instr和substr存儲(chǔ)過(guò)程，分析內(nèi)部大對(duì)象的內(nèi)容
instr函數(shù)
instr函數(shù)用于從指定的位置開(kāi)始，從大型對(duì)象中查找第N個(gè)與模式匹配的字符串。
用于查找內(nèi)部大對(duì)象中的字符串的instr函數(shù)語(yǔ)法如下：
dbms_lob.instr( lob_loc in blob, pattern in raw, offset in integer := 1; nth in integer := 1) return integer; dbms_lob.instr( lob_loc in clob character set any_cs, pattern in varchar2 character set lob_loc%charset, offset in integer:=1, nth in integer := 1) return integer;
lob_loc為內(nèi)部大對(duì)象的定位器
pattern是要匹配的模式
offset是要搜索匹配文件的開(kāi)始位置
nth是要進(jìn)行的第N次匹配
substr函數(shù)
substr函數(shù)用于從大對(duì)象中抽取指定數(shù)碼的字節(jié)。當(dāng)我們只需要大對(duì)象的一部分時(shí)，通常使用這個(gè)函數(shù)。
操作內(nèi)部大對(duì)象的substr函數(shù)語(yǔ)法如下：
dbms_lob.substr( lob_loc in blob, amount in integer := 32767, offset in integer := 1) return raw; dbms_lob.substr( lob_loc in clob character set any_cs, amount in integer := 32767, offset in integer := 1) return varchar2 character set lob_loc%charset;
其中各個(gè)參數(shù)的含義如下：
lob_loc是substr函數(shù)要操作的大型對(duì)象定位器
amount是要從大型對(duì)象中抽取的字節(jié)數(shù)
offset是指從大型對(duì)象的什么位置開(kāi)始抽取數(shù)據(jù)。
如果從大型對(duì)象中抽取數(shù)據(jù)成功，則這個(gè)函數(shù)返回一個(gè) raw 值。如果有一下情況，則返回null：
1 任何輸入?yún)?shù)尾null
2 amount 1
3 amount > 32767
4 offset 1
5 offset > LOBMAXSIZE
示例如下：
declare
source_lob clob;
pattern varchar2(6) := 'Oracle';
start_location integer := 1;
nth_occurrence integer := 1;
position integer;
buffer varchar2(100);
begin
select clob_locator into source_lob from mylobs where lob_index = 4;
position := dbms_lob.instr(source_lob, pattern, start_location, nth_occurrence);
dbms_output.put_line('The first occurrence starts at position:' || position);
nth_occurrence := 2;
select clob_locator into source_lob from mylobs where lob_index = 4;
position := dbms_lob.instr(source_lob, pattern, start_location, nth_occurrence);
dbms_output.put_line('The first occurrence starts at position:' || position);
select clob_locator into source_lob from mylobs where lob_index = 5;
buffer := dbms_lob.substr(source_lob, 9, start_location);
dbms_output.put_line('The substring extracted is: ' || buffer);
end;
/
The first occurrence starts at position:8
The first occurrence starts at position:24
The substring extracted is: Oracle 9i
PL/SQL 過(guò)程已成功完成。
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