MySQL Study之--MySQL工具mysqlshow mmysqlshow客户可用来很快地查找存在哪些数据库,数据库中的表,表中的列或索 mysqlshow为一些SQL显示语句提供了一个命令行界面。相同的信息可以通过直接使用那些语句获得。例如,你可以从mysql客户程序发出它们。 象这样调用mysqlshow:shell> mysqlshow[选项] [db_name [tbl_name [col_name]]
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案例:
[root@mysrv mysql]# mysqlshow --help mysqlshow Ver 9.10 Distrib 5.1.66, for redhat-linux-gnu (x86_64) Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Shows the structure of a MySQL database (databases, tables, and columns). Usage: mysqlshow [OPTIONS] [database [table [column]]] If last argument contains a shell or SQL wildcard (*,?,% or _) then only what's matched by the wildcard is shown. If no database is given then all matching databases are shown. If no table is given, then all matching tables in database are shown. If no column is given, then all matching columns and column types in table are shown. Default options are read from the following files in the given order: /etc/mysql/my.cnf /etc/my.cnf ~/.my.cnf The following groups are read: mysqlshow client The following options may be given as the first argument: --print-defaults Print the program argument list and exit. --no-defaults Don't read default options from any option file. --defaults-file=# Only read default options from the given file #. --defaults-extra-file=# Read this file after the global files are read. -c, --character-sets-dir=name Directory for character set files. --default-character-set=name Set the default character set. --count Show number of rows per table (may be slow for non-MyISAM tables). -C, --compress Use compression in server/client protocol. -#, --debug[=name] Output debug log. Often this is 'd:t:o,filename'. --debug-check Check memory and open file usage at exit. --debug-info Print some debug info at exit. -?, --help Display this help and exit. -h, --host=name Connect to host. -i, --status Shows a lot of extra information about each table. -k, --keys Show keys for table. -p, --password[=name] Password to use when connecting to server. If password is not given, it's solicited on the tty. -P, --port=# Port number to use for connection or 0 for default to, in order of preference, my.cnf, $MYSQL_TCP_PORT, /etc/services, built-in default (3306). --protocol=name The protocol to use for connection (tcp, socket, pipe, memory). -t, --show-table-type Show table type column. -S, --socket=name The socket file to use for connection. --ssl Enable SSL for connection (automatically enabled with other flags).Disable with --skip-ssl. --ssl-ca=name CA file in PEM format (check OpenSSL docs, implies --ssl). --ssl-capath=name CA directory (check OpenSSL docs, implies --ssl). --ssl-cert=name X509 cert in PEM format (implies --ssl). --ssl-cipher=name SSL cipher to use (implies --ssl). --ssl-key=name X509 key in PEM format (implies --ssl). --ssl-verify-server-cert Verify server's "Common Name" in its cert against hostname used when connecting. This option is disabled by default. -u, --user=name User for login if not current user. -v, --verbose More verbose output; you can use this multiple times to get even more verbose output. -V, --version Output version information and exit. Variables (--variable-name=value) and boolean options {FALSE|TRUE} Value (after reading options) --------------------------------- ----------------------------- character-sets-dir (No default value) default-character-set latin1 count FALSE compress FALSE debug-check FALSE debug-info FALSE host (No default value) status FALSE keys FALSE port 3306 show-table-type FALSE socket /tmp/mysql.sock ssl FALSE ssl-ca (No default value) ssl-capath (No default value) ssl-cert (No default value) ssl-cipher (No default value) ssl-key (No default value) ssl-verify-server-cert FALSE user (No default value)<strong> </strong>
1、不指定查看的database
[root@mysrv mysql]# mysqlshow -uroot -poracle
+--------------------+
| Databases |
+--------------------+
| information_schema |
| mysql |
| mysqlslap |
| performance_schema |
| prod |
| sakila |
| test |
+--------------------+
2、指定查看的database
[root@mysrv mysql]# mysqlshow -uroot -poracle mysql
Database: mysql
+---------------------------+
| Tables |
+---------------------------+
| columns_priv |
| db |
| event |
| func |
| general_log |
| help_category |
| help_keyword |
| help_relation |
| help_topic |
| host |
| innodb_index_stats |
| innodb_table_stats |
| ndb_binlog_index |
| plugin |
| proc |
| procs_priv |
| proxies_priv |
| servers |
| slave_master_info |
| slave_relay_log_info |
| slave_worker_info |
| slow_log |
| tables_priv |
| time_zone |
| time_zone_leap_second |
| time_zone_name |
| time_zone_transition |
| time_zone_transition_type |
| user |
+---------------------------+
[root@mysrv mysql]# mysqlshow -uroot -poracle prod
Database: prod
+--------+
| Tables |
+--------+
| t1 |
| t2 |
| t3 |
| t4 |
+--------+
3、查看指定
[root@mysrv mysql]# mysqlshow -uroot -poracle prod t1Database: prod Table: t1
+-------+-------------+-------------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment |
+-------+-------------+-------------------+------+-----+---------+-------+---------------------------------+---------+
| id | int(11) | | NO | PRI | 0 | | select,insert,update,references | |
| name | varchar(10) | latin1_swedish_ci | YES | | | | select,insert,update,references | |
+-------+-------------+-------------------+------+-----+---------+-------+---------------------------------+---------+

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB

MySQL/InnoDB supports four transaction isolation levels: ReadUncommitted, ReadCommitted, RepeatableRead and Serializable. 1.ReadUncommitted allows reading of uncommitted data, which may cause dirty reading. 2. ReadCommitted avoids dirty reading, but non-repeatable reading may occur. 3.RepeatableRead is the default level, avoiding dirty reading and non-repeatable reading, but phantom reading may occur. 4. Serializable avoids all concurrency problems but reduces concurrency. Choosing the appropriate isolation level requires balancing data consistency and performance requirements.

MySQL is suitable for web applications and content management systems and is popular for its open source, high performance and ease of use. 1) Compared with PostgreSQL, MySQL performs better in simple queries and high concurrent read operations. 2) Compared with Oracle, MySQL is more popular among small and medium-sized enterprises because of its open source and low cost. 3) Compared with Microsoft SQL Server, MySQL is more suitable for cross-platform applications. 4) Unlike MongoDB, MySQL is more suitable for structured data and transaction processing.

MySQL index cardinality has a significant impact on query performance: 1. High cardinality index can more effectively narrow the data range and improve query efficiency; 2. Low cardinality index may lead to full table scanning and reduce query performance; 3. In joint index, high cardinality sequences should be placed in front to optimize query.

The MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.

MySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.


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