[COMMENT string ] -- 表选项 -- 字符集 CHARSET = charset_name 如果表没有设定,则使用数据库字符集 -- 存储引擎 ENGINE = engine_name 表在管理数据时采用的不同的数据结构,结构不同会导致处理方式、提供的特性操作等不同 常见的引擎:InnoDB MyISAM Memory/Heap BDB Merg
CREATE NORMAL INDEX index_c2 ON t_example_index ( n2 ); -- 使用多列一起组成索引 CREATE INDEX index_c2 ON t_example_index ( n2,n3 );mysql>SHOW INDEX FROM t_example_index ;+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---...
A single-row subquery from a table or tables is not considered a constant. For example, if a subquery returns an integer to be compared to a DATETIME value, the comparison is done as two integers. The integer is not converted to a temporal value. To compare the operands as DATETIME value...
If the table has a multiple-column index, any leftmost prefix of the index can be used by the optimizer to look up rows. For example, if you have a three-column index on (col1, col2, col3), you have indexed search capabilities on (col1), (col1, col2), and (col1, col2, co...
SELECT * FROM users WHERE name ='Alice'AND email ='alice@example.com'; 如果name 和 email 列上有复合索引,查询速度会更快。 使用EXPLAIN 分析查询 EXPLAIN SELECT * FROM users WHERE name ='Alice'; 输出会显示查询是否使用了索引以及使用了哪个索引。
对于不熟悉的用户,可以按照下面流程操作:SHOW VARIABLES LIKE '%innodb%'; 会显示很多变量,找到选项innodb_file_per_table OFF,了解这个选项的写法后,直接将选项写入my.cnf中,my.cnf中的写法是:找到[mysqld]分区,添加一行innodb_file_per_table = 1 ,重启mysqld服务,然后SHOW GLOBAL VARIABLES LIKE '%innodb%'...
1.创建全文索引(FullText index) 旧版的MySQL的全文索引只能用在MyISAM表格的char、varchar和text的字段上。 不过新版的MySQL5.6.24上InnoDB引擎也加入了全文索引,所以具体信息要随时关注官网, 1.1. 创建表的同时创建全文索引 CREATE TABLE article ( id INT AUTO_INCREMENT NOT NULL PRIMARY KEY, ...
To use a WHERE clause with SHOW CHARACTER SET, you would refer to those column names. As an example, the following statement displays information about character sets for which the default collation contains the string 'japanese': mysql> SHOW CHARACTER SET WHERE `Default collation` LIKE '%japa...
(This may occur for bulk inserts or deletes, or someALTER TABLEstatements, for example.) If this happens, the statistics are collected using whatever valueinnodb_stats_methodormyisam_stats_methodhas at the time. Thus, if you collect statistics using one method, but the system variable is ...
package org.example; import java.sql.*; /** *第一个jJDBC的程序 * */ public class App { public static void main( String[] args ) throws ClassNotFoundException, SQLException { //查询语句 //1.加载驱动 Class.forName("com.mysql.jdbc.Driver");//固定写法,加载驱动 //2.用户信息和url /*...