Database Administrator

A horizontal table is a common table creation method. For example, a table has the following structure:Primary Key, Field 1, Field 2, Field 3...If it becomes a vertical table, the table structure is:Primary Key, field code, and field value.The field

Mysqladmin MySQL client management tool Flush-hosts Flush all cached hosts (max_connect_errors)Refresh all information in host BufferFlush-logs Flush all logsRefresh all logsFlush-status Clear status variablesClear status variablesFlush-tables Flush

The mysql5.6 subquery is no longer a vase or a decoration. Mysql subqueries have always been known for poor performance. Therefore, the solution is to replace subqueries with table connections. In mysql, subqueries are only considered a function

Analytic functions compute an aggregate value based on a group of rows. they differ from aggregate functions in that they return multiple rows for each group. the group of rows is called a window and is defined by the analytic_clause. for each row,

Today, I tried the latest version of mysql cluster7.2, which has major drawbacks when adding data nodes online. What are the disadvantages? A: First of all, the newly added nodes must restart all NODB data nodes and restart all SQL nodes according

1. First install the following necessary rpm packages with the root user # Rpm-Uvh libaio-0.3.106-3.2.x86_64.rpm# Rpm-Uvh libaio-devel-0.3.106-3.2.x86_64.rpm 2. Supporting asynchronous I/O at the system levelUnlike setting asynchronous IO in RHEL3

1. Use the trace file to restore SQL> alter database backup controlfile to trace; -- back up the control file to the trace file Database altered. SQL> @ gettrace -- get the path of the trace file TRACE_FILE_NAME---------------------------------------

Introduction: Recently, I often see some posts about Oracle GG implementation cases in forums. It is true that GG does not have a lot of comprehensive information in various forums, especially the real implementation cases are even more rare. In

MySQL is a scarce resource for PHP programs. By default, the maximum number of connections for MySQL is 100, that is, a maximum of 100 MySQL clients can be connected. Therefore, PHP has made some optimizations when using MySQL connections. These

ORA-01779 errors may occur when you try to update a subquery in Oracle. The error message is as follows: ORA-01779: cannot modify a column which maps to a non-key-preserved table for example, this error occurs when you use the following update

When executing the following command, you must first enter db2cmd in the running of the client to initialize or su to the db2 instance. I. Common sense commands 1. db2 connect to -- connect to the local database name Db2 connect to user using --

Because the company needs to add computers to the domain, the computer name is modified. In addition, Oracle is rarely used at ordinary times, and services are started manually. In the afternoon, Oracle was suddenly used for a test. It was found

In Oracle, after delete is used to delete data, the storage capacity of the database is not reduced, and after a table is deleted using delete, the query speed of this table is the same as before deletion, it will not change. Because oralce has an

Today, the customer reported that the query was slow. Because the query was in a production environment, the test was not allowed. Therefore, refer to the following blog to export the statistics to the test server for SQL statement optimization. 1.

Part 1: Test conditions A. IP Address 192.168.1.52 node1 192.168.1.53 node2 192.168.1.55node1-vip 192.168.1.56 node2-vip 10.10.10.52 node1-priv 10.10.10.53 node2-priv 192.168.1.60 racdb-cluster-scan B. Version: Oracle 11gR2 (11.2.0.2) Part 2: Test

UNDOThe tablespace is restored when there is hot standby and no transaction occurs. First, let's take a look at ensuringUndoNo transactions in the tablespace SQL> select XID USN, XIDSLOT, XIDSQN fromv $ transaction; No rows selected Second, confirm

The following error occurs when an extract is started today: 22:41:02 ERROR OGG-00446 Oracle GoldenGate Capture for Oracle, e1_rks2. prm: cocould not find archived log for sequence 10770 thread 1 under default destinations SQL , error retrieving

1. First, you must understand that the dmp file imported and exported from Oracle is executed using the cmd command, rather than SQL plus. You can also use PLSQLDev to import and export data. Note that the executable file export selects the

Rollup is an extension of group by, which performs subtotal and total operations. cube contains rollup, which is a more granular subtotal and total. When there is only one field, rollup and cube are the same. You can use grouping to test rollup and

View existing VG # Lsvg Rootvg Oravg Datavg   View the usage status of each VG # Lsvg oravg Focus on several values Pp size: 512 megabyte (s) Note: SIZE of each PP FREE PPs: 147 (75264 megabytes) Note: number of available pp and Space # Lsvg