Oracle - DBMS_LOB函数和用法

GETLENGTH

    返回指定 LOB 数据的长度的函数

DBMS_LOB.GETLENGTH(lob_loc  IN  BLOB/CLOB/BFILE/NCLOB) RETURN  INTEGER;

OPEN

    打开LOB对象    

DBMS_LOB.OPEN(
lob_loc    IN  OUT  NOCOPY  BLOB/CLOB/BFILE,
open_mode  IN  BINARY_INTEGER    -- 只读:DBMS_LOB.LOB_READONLY；读写：DBMS_LOB.LOB_READWRITE
);

READ

    从 LOB 数据中读取指定长度数据到缓冲区(变量中)的过程

DBMS_LOB.READ(
lob_loc  IN  BLOB/CLOB/BFILE,     -- LOB 数据
amount   IN  OUT  NOCOPY  BINARY_INTEGER),    -- IN:要读取的字符数；OUT：实际读取的字符数
offset   IN  INTEGER,      --  起始位置
buffer   OUT  RAW/VARCHAR2    -— 存储返回数据的变量
);

    例：

DECLARE

var_clob    CLOB;
var_buff    VARCHAR2(1000);
var_len     NUMBER(4);
var_start   NUMBER(4);

BEGIN

SELECT RESUME INTO var_clob FROM TLOB WHERE NO = 1;
var_len := DBMS_LOB.GETLENGTH(varc);
var_start := 1;
DBMS_LOB.READ(var_clob, var_len, var_start, var_buff);
DBMS_OUTPUT.PUT_LINE('RETURN: '||var_buff);

END;

WRITE

    将指定数量的数据写入LOB的过程。

DBMS_LOB.WRITE(
lob_loc  IN  OUT  NOCOPY  BLOB/CLOB,   -- 被写入 LOB
amount   IN  BINARY_INTEGER,   -- 写入长度(指写入 LOB 数据)
offset   IN  INTEGER,          -- 写入起始位置(指被写入 LOB)
buffer   IN  RAW/VARCHAR2      -- 写入 LOB 的数据
);

    例：

DECLARE

v_clob    CLOB;
v_wstr    VARCHAR2(1000);
v_strat   NUMBER(4);
v_len     NUMBER(4);

BEGIN

v_wstr := 'CLOB';
v_len := LENGTH(VWSTR);
v_strat := 5;

SELECT RESUME INTO v_clob FROM TLOB WHERE NO = 1 FOR UPDATE;  --更新 LOB 数据需要 FOR UPDATE 锁定

DBMS_LOB.WRITE(v_clob, v_len, v_strat, v_wstr);
DBMS_OUTPUT.PUT_LINE('改写结果为: ' || v_clob);

COMMIT;

END;

APPEND

    将指定的LOB数据追加到指定的LOB数据后的过程。

DBMS_LOB.APPEND(
dest_lob  IN  OUT  NOCOPY  BLOB,       --追加到的目标LOB
src_lob   IN  BLOB                     -- 用来追加的LOB
);

    例：

DECLARE

varcl    CLOB;
vastr    VARCHAR2(1000);

BEGIN

vastr := '，这是大对象列';
SELECT RESUME INTO varcl FROM TLOB WHERE NO = 1 FOR UPDATE;
DBMS_LOB.APPEND(varcl, vastr);
COMMIT;
DBMS_OUTPUT.PUT_LINE('追加结果为: ' || varcl);

END;

WRITEAPPEND  

    将缓冲区数据写到LOB尾部  

DBMS_LOB.WRITEAPPEND(
lob_loc  IN  OUT  NOCOPY  BLOB/CLOB/NCLOB,
amount   IN  BINARY_INTEGER,
buffer   IN  RAW/VARCHAR2
);

TRIM

    截断LOB数据中从第一位置开始指定长度的部分数据的过程

DBMS_LOB.TRIM(
lob_loc  IN  OUT  NOCOPY  BLOB/CLOB/NCLOB,   --LOB数据
newlen   IN  INTEGER  -- 阶段长度
);

    例：

DECLARE

varc  CLOB;
len   NUMBER(4);

BEGIN

len := 4;
SELECT RESUME INTO varc FROM TLOB WHERE NO = 1 FOR UPDATE;
DBMS_LOB.TRIM(varc, len);
COMMIT;
DBMS_OUTPUT.PUT_LINE('截断结果为: '||varc);

