简单地说，

Blank和null不同。

Null是纯粹与数据库相关的，而blank是与验证相关的(表单要求)。

如果null=True, Django将在数据库中存储空值为null。如果字段有blank=True，表单验证将允许输入空值。如果一个字段有blank=False，该字段将是必需的。

这就是ORM在Django 1.8中映射空白和空字段的方法

class Test(models.Model):
    charNull        = models.CharField(max_length=10, null=True)
    charBlank       = models.CharField(max_length=10, blank=True)
    charNullBlank   = models.CharField(max_length=10, null=True, blank=True)

    intNull         = models.IntegerField(null=True)
    intBlank        = models.IntegerField(blank=True)
    intNullBlank    = models.IntegerField(null=True, blank=True)

    dateNull        = models.DateTimeField(null=True)
    dateBlank       = models.DateTimeField(blank=True)
    dateNullBlank   = models.DateTimeField(null=True, blank=True)        

为PostgreSQL 9.4创建的数据库字段是:

CREATE TABLE Test (
  id              serial                    NOT NULL,

  "charNull"      character varying(10),
  "charBlank"     character varying(10)     NOT NULL,
  "charNullBlank" character varying(10),

  "intNull"       integer,
  "intBlank"      integer                   NOT NULL,
  "intNullBlank"  integer,

  "dateNull"      timestamp with time zone,
  "dateBlank"     timestamp with time zone  NOT NULL,
  "dateNullBlank" timestamp with time zone,
  CONSTRAINT Test_pkey PRIMARY KEY (id)
)

为MySQL 5.6创建的数据库字段是:

CREATE TABLE Test (
     `id`            INT(11)     NOT  NULL    AUTO_INCREMENT,

     `charNull`      VARCHAR(10) NULL DEFAULT NULL,
     `charBlank`     VARCHAR(10) NOT  NULL,
     `charNullBlank` VARCHAR(10) NULL DEFAULT NULL,

     `intNull`       INT(11)     NULL DEFAULT NULL,
     `intBlank`      INT(11)     NOT  NULL,
     `intNullBlank`  INT(11)     NULL DEFAULT NULL,

     `dateNull`      DATETIME    NULL DEFAULT NULL,
     `dateBlank`     DATETIME    NOT  NULL,
     `dateNullBlank` DATETIME    NULL DEFAULT NULL
)

这里有一个blank= True和null=True字段的示例

description = models.TextField(blank=True, null= True)

在这种情况下: blank = True:告诉我们的表单可以将description字段保留为空

and

null = True:告诉我们的数据库，在我们的db字段中记录一个空值并且不给出错误是可以的。

|| blank = True || null = True && blank = True

class TestModel(models.Model):
    field1 = models.CharField(max_length=100, null=True)
    field2 = models.CharField(max_length=100, blank=True)   # it's not a correct way
    field3 = models.CharField(max_length=100, null=True, blank=True)

数据库字段:MySQL

CREATE TABLE TestModel (
     `id`        INT(10)        NOT     NULL      AUTO_INCREMENT,

     `field1`    VARCHAR(100)   NULL    DEFAULT   NULL,
     `field2`    VARCHAR(100)   NOT     NULL,
     `field3`    VARCHAR(100)   NULL    DEFAULT   NULL,
)

case-01: null = True

db:   db   field is accepts null value
form: form field is `required`

NB: DB IS ACCEPTS NULL VALUE, BUT FORM FIELD IS REQUIRED. SO FORM IS 
SUBMITTED WHEN THIS FIELD HAVE SOME VALUE. it's good.

case-02: blank = True

db:   db   field is not accepts null value
form: form field is `optional`

NB: FORM IS VALID WITHOUT ANY VALUE, BUT DB IS NOT ACCEPTS NULL VALUE.
SO THE FORM IS SUBMITTED WITHOUT ANY VALUE THEN BOOM. it's worst.

case-03: null = True && blank = True

db:   db   field is accepts null value
form: form field is `optional`

NB: HERE FORM FIELD IS OPTIONAL & FORM IS VALID WITHOUT ANY VALUE 
& DB ALSO ACCEPTS NULL VALUE. SO, IT'S BEST TO USE `null=True && blank=True`

:)

简单的回答是:Null是数据库表，Blank是Django表单。

当你设置null=true时，如果字段没有填充，它将在你的数据库中设置为空。如果 你设置blank=true，它不会为该字段设置任何值。