MySQL basic three-value type, index

My 1am,1pm

Numeric type

1. Int (4)

2. Float (5,2)

3. Varchar (4)

Enum type

1. Enum (' female ', ' male ')

2. Set (' book ', ' Football ', ' A ' ....)

Constraint conditions

Null Default Extra

The default is allow default NULL

Not NULL default value

Key

Normal Index Index

Unique Indexes unique

PRIMARY Key PRIMARY Key

FOREIGN Key FOREIGN Key

Full-text index fulltext

View Index desc

Showindex from What is the difference between the two

CREATE index createindex xxx on table ();

UNIQUE INDEX

Delete index dropindex xxxx on table;

Build Table Specify index field

Primarykey alter TABLEXXX Modify Xcolumn ... primary key auto_increment

altertable XXX Add primary key ();

to remove the notice, first remove the auto_increment

altertable xxxx drop PRIMARY key;

Composite PRIMARY Key different when repeating, the table must be created

Foreign Key

1. the storage engine must be InnoDB

2. the field type must match the

3. the referenced field must be an indexed field

ForeignKey ( field ) References table ( field )

Onupdate Cascade on DELETE on cascade) Engine=innodb;

MySQL basic three-value type, index