END;

CLOSE

    关闭已经打开的LOB

DBMS_LOB.CLOSE(lob_loc  IN  OUT  NOCOPY  BLOB/CLOB/BFILE);

 
SUBSTR

    从LOB数据中提取子字符串的函数。

DBMS_LOB.SUBSTR(
lob_loc  IN  BLOB/CLOB/BFILE,   -- 提取的来源
amount   IN  INTEGER:=32762,   -- 提取长度
offset   IN  INTEGER:=1   -- 开始位置
)RETURN  RAW/VARCHAR2;   -- 提取到的内容

    例：

DECLARE

vclob   CLOB;
sustr   VARCHAR2(1000);
len     NUMBER(4);
start   NUMBER(4);

BEGIN

SELECT RESUME INTO vclob FROM TLOB WHERE NO = 1;
len := 4;
start := 1;
sustr := DBMS_LOB.SUBSTR(vclob, len, start);
DBMS_OUTPUT.PUT_LINE('结果为: '||sustr);

END;

   
INSTR

    从LOB数据中查找子字符串位置的函数。

DBMS_LOB.INSTR(
lob_loc  IN  BLOB/CLOB/NCLOB/BFILE,
pattern  IN  RAW/VARCHAR2,
offset   IN  INTERGER:=1,
nth      IN  INTEGER:=1
)RETURN  INTEGER;

    例：

DECLARE

vclob    CLOB;
instr    VARCHAR2(1000);
sustr    VARCHAR2(1000);
len      NUMBER(4);

BEGIN

SELECT RESUME INTO vclob FROM TLOB WHERE NO = 1;
sustr := '大对象';
len := DBMS_LOB.INSTR(vclob, instr);
DBMS_OUTPUT.PUT_LINE('位置为: ' || len);

sustr := DBMS_LOB.SUBSTR(vclob, LENGTH(instr), len);
DBMS_OUTPUT.PUT_LINE('位置为' || len || '长度为' || LENGTH(instr) || '的子字符串为：' || sustr);

END;

COMPARE

    比较二个大对象是否相等。返回数值0为相等，-1为不相等。

DBMS_LOB.COMPARE(
lob_1       IN  BLOB/CLOB/BFILE,
lob_2       IN  BLOB/CLOB/BFILE,
amount      IN  INTEGER:=4294967295,      --要比较的字符数(CLOB),字节数(BLOB)
offset_1    IN  INTEGER:=1,               --lob_1 的起始位置
offset_2    IN  INTEGER:=1                --lob_2 的起始位置
);

    例：

DECLARE

varc1    CLOB;
varc2    CLOB;
varc3    CLOB;
len      NUMBER(4);

BEGIN

SELECT RESUME INTO varc1 FROM TLOB WHERE NO = 1;
SELECT RESUME INTO varc2 FROM TLOB WHERE NO = 2;
SELECT RESUME INTO varc3 FROM TLOB WHERE NO = 3;

len := DBMS_LOB.COMPARE(varc1,varc1);
DBMS_OUTPUT.PUT_LINE('比较的结果为: ' || len);

len := DBMS_LOB.COMPARE(varc2,varc3);
DBMS_OUTPUT.PUT_LINE('比较的结果为: ' || len);

END;

 
ERASE

     删除LOB数据中指定位置的部分数据的过程

DBMS_LOB.ERASE(
lob_loc  IN  OUT  NOCOPY  BLOB/CLOB/NCLOB,
amount   IN  OUT  NOCOPY  INTEGER,        --字符/字节数
offset   IN  INTEGER:=1                   —起始位置
);

     例：

DECLARE

vclob       CLOB;
len         NUMBER(4);
start       NUMBER(4);

BEGIN

len := 1;
start := 5;
SELECT RESUME INTO vclob FROM TLOB WHERE NO = 1 FOR UPDATE;
DBMS_LOB.ERASE(vclob, len, start);
COMMIT;
DBMS_OUTPUT.PUT_LINE('擦除结果为: '|| clob);

END;

COPY

    从指定位置开始将源LOB复制到目标LOB

DBMS_LOB.COPY(
dest_lob     IN  OUT  NOCOPY  BLOB/CLOB/NCLOB,  -- 目标的LOB
src_lob      IN  BLOB/CLOB/NCOB,    -- 拷贝的来源的LOB
amount       IN  INTEGER,           -- 拷贝的长度
dest_offset  IN  INTEGER:=1,        -- 目标从哪里开始接收
src_offset   IN  INTEGER:=1         -- 来源从来历开始拷贝
);

