMEDIATE TRIM (sqlStr) INTO clobvar; --执行查询

IF offset_i <=1

THEN

total_length :=DBMS_LOB.getlength (clobvar);

END IF;

IF read_length_i <=0

THEN

tmpReadLength :=4000;

ELSE

tmpReadLength :=read_length_i;

END IF;

DBMS_LOB.READ (clobvar,

tmpReadLength,

offset_i,

res); --读取数据

IF DBMS_LOB.ISOPEN (clobvar) =1

THEN

DBMS_LOB.CLOSE (clobvar);

END IF;

END;

EXCEPTION

WHEN OTHERS

THEN

res :='';

total_length :=0;

END;