1、写Oracle存储过程时最好不要在其中写Commit语句。一般调用程序会自动Commit数据,比如用NHibernate调用的时候,NHibernate就会自动Commi
1、写Oracle存储过程时最好不要在其中写Commit语句。
一般调用程序会自动Commit数据,,比如用NHibernate调用的时候,NHibernate就会自动Commit数据。如果写了,会造成NHibernate调用完存储过程之后抛出错误。
2、重视Count的特殊比较作用。
在一个Select语句中,用Count对不同的字段进行统计,如果某行数据中被统计字段值为null,不会计入该字段统计值。利用这一点可以进行多表关联统计,比较数据的一致性。
例如:
Select Count(dmc.id) dmcCnt, Count(dmp.id) dmpCnt,
Count(Case dmp.type When 1 Then 1 Else null End) dmp2, Count(dmt.id) dmtCnt
Into i_Count1, i_Count2, i_Count3, i_Count4
From dmc
left join dmp on dmp.id = dmc.dmpid
and dmp.procdoctimestamp = dmc.procdoctimestamp
left join dmt on dmt.dmpid = dmp.id
3、通过关联数据更新一个表时,要注意关联数据的唯一性。
例如:
update (
select dmu.cu, dmu.lmt,
dmcl.cu cu1, dmcl.lmt lmt1
from dmu, dmcl, dmp
where dmu.id = dmp.dmuid
and dmcl.dmpid = dmproc.id
and dmcl.id = dmu.dmclid
)
Set cu = cu1,
lmt = lmt1;
此语句中的dmu表中必须要有dmcl表的主关键字段才可以唯一确定cu1和lmt1的值,否则Oracle会认为你使用多条数据更新一条数据,那样是不允许的。有一些朋友使用一个表的数据更新另一个表的数据失败(ora-01779)常常是这个原因。

MySQL processes data replication through three modes: asynchronous, semi-synchronous and group replication. 1) Asynchronous replication performance is high but data may be lost. 2) Semi-synchronous replication improves data security but increases latency. 3) Group replication supports multi-master replication and failover, suitable for high availability requirements.

The EXPLAIN statement can be used to analyze and improve SQL query performance. 1. Execute the EXPLAIN statement to view the query plan. 2. Analyze the output results, pay attention to access type, index usage and JOIN order. 3. Create or adjust indexes based on the analysis results, optimize JOIN operations, and avoid full table scanning to improve query efficiency.

Using mysqldump for logical backup and MySQLEnterpriseBackup for hot backup are effective ways to back up MySQL databases. 1. Use mysqldump to back up the database: mysqldump-uroot-pmydatabase>mydatabase_backup.sql. 2. Use MySQLEnterpriseBackup for hot backup: mysqlbackup--user=root-password=password--backup-dir=/path/to/backupbackup. When recovering, use the corresponding life

The main reasons for slow MySQL query include missing or improper use of indexes, query complexity, excessive data volume and insufficient hardware resources. Optimization suggestions include: 1. Create appropriate indexes; 2. Optimize query statements; 3. Use table partitioning technology; 4. Appropriately upgrade hardware.

MySQL view is a virtual table based on SQL query results and does not store data. 1) Views simplify complex queries, 2) Enhance data security, and 3) Maintain data consistency. Views are stored queries in databases that can be used like tables, but data is generated dynamically.

MySQLdiffersfromotherSQLdialectsinsyntaxforLIMIT,auto-increment,stringcomparison,subqueries,andperformanceanalysis.1)MySQLusesLIMIT,whileSQLServerusesTOPandOracleusesROWNUM.2)MySQL'sAUTO_INCREMENTcontrastswithPostgreSQL'sSERIALandOracle'ssequenceandt

MySQL partitioning improves performance and simplifies maintenance. 1) Divide large tables into small pieces by specific criteria (such as date ranges), 2) physically divide data into independent files, 3) MySQL can focus on related partitions when querying, 4) Query optimizer can skip unrelated partitions, 5) Choosing the right partition strategy and maintaining it regularly is key.

How to grant and revoke permissions in MySQL? 1. Use the GRANT statement to grant permissions, such as GRANTALLPRIVILEGESONdatabase_name.TO'username'@'host'; 2. Use the REVOKE statement to revoke permissions, such as REVOKEALLPRIVILEGESONdatabase_name.FROM'username'@'host' to ensure timely communication of permission changes.


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