View Index
SHOW INDEX from database table name
For example: SHOW INDEX from Order_info;
Add index
ALTER TABLE Database add index index name (database field name)
Primary key Index
ALTER TABLE ' table_name ' ADD PRIMARY KEY (' column ')
For example: ALTER TABLE order_info ADD PRIMARY KEY (order_id);
Unique (single index)
ALTER TABLE ' table_name ' ADD UNIQUE (' column ')
Index (normal index)
Mysql>alter TABLE ' table_name ' ADD INDEX index_name (' column ')
Fulltext (full-text index)
ALTER TABLE ' table_name ' ADD fulltext (' column ')
Multi-column Index
ALTER TABLE ' table_name ' ADD index index_name (' Column1 ', ' column2 ', ' Column3 ') 1. Normal index.
This is the most basic index and it has no limitations. It is created in the following ways:
(1) Creating index: Create index IndexName on TableName (tablecolumns (length)); if it is a Char,varchar type, length can be less than the actual length of the field, if it is blob and TEXT Type, the same length must be specified.
(2) Modify table structure: ALTER tableName ADD INDEX [IndexName] On (tablecolumns (length))
(3) directly specify when creating the table: Create TABLE TableName ([...], INDEX [IndexName] (tablecolumns (length));
2. Unique index.
It is similar to the previous "normal index", except that the value of the indexed column must be unique, but it allows for a null value. If it is a composite index, the combination of column values must be unique. It is created in the following ways:
(1) Creating an index: Create UNIQUE index indexname on tableName (tablecolumns (length))
(2) Modify table structure: ALTER tableName ADD UNIQUE [IndexName] On (tablecolumns (length))
(3) directly specify when creating the table: Create TABLE TableName ([...], UNIQUE [IndexName] (tablecolumns (length));
3. Primary KEY index
It is a special unique index and is not allowed to have null values. The primary key index is typically created at the same time as the table is built: Create TABLE Testindex (I_testid INT not NULL auto_increment,vc_name VARCHAR (+) not null,primary KEY (i _testid)); Of course, you can also use the ALTER command.
MySQL add primary key, index
