8.3.5 Multiple-Column Indexes MySQL can create composite indexes (that is, indexes on multiple columns). An index may consist of up to 16 columns. For certain data types, you can index a prefix of the column (seeSection 8.3.4, “Column Indexes”). ...
可以使用以下语句为表添加索引: ALTERTABLEusersADDINDEXindex_name_age(name,age); 1. 类图 下面是一个简单的类图示例,展示了表、索引和列之间的关系: 10..*11..*TabletableNamecreateTable()addIndex()IndexindexNamecolumnscreateIndex()ColumncolumnNamecolumnType 甘特图 以下是一个简单的甘特图示例,展示了添加...
CREATE TABLE t1 ( id INT NOT NULL, uid INT NOT NULL, PRIMARY KEY (id) ) PARTITION BY RANGE (id) (PARTITION p0 VALUES LESS THAN(5) ENGINE = MyISAM DATA DIRECTORY='/tmp' INDEX DIRECTORY='/tmp', PARTITION p1 VALUES LESS THAN(10) ENGINE = MyISAM DATA DIRECTORY='/tmp' INDEX DIRECTOR...
They are not useful if the lookup does not start from the leftmost side of the indexed columns. For example, this index won’t help you find all people named Bill or all people born on a certain date, because those columns are not leftmost in the index. Likewise, you can’t use the ...
This variant on RANGE facilitates partition pruning for queries using range conditions on multiple columns (that is, having conditions such as WHERE a = 1 AND b < 10 or WHERE a = 1 AND b = 10 AND c < 10). It enables you to specify value ranges in multiple columns by using a list...
多列索引(Multiple-Column Index,又称联合索引、复合索引)顾名思义就是几个列共同组成一个索引。多列索引最多由16个列组成。多列索引遵守最左前缀原则。 最左前缀原则就是在查询数据时,以最左边的列为基准进行索引匹配。例如,有个索引mul_index(col1, col2, col3),在进行索引查询的时候,只有(col1)、(col...
多列索引(Multiple-Column Index,又称联合索引、复合索引)顾名思义就是几个列共同组成一个索引。多列索引最多由16个列组成。多列索引遵守最左前缀原则。 最左前缀原则就是在查询数据时,以最左边的列为基准进行索引匹配。例如,有个索引mul_index(col1, col2, col3),在进行索引查询的时候,只有(col1)、(col...
createdatabase bigdata29;createdatabase bigdata29DEFAULTCHARSET utf8COLLATEutf8_general_ci; 删除数据库:drop database 数据库名; 进入数据库(进入文件):use 数据库; 示例: # 1.登录MySQL[root@master ~]# mysql -uroot -p123456mysql: [Warning] Using a password on thecommandline interface can be ...
-- 1. 创建新表结构 CREATE TABLE new_table LIKE old_table; -- 2. 复制数据 INSERT INTO new_table SELECT * FROM old_table; 3.5 其他 -- 查看所有表 show tables; -- 查看表结构 desc tableName; show columns from tableName; describe tableName; show create table tableName; ©...
也可以使用`DESCRIBE`或`DESC`命令来查看表结构,效果与`SHOW COLUMNS`相同: ```sql -- 查看表结构 DESCRIBE 表名; DESC 表名; -- 示例:查看'students'表的结构 DESCRIBE students; DESC students; ``` 有关约束 ### 添加主键(Primary Key) - **创建表时添加主键**: ...