laravel 5.4 指定的key太长，为什么数字191

发布于05月08日

我知道这个问题已经被讨论、解决或解决了

Schema::defaultStringLength(191);

I tried: if 192, wrong. 191, ok. After this, I also edit database\migrations\xxx_user_table.php
Change this

$table->string('name');

成为

$table->string('name', 255);

然后运行php artisan迁移，就可以了.

我看到了这些文章

还有这个: @https://dev.mysql.com/doc/refman/5.7/en/innodb-restrictions.html

对于符合以下条件的InnoDB表，索引键前缀长度限制为767字节使用冗余或紧凑行格式.例如，您可能会点击上的列前缀索引超过255个字符时的此限制 TEXT或VARCHAR列，假定为utf8mb3字符集和每个字符最多3个字节.

但为什么名字的长度255是可以的呢

Why is it limited to 191 characters?

The key is that Laravel 5.4 defaults to utf8mb4 so the database assumes a maximum of 4 bytes for each character.

'charset' => 'utf8mb4',
'collation' => 'utf8mb4_unicode_ci',

如果对utf8mb4进行了更新，那么您所引用的示例将完美匹配.Emphasis在编辑处添加.

The index key prefix length limit is 767 bytes for InnoDB tables that use the REDUNDANT or COMPACT row format. For example, you might hit this limit with a column prefix index of more than 191 characters on a TEXT or VARCHAR column, assuming a utf8mb4 character set and the maximum of 4 bytes for each character.

191 * 4 = 764(作品)
192 * 4 = 768 (too large)

utf8mb4引入了对Supplementary Characters的支持，这不是utf8的一部分，其中包括表情符号.为了进一步了解你是否需要utf8mb4，你可以从this StackOverflow answer on the question开始.

How do I fix this?

如果需要保持较大的字段大小，最快的修复方法是将默认值改为utf8.Laravel 5.3 and below defaulted utf8, and that would be safe to use in most cases.

'charset' => 'utf8',
'collation' => 'utf8_unicode_ci',

Alternatively, you can set the charset and collation on specific tables in the DB Migration when creating that table. That would look something like this:

Schema::create('monitors', function (Blueprint $table) {
    $table->charset = 'utf8';
    $table->collation = 'utf8_unicode_ci';

    $table->increments('id');
    $table->string('myString')->unique();
});