oracle如何操作clob数据类型

Posted 2023-03-04

在存储过程里面，需要有个变量存储一段字符串，因为这段字符串可能很长，可能达到几万个字符，所以考虑用clob来存储，但是我在存储过程中如下写，报错message:=empty_clob();
DBMS_LOB.WRITEAPPEND(message, 10, '0123456789');说指定的lob定位符无效，谁知道如何往clob里面直接写入字符串，在线等。

在做数据库开发的时候，有时候会遇到需要读取Oracle数据库中的clob类型的数据的情况。本着代码复用的目的，写了下面的存储过程：读取数据库中clob字段的数据。

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; 参考技术A clob 类型的操作很容易的，可以当成 varchar2 一样处理。blob处理上才困难一些。