创建表
简单的方式
代码如下:
CREATE TABLE person (
number INT(11),
name VARCHAR(255),
birthday DATE
);
或者是
代码如下:
CREATE TABLE IF NOT EXISTS person (
number INT(11),
name VARCHAR(255),
birthday DATE
);
查看mysql创建表:
代码如下:
SHOW CREATE table person;
CREATE TABLE `person` (
`number` int(11) DEFAULT NULL,
`name` varchar(255) DEFAULT NULL,
`birthday` date DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
查看表所有的列:
代码如下:
SHOW FULL COLUMNS from person;
+----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment |
+----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| number | int(11) | NULL | YES | | NULL | | select,insert,update,references | |
| name | varchar(255) | utf8_general_ci | YES | | NULL | | select,insert,update,references | |
| birthday | date | NULL | YES | | NULL | | select,insert,update,references | |
+----------+--------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
创建临时表:
代码如下:
CREATE TEMPORARY TABLE temp_person (
number INT(11),
name VARCHAR(255),
birthday DATE
);
在创建表格时,您可以使用TEMPORARY关键词。只有在当前连接情况下,TEMPORARY表才是可见的。当连接关闭时,TEMPORARY表被自动取消。这意味着两个不同的连接可以使用相同的临时表名称,同时两个临时表不会互相冲突,也不与原有的同名的非临时表冲突。(原有的表被隐藏,直到临时表被取消时为止。)您必须拥有CREATE TEMPORARY TABLES权限,才能创建临时表。
如果表已存在,则使用关键词IF NOT EXISTS可以防止发生错误。
代码如下:
CREATE TABLE IF NOT EXISTS person2 (
number INT(11),
name VARCHAR(255),
birthday DATE
);
注意,原有表的结构与CREATE TABLE语句中表示的表的结构是否相同,这一点没有验证。注释:如果您在CREATE TABLE...SELECT语句中使用IF NOT EXISTS,则不论表是否已存在,由SELECT部分选择的记录都会被插入。
在CREATE TABLE语句的末尾添加一个SELECT语句,在一个表的基础上创建表
代码如下:
CREATE TABLE new_tbl SELECT * FROM orig_tbl;
注意,用SELECT语句创建的列附在表的右侧,而不是覆盖在表上。
代码如下:
mysql> SELECT * FROM foo;
+---+
| n |
+---+
| 1 |
+---+
mysql> CREATE TABLE bar (m INT) SELECT n FROM foo;
mysql> SELECT * FROM bar;
+------+---+
| m | n |
+------+---+
| NULL | 1 |
+------+---+
也可以明确地为一个已生成的列指定类型
代码如下:
CREATE TABLE foo (a TINYINT NOT NULL) SELECT b+1 AS a FROM bar;
根据其它表的定义(包括在原表中定义的所有的列属性和索引),使用LIKE创建一个空表:
代码如下:
CREATE TABLE new_tbl LIKE orig_tbl;
创建一个有主键,唯一索引,普通索引的表:
代码如下:
CREATE TABLE `people` (
`peopleid` smallint(6) NOT NULL AUTO_INCREMENT,
`firstname` char(50) NOT NULL,
`lastname` char(50) NOT NULL,
`age` smallint(6) NOT NULL,
`townid` smallint(6) NOT NULL,
PRIMARY KEY (`peopleid`),
UNIQUE KEY `unique_fname_lname`(`firstname`,`lastname`),
KEY `fname_lname_age` (`firstname`,`lastname`,`age`)
) ;
其中peopleid是主键,以firstname和lastname两列建立了一个唯一索引,以firstname,lastname,age三列建立了一个普通索引
删除表
代码如下:
DROP TABLE tbl_name;
或者是
代码如下:
DROP TABLE IF EXISTS tbl_name;

MySQL functions can be used for data processing and calculation. 1. Basic usage includes string processing, date calculation and mathematical operations. 2. Advanced usage involves combining multiple functions to implement complex operations. 3. Performance optimization requires avoiding the use of functions in the WHERE clause and using GROUPBY and temporary tables.

Efficient methods for batch inserting data in MySQL include: 1. Using INSERTINTO...VALUES syntax, 2. Using LOADDATAINFILE command, 3. Using transaction processing, 4. Adjust batch size, 5. Disable indexing, 6. Using INSERTIGNORE or INSERT...ONDUPLICATEKEYUPDATE, these methods can significantly improve database operation efficiency.

In MySQL, add fields using ALTERTABLEtable_nameADDCOLUMNnew_columnVARCHAR(255)AFTERexisting_column, delete fields using ALTERTABLEtable_nameDROPCOLUMNcolumn_to_drop. When adding fields, you need to specify a location to optimize query performance and data structure; before deleting fields, you need to confirm that the operation is irreversible; modifying table structure using online DDL, backup data, test environment, and low-load time periods is performance optimization and best practice.

Use the EXPLAIN command to analyze the execution plan of MySQL queries. 1. The EXPLAIN command displays the execution plan of the query to help find performance bottlenecks. 2. The execution plan includes fields such as id, select_type, table, type, possible_keys, key, key_len, ref, rows and Extra. 3. According to the execution plan, you can optimize queries by adding indexes, avoiding full table scans, optimizing JOIN operations, and using overlay indexes.

Subqueries can improve the efficiency of MySQL query. 1) Subquery simplifies complex query logic, such as filtering data and calculating aggregated values. 2) MySQL optimizer may convert subqueries to JOIN operations to improve performance. 3) Using EXISTS instead of IN can avoid multiple rows returning errors. 4) Optimization strategies include avoiding related subqueries, using EXISTS, index optimization, and avoiding subquery nesting.

Methods for configuring character sets and collations in MySQL include: 1. Setting the character sets and collations at the server level: SETNAMES'utf8'; SETCHARACTERSETutf8; SETCOLLATION_CONNECTION='utf8_general_ci'; 2. Create a database that uses specific character sets and collations: CREATEDATABASEexample_dbCHARACTERSETutf8COLLATEutf8_general_ci; 3. Specify character sets and collations when creating a table: CREATETABLEexample_table(idINT

To safely and thoroughly uninstall MySQL and clean all residual files, follow the following steps: 1. Stop MySQL service; 2. Uninstall MySQL packages; 3. Clean configuration files and data directories; 4. Verify that the uninstallation is thorough.

Renaming a database in MySQL requires indirect methods. The steps are as follows: 1. Create a new database; 2. Use mysqldump to export the old database; 3. Import the data into the new database; 4. Delete the old database.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

SublimeText3 Linux new version
SublimeText3 Linux latest version

SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

SublimeText3 Chinese version
Chinese version, very easy to use

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool
