Database Administrator

1. to get a new bug, we must first reproduce the problem. this is necessary for the code issue, and it is almost necessary for the customer's data issue. if it is a code problem, you cannot modify the code without recreating it. If it is changed,

Today is. If you encounter a lib problem today, record it again. This is a case and a process of solving the problem. When we use sqlplus to log on to a unix database, problems such as: xxxxxx bad ELF interpreter: No such file or directory may occur.

A decision tree is used to classify data for prediction. This decision tree method first forms a decision tree based on the training set data. If the tree cannot correctly classify all objects, select some exceptions and add them to the training set

Schema is the logical structure and feature description of all data in the database, also known as the conceptual mode or conceptual view. A view can be understood as a set of record values that the user or programmer sees and uses in the

1. Create a directory SQL> create directory dump_file as '/db/backup '; 2. Grant Directory Permissions SQL> grant read, write on directorydump_file to bam; View directory SQL> select * from dba_directories; 3. Backup SQL> expdp user/pwd directory =

1. index creation Syntax:Create uniuqe | bitmap index . ON . (| ASC | DESC, | ASC | DESC ,...)TABLESPACE STORAGE LOGGING | NOLOGGINGCOMPUTE STATISTICSNOCOMPRESS | COMPRESS NOSORT | REVERSEPARTITION | global partition Description1) UNIQUE | BITMAP:

When I was using the database today, I suddenly found that SQL Server08 could not be connected. Problem: So I searched for this problem on the Internet and found many similar questions. Since this problem was not encountered by a few people, it

Differences between variable reference methods # {} and $ {} in MyBatis er File By default, MyBatis uses the # {} syntax to generate a PreparedStatement statement and set the PreparedStatement parameter safely. In this process, MyBatis performs

In the morning, we performed data migration. After deploying slave2, we found that the logs of the three machines were rampant: Old slave: 2014-05-29 14:35:35 996 [Note] Slave: received end packet from server, apparent master shutdown: 2014-05-29 14

PostgreSQL supports hstore to store data such as KEY-> VALUE, which is also similar to ARRAY or JSON. To use this type of data efficiently, you must use efficient indexes. Let's take a look at the performance of two different types of indexes for

Various MySQL indexes (because most of them do not deliberately distinguish between search engines) INDEX (Common INDEX): the most basic INDEX with no restrictions Alter table 'table _ name' add index index_name ('column ') UNIQUE (UNIQUE index):

Description provided by SQL SERVER.Bit: an integer of 0 or 1Int: an integer from-2 ^ 31 (-2,147,483,648) to 2 ^ 31 (2,147,483,647)Smallint: integer number from-2 ^ 15 (-32,768) to 2 ^ 15 (32,767)Tinyint: integer number from 0 to 255Decimal: number

I had nothing to do this morning. I suddenly wanted to write views and temporary tables as follows: View: View definition: A table exported from one or more tables (or views. The view and table are different: the view is a virtual table, that is,

Nowadays, more and more projects are using report tools. However, there are many report tools on the Chinese market, which are mixed. In the face of so many products, it is difficult to distinguish between advantages and disadvantages from one

Once the installation is complete, the MySQL server should be started automatically. Sudo start mysql # start it manually Sudo stop mysql # manually stop After you modify the configuration file, you need to restart mysqld to make these changes take

During the interview, you will be asked a variety of strange questions. You may be able to give the most perfect solution from the actual point of view when thinking about the solution. The following is a database-related interview question:

There is a ticket for the expansion process based on the CRM system. In the database, tc_worksheettc_worksheet_1_1 tc_worksheet_attr tc_worksheet_mattr tc_worksheet_xattr. The ticket data is stored in the preceding tables at the same time.  

When oracle Plsql executes update or delete, It is stuck when Plsql is stuck or when code executes SQL. When this problem occurs during development, I copied the SQL statement and executed it in plsql. The SQL spelling is correct, but the plsql

Today is very strange, import a single table to report the error of ORA-01401, also searched a circle online, and my situation is different. This error occurs because the characters stored in the exported dmp file are different in bytes. My database

Serial number Task Command combination 1 Delete 0-byte files Find.-type f-size 0-exec rm-rf {}\;Find. type f-size 0-delete 2 View processes in a descending order of memory Ps-e-o "% C: % p: % z: % a" |