📅  最后修改于: 2023-12-03 15:17:24.916000             🧑  作者: Mango
LOB(Large Object)是指大型的二进制数据对象,比如图片、音频、视频等。在数据库中保存LOB时,需要使用LOB定位符和LOB值。
LOB定位符和LOB值是一个重要的数据结构,它们可以让程序员方便地处理和操作LOB数据。
以下是使用Oracle PL/SQL和MySQL SQL语言处理LOB定位符和LOB值的示例代码:
DECLARE
v_lob_locator BLOB;
v_lob BFILE;
BEGIN
-- 打开LOB值
v_lob := BFILENAME('<directory name>', '<file name>');
DBMS_LOB.fileopen(v_lob);
-- 插入LOB值,获取LOB定位符
INSERT INTO <table name>(<LOB column name>)
VALUES(EMPTY_BLOB())
RETURNING <LOB column name>
INTO v_lob_locator;
-- 将LOB值写入到LOB列中
DBMS_LOB.loadfromfile(v_lob_locator, v_lob, DBMS_LOB.getlength(v_lob));
DBMS_LOB.fileclose(v_lob);
COMMIT;
END;
/
DECLARE
v_lob_locator BLOB;
v_lob BFILE;
BEGIN
-- 打开LOB值
v_lob := BFILENAME('<directory name>', '<file name>');
DBMS_LOB.fileopen(v_lob);
-- 获取LOB定位符
SELECT <LOB column name> INTO v_lob_locator
FROM <table name>
WHERE <PK column name> = <PK value>
FOR UPDATE;
-- 将LOB值写入到LOB列中
DBMS_LOB.filetruncate(v_lob_locator, 0);
DBMS_LOB.loadfromfile(v_lob_locator, v_lob, DBMS_LOB.getlength(v_lob));
DBMS_LOB.fileclose(v_lob);
COMMIT;
END;
/
DECLARE
v_lob_locator BLOB;
v_lob CLOB;
BEGIN
-- 获取LOB定位符
SELECT <LOB column name> INTO v_lob_locator
FROM <table name>
WHERE <PK column name> = <PK value>;
-- 读取LOB值
DBMS_LOB.createtemporary(v_lob, TRUE);
DBMS_LOB.copy(v_lob, v_lob_locator, DBMS_LOB.getlength(v_lob_locator));
DBMS_OUTPUT.put_line(v_lob);
DBMS_LOB.freetemporary(v_lob);
END;
/
INSERT INTO <table name>(<LOB column name>)
VALUES(LOAD_FILE('<file path>'));
UPDATE <table name>
SET <LOB column name> = LOAD_FILE('<file path>')
WHERE <PK column name> = <PK value>;
SELECT <LOB column name>
FROM <table name>
WHERE <PK column name> = <PK value>;