80 此值表示mysql将使用覆盖索引,以避免访问表。不要把覆盖索引和index访问类型弄混了。 81 “Using where” 82 这意味着mysql服务器将在存储引擎检索行后再进行过滤,许多where条件里涉及索引中的列,当(并且如果)它读取索引时,就能被存储引擎检验,因此不是所有带where子句的查询都会显示“Using where”。有时“Usin...
In MySQL, an index can be created on a table when the table is created with CREATE TABLE command. Otherwise, CREATE INDEX enables to add indexes to existing tables. A multiple-column index can be created using multiple columns. The indexes are formed by concatenating the values of the given...
ALTER TABLE table_name ADD [UNIQUE | FULLTEXT | SPATIAL] [INDEX | KEY] [index_name] (col_name[length],...) [ASC | DESC] 1. 2. 2.使用CREATE INDEX创建索引 CREATE INDEX语句可以在已经存在的表上添加索引,在MySQL中,CREATE INDEX被映射到一个ALTER TABLE语句上,基本语法结构为: CREATE [UNIQUE...
In another attempt I created table with index and load 10M row at a time. All attempts show exponential behavior on index creation. I have tried other process monitor (gkrellm and top) . They all show memory is not the bottle neck and disk IO is heavy but not major cause, put CPU is...
MySQL CREATE TABLE is used to create a table within a database. MySQL represents each table by a .frm table format (definition) file in the database directory. The storage engine might create other files as well for the table. The storage engine creates data and index files. The table fo...
TABLE SELECT and CREATE TABLE with INDEX/DATA DIRECTOY options). The problem of bugs 4968, 19733, 19282 and 6895 was that functions mysql_prepare_table, mysql_create_table and mysql_alter_table are not re-execution friendly: during their operation they modify contents of LEX (members create_...
MySQL中可以使用alter table这个SQL语句来为表中的字段添加索引。 使用alter table语句来为表中的字段添加索引的基本语法是: ALTER TABLE <表名> ADD INDEX (<字段>); 我们来尝试为test中t_name字段添加一个索引。 mysql> alter table test add index(t_name); ...
例如,CREATE TABLE用于创建新表,CREATE DATABASE用于创建新数据库,CREATE VIEW用于创建视图,CREATE INDEX用于创建索引。其中,最常见的用途是创建表,通过定义表的列和数据类型来结构化存储数据。创建一个表的过程不仅包括定义列的名称和数据类型,还可以包括约束条件,如主键、外键、唯一约束等,从而确保数据的完整性和一致...
CREATE UNIQUE INDEX index_name ON table_name (column1, column2, ...); MySQL CREATE INDEX ExampleThe SQL statement below creates an index named "idx_lastname" on the "LastName" column in the "Persons" table:CREATE INDEX idx_lastname ON Persons (LastName); ...
Temporary table: no Number of attributes: 7 Number of primary keys: 1 Length of frm data: 296 Row Checksum: 1 Row GCI: 1 SingleUserMode: 0 ForceVarPart: 1 FragmentCount: 2 TableStatus: Retrieved -- Attributes -- A Date NOT NULL AT=FIXED ST=DISK ...