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：
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解决方法:
1.首先创建一个clob的临时字段：
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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。
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alter table table_name rename column content to content_bak; |
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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：
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create or replace function getclob( |
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table_name in varchar2, |
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field_id in varchar2, |
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field_name in varchar2, |
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v_id in number, |
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v_pos in number) return varchar2 |
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is |
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lobloc clob; |
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buffer varchar2(32767); |
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amount number := 2000; |
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offset number := 1; |
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query_str varchar2(1000); |
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begin |
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query_str :='select '||field_name||' from '||table_name||' where '||field_id||'= :id '; |
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--initialize buffer with data to be found |
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EXECUTE IMMEDIATE query_str INTO lobloc USING v_id; |
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offset:=offset+(v_pos-1)*2000; |
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--read 2000 varchar2 from the buffer |
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dbms_lob.read(lobloc,amount,offset,buffer); |
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return buffer; |
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exception |
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when no_data_found then |
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return buffer; |
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end; |
调用存储过程的PHP方法：
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function edt_disp_getclob($id, $field_id, $field_name, $len) { |
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$a = 2000; |
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$b = $a / 2; |
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if (($len % $b) == 0) { |
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$maxpage = floor ( $len / $a ); |
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} else { |
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$maxpage = floor ( $len / $a ) + 1; |
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} |
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$i = 0; |
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$con = ""; |
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$a = new DB_Sql (); |
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while ( $i < $maxpage ) { |
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$i = $i + 1; |
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$sql = "select getclob('table_name','$field_id','$field_name','$id','$i') as h from dual"; |
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//echo $sql." |
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$a->query ( $sql ); |
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if ($a->next_record ()) { |
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$h = $a->Record ["h"]; |
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} |
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$con = $con . $h; |
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} |
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if (! empty ( $con )) { |
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$a->disconnect (); |
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} |
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return $con; |
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} |
调用：
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$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 IN VARCHAR2,
clob_column_name IN VARCHAR2,
primary_Key_Column_names IN VARCHAR2,
primary_key_values IN VARCHAR2,
offset_i IN NUMBER,
read_length_i IN NUMBER,
RES OUT VARCHAR2,
total_length OUT 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------------------
*/
tmpPrimaryKeys VARCHAR2 (2000); --To save primary_Key_Column_names temporarily(暂存主键,主键是以'}'分隔的字符串)
tmpPrimaryKeyValues VARCHAR2 (2000); --To save primary_key_values temporarily(暂存主键键值,以'}'分隔的字符串)
i NUMBER; --循环控制变量
tmpReadLength NUMBER; --暂存要读取的长度
sqlStr VARCHAR2 (6000); --Query string(查询字符串)
sqlCon VARCHAR2 (5000); --Query condition(查询条件)
TYPE tmparray IS TABLE OF VARCHAR2 (5000) INDEX BY BINARY_INTEGER;
arrayPrimaryKeys tmparray; --To save the analyse result of primary_Key_Column_names (暂存分析后得到的主键名)
arrayPrimaryKeyValues tmparray; --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
clobvar CLOB := 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;