SQL programming-advanced queries and precautions

SQL programming-advanced queries and precautions 1. What is a subquery? When one query is a condition of another query, it is called a subquery. For subquery, you can use several simple commands to Construct Powerful composite commands. Subqueries

MySQL modifies the copied user and password

MySQL modifies the copied user and password In the production environment, you sometimes need to modify the password for copying a MySQL user account, for example, if the password is lost, or because multiple different copy users want to be a single

Use expdp (non-local) to remotely export data

Use expdp (non-local) to remotely export data Background: Some time ago, test data (one table) needs to be imported into the local database from a remote test database. The table has about 5 million data records and more than 160 fields. The exp/imp

MHA online switching process

MHA online switching process In addition to automatic monitoring and switching, MySQL MHA provides online failover, which is mostly used for hardware upgrades and MySQL database migration. This mode provides fast switching and elegant blocking of

MySQL index and Query Optimization

MySQL index and Query Optimization Index type: Common indexes are the most basic index types and have no restrictions such as uniqueness. The unique index is basically the same as the normal index, but all index column values are unique. The primary

MySQL explain analysis Query

MySQL explain analysis Query Brief description: You can use the EXPLAIN or DESC keyword to simulate the optimizer to execute SQL query statements to know how MySQL processes your SQL statements. This helps you analyze the performance bottleneck of

How to diagnose sysdate Return Error time in RAC Environment

How to diagnose sysdate Return Error time in RAC Environment Recently, some rac environments have been used to access sysdate and return the error time. This problem often occurs when the database link is created through Listener, and, in most cases,

Oracle cursor use full solution

Oracle cursor use full solution This document covers almost all aspects of Oracle cursor use, all passed the test -- Declare the CURSOR; CURSOR cursor_name IS select_statement -- For Loop cursor-- (1) define a cursor-- (2) define the cursor

Monitor multiple database loads simultaneously using Shell scripts

Monitor multiple database loads simultaneously using Shell scripts In normal work, there are still a lot of databases to be managed. Because of the relationship between remote access and permissions, some graphic tools cannot be accessed. Sometimes

MySQL Character Set knowledge Summary

MySQL Character Set knowledge Summary Character Set & character encoding Character set is a collection of multiple characters. There are many types of Character sets. Each Character set contains different numbers of characters. The characters here

Oracle query fields by Field Type

Oracle query fields by Field Type Sometimes we need to query specific field information in Oracle through the field name, field type, field length, field comment, table name. For example, my colleague asked me yesterday if blob type is used in our

MySQL database index

MySQL database index Advantages of creating an index in MySQL: 1. Greatly speed up data retrieval; 2. Create a unique index to ensure the uniqueness of each row of data in the database table; 3. Accelerate the connection between tables; 4. When you

Oracle listener cannot be started (TNS-12537, TNS-12560, TNS-00507)

Oracle listener cannot be started (TNS-12537, TNS-12560, TNS-00507) An error is reported when the Oracle listener is started, indicating that the connection is interrupted. [Oracle @ localhost ~] $ Lsnrctl start LSNRCTL for Linux: Version 11.2.0.1.0-

Explore Redis data expiration policies

Explore Redis data expiration policies Use the EXPIRE key seconds command to set the data expiration time. If the return value is 1, the setting is successful. If the return value is 0, the key does not exist or the expiration time cannot be set

Application of Oracle cursor-for, loop, and if

Application of Oracle cursor-for, loop, and if I. Requirements When Will Oracle cursors and the for, loop, and if statements be used? Let's look at this requirement first: There is a student teaching table T_TEACHING. Each student has several

MySQL profiling Performance Analysis Tool

MySQL profiling Performance Analysis Tool Brief description: MySQL Query Profiler is a very convenient Query diagnostic and analysis tool that can be used to obtain the consumption of multiple resources in a Query throughout the execution process,

ORA-00911 error resolution instance

ORA-00911 error resolution instance ORA-00911, "911" looked very domineering error number, although I am still a beginner of Oracle, but every time I encounter a not seen ORA error number, there is a kind of catch-up, based on the error code, OERR,

MySQL slow Query

MySQL slow Query Brief description: To analyze the query performance of MySQL statements, in addition to using the EXPLAIN command to output the execution plan, MySQL can also record the statements whose query exceeds the specified time, the SQL

Do you really understand the nosql world ?, Nosql world

Do you really understand the nosql world ?, Nosql world Recently, I want to sort out my nosql knowledge and some nosql databases. One is to deepen your understanding of nosql, and the other is to organize your knowledge to make it more

Customized tablespace retention policies and customized retention policies

Customized tablespace retention policies and customized retention policies In large databases, the recycle bin is large, and there is a lot of garbage. It is very slow to query tablespaces. To prevent accidental operations, it is impossible to add

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