1.建立测试表SQLgt; create table dump (id number,name varchar(20));Table created.SQLgt; insert into dump values (1000,
1.建立测试表
SQL> create table dump (id number,name varchar(20));
Table created.
SQL> insert into dump values (1000,'tomsh');
1 row created.
SQL> insert into dump values (1001,'dumpceshi');
1 row created.
SQL> commit;
Commit complete.
2.查询表在数据文件以及块号
select file_id, block_id from dba_extents
where segment_name = 'DUMP';
SQL> select file_id, block_id from dba_extents
where segment_name = 'DUMP'; 2
FILE_ID BLOCK_ID
---------- ----------
1 85992
SQL> col name format a50;
SQL> select file#, name from v$datafile;
FILE# NAME
---------- --------------------------------------------------
1 /opt/Oracle/db/oradata/oradb/system01.dbf
2 /opt/oracle/db/oradata/oradb/sysaux01.dbf
3 /opt/oracle/db/oradata/oradb/undotbs01.dbf
4 /opt/oracle/db/oradata/oradb/users01.dbf
5 /opt/oracle/db/oradata/oradb/tt.dbf
6 /opt/oracle/db/oradata/tt02.dbf
7 /opt/oracle/db/oradata/oradb/db01.dbf
8 /opt/oracle/db/oradata/qiyi.dbf
8 rows selected.
3.查询表中记录对应的rowid
SQL> select rowid, id, name from dump;
ROWID ID NAME
------------------ ---------- --------------------------------------------------
AAATeFAABAAAU/pAAA 1000 tomsh
AAATeFAABAAAU/pAAB 1001 dumpceshi
SQL>
4.利用dbms_rowid包计算出记录对应的数据块
select dbms_rowid.rowid_block_number('AAATeFAABAAAU/pAAA') from dual;
SQL> select dbms_rowid.rowid_block_number('AAATeFAABAAAU/pAAA') from dual;
DBMS_ROWID.ROWID_BLOCK_NUMBER('AAATEFAABAAAU/PAAA')
---------------------------------------------------
85993
select dbms_rowid.ROWID_OBJECT('AAATeFAABAAAU/pAAA') from dual;
SQL> select dbms_rowid.ROWID_RELATIVE_FNO('AAATeFAABAAAU/pAAA') from dual;
DBMS_ROWID.ROWID_RELATIVE_FNO('AAATEFAABAAAU/PAAA')
---------------------------------------------------
1
5.dump数据文件号为1中的第85993数据块
SQL> alter system dump datafile 1 block 85993;
System altered.
6.跟踪文件内容如下:
*** TRACE FILE RECREATED AFTER BEING REMOVED ***
Start dump data blocks tsn: 0 file#:1 minblk 85993 maxblk 85993
Block dump from cache:
Dump of buffer cache at level 4 for tsn=0, rdba=4280297
BH (0x213f1e48) file#: 1 rdba: 0x00414fe9 (1/85993) class: 1 ba: 0x21268000
set: 3 pool 3 bsz: 8192 bsi: 0 sflg: 1 pwc: 0,25
dbwrid: 0 obj: 79749 objn: 79749 tsn: 0 afn: 1 hint: f
hash: [0x2d2d8e60,0x2d2d8e60] lru: [0x223f450c,0x217f209c]
lru-flags: hot_buffer
ckptq: [NULL] fileq: [NULL] objq: [0x213f67ec,0x2a9ff328]
st: XCURRENT md: NULL tch: 0
flags: block_written_once redo_since_read
LRBA: [0x0.0.0] LSCN: [0x0.0] HSCN: [0xffff.ffffffff] HSUB: [1]
cr pin refcnt: 0 sh pin refcnt: 0
Block dump from disk:
buffer tsn: 0 rdba: 0x00414fe9 (1/85993)
scn: 0x0000.002b4c95 seq: 0x01 flg: 0x06 tail: 0x4c950601
frmt: 0x02 chkval: 0xe3f7 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
Dump of memory from 0xB7116A00 to 0xB7118A00
B7116A00 0000A206 00414FE9 002B4C95 06010000 [.....OA..L+.....]
B7116A10 0000E3F7 000E0001 00013785 002B4C56 [.........7..VL+.]
B7116A20 1FE80000 00031F02 00000000 00160001 [................]
B7116A30 00000892 00C00B43 000E0287 00002002 [....C........ ..]

mysql'sblobissuitableForStoringBinaryDataWithInareLationalDatabase,而ilenosqloptionslikemongodb,redis和calablesolutionsolutionsolutionsoluntionsoluntionsolundortionsolunsonstructureddata.blobobobissimplobisslowdeperformberbutslowderformandperformancewithlararengedata;

toaddauserinmysql,使用:createUser'username'@'host'Indessify'password'; there'showtodoitsecurely:1)choosethehostcarecarefullytocon trolaccess.2)setResourcelimitswithoptionslikemax_queries_per_hour.3)usestrong,iniquepasswords.4)Enforcessl/tlsconnectionswith

toAvoidCommonMistakeswithStringDatatatPesInMysQl,CloseStringTypenuances,chosethirtightType,andManageEngencodingAndCollationsEttingSefectery.1)usecharforfixed lengengtrings,varchar forvariable-varchar forbariaible length,andtext/blobforlargerdataa.2 seterters seterters seterters

mysqloffersechar,varchar,text,and denumforstringdata.usecharforfixed Lengttrings,varcharerforvariable長度,文本forlarger文本,andenumforenforcingDataAntegrityWithaEtofValues。

優化MySQLBLOB請求可以通過以下策略:1.減少BLOB查詢頻率,使用獨立請求或延遲加載;2.選擇合適的BLOB類型(如TINYBLOB);3.將BLOB數據分離到單獨表中;4.在應用層壓縮BLOB數據;5.對BLOB元數據建立索引。這些方法結合實際應用中的監控、緩存和數據分片,可以有效提升性能。

掌握添加MySQL用戶的方法對於數據庫管理員和開發者至關重要,因為它確保數據庫的安全性和訪問控制。 1)使用CREATEUSER命令創建新用戶,2)通過GRANT命令分配權限,3)使用FLUSHPRIVILEGES確保權限生效,4)定期審計和清理用戶賬戶以維護性能和安全。

chosecharforfixed-lengthdata,varcharforvariable-lengthdata,andtextforlargetextfield.1)chariseffity forconsistent-lengthdatalikecodes.2)varcharsuitsvariable-lengthdatalikenames,ballancingflexibilitibility andperformance.3)

在MySQL中處理字符串數據類型和索引的最佳實踐包括:1)選擇合適的字符串類型,如CHAR用於固定長度,VARCHAR用於可變長度,TEXT用於大文本;2)謹慎索引,避免過度索引,針對常用查詢創建索引;3)使用前綴索引和全文索引優化長字符串搜索;4)定期監控和優化索引,保持索引小巧高效。通過這些方法,可以在讀取和寫入性能之間取得平衡,提升數據庫效率。


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