    例：

DECLARE

vdest_lob    CLOB;
vsrc_lob     CLOB;
amount       NUMBER;
dest_offset  NUMBER;
src_offset   NUMBER;

BEGIN

SELECT RESUME INTO vdest_lob FROM TLOB WHERE NO = 1 FOR UPDATE;
SELECT RESUME INTO vsrc_lob FROM TLOB WHERE NO = 2 ;

amount := DBMS_LOB.GETLENGTH(vsrc_lob);
dest_offset := DBMS_LOB.GETLENGTH(vdest_lob) + 1;
src_offset := 1;

DBMS_LOB.COPY(vdest_lob, vsrc_lob, amount, dest_offset, src_offset);
DBMS_OUTPUT.PUT_LINE('拷贝结果为: ' || vdest_lob);

END;

CREATETEMPORARY

    在用户的临时表空间中，建立临时LOB

DBMS_LOB.CREATETEMPORARY(
lob_loc  IN  OUT  NOCOPY  BLOB/DLOB/NCLOB,
cache    IN  BOOLEAN,     -- 是否将LOB读取到缓冲区
dur      IN  PLS_INTEGER:=10    -- 指定何时清除临时LOB（10：会话结束时；12：调用结束时）
);

ISTEMPORARY

    确定定位符是否为临时LOB

DBMS_LOB.ISTEMPORARY(lob_loc  IN  BLOB/CLOB/NCLOB)  RETURN  INTEGER;

FILEEXISTS

    确定FILE_LOC对应的OS文件是否存在。1：存在；0：不存在

DBMS_LOB.FILEEXISTS(file_loc  IN  BFILE) RETURN  INTEGER;

FILEGETNAME

    获取BFILE定位符所对应的目录别名和文件名

DBMS_LOB.FILEGETNAME(
file_loc    IN  BFILE,
dir_alias   OUT  VARCHAR2,
filename    OUT  VARCHAR2
);

FILEISOPEN

    确定BFILE对应的OS文件是否打开     

DBMS_LOB.FILEISOPEN(file_loc  IN  BFILE)  RETURN  INTEGER;

FREETEMPORARY

    释放在默认临时表空间中的临时LOB

DBMS_LOB.FREETEMPORARY(lob_loc  IN  OUT  NOCOPY  BLOB/CLOB/NCLOB);

FILEOPEN

    打开文件

DBMS_LOB.FILEOPEN(
file_loc   IN  OUT  NOCOPY  BFILE,
open_mode  IN  BINARY_INTEGER:FILE_READONLY
);

LOADBLOBFROMFILE

    将BFILE数据装载到BLOB中，并且在装载后取得最新的偏移位置

DBMS_LOB.LOADBLOBFROMFILE(
dest_loc     IN  OUT  NOCOPY  BLOB,
src_bfile    IN  BFILE,
amount       IN  INTEGER,
dest_offset  IN  OUT  INTEGER,
src_offset   IN  OUT  INTEGER
);

    例：

DECLARE

piece_bfile BFILE := BFILENAME('BFILE_DATA','test.jpg'); --创建一个BFILE指针
photo_blob BLOB;

BEGIN

SELECT bifle_content INTO photo_blob FROM bfile_demo WHERE bfile_id = 101;

DBMS_LOB.OPEN(photo_blob, DBMS_LOB.LOB_READWRITE);
DBMS_LOB.OPEN(piece_bfile);

DBMS_LOB.LOADBLOBFROMFILE(photo_blob, piece_bfile, DBMS_LOB.LOBMAXSIZE, 1, 1);

DBMS_LOB.CLOSE(photo_blob);
DBMS_LOB.CLOSE(piece_bfile);

END;

FILECLOSE

    关闭打开的BFILE定位符所指向的OS文件

DBMS_LOB.FILECLOSE(FILE_LOC  IN  OUT  NOCOPY  BFILE);

FILECLOSEALL

    关闭当前会话已经打开的所有BFILE文件

DBMS_LOB.FILECLOSEALL();

参考

    http://blog.csdn.net/cunxiyuan108/article/details/16873733

    http://www.linuxidc.com/Linux/2011-12/49911.htm

    http://www.th7.cn/db/Oracle/201406/58454.shtml