此问题在此处已有答案：

MySQL Error #1071 - Specified key was too long; max key length is 767 bytes（37个答案）
三年前就关门了。
下面的代码：

<?php

use yii\db\Migration;

/**
 * Handles the creation of table `account`.
 */
class m180110_204953_create_account_table extends Migration
{
    /**
     * @inheritdoc
     */
    public function up()
    {
        $this->createTable('account', [
            'id' => $this->primaryKey(),
            'username' => $this->string()->notNull()->unique(),
            'profile_pic_url' => $this->string(),
            'full_name' => $this->string(),
            'biography' => $this->string(),
            'external_url' => $this->string(),
            'instagram_id' => $this->string(),
            'updated_at' => $this->dateTime(),
            'created_at' => $this->dateTime(),
            'monitoring' => $this->boolean()->notNull()->defaultValue(0),
        ]);
    }

    /**
     * @inheritdoc
     */
    public function down()
    {
        $this->dropTable('account');
    }
}

在运行此命令后，我得到了以下结果：

***applying m180110_204953_create_account_table

    > create table account ...Exception 'yii\db\Exception' with message 'SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 767 bytes
The SQL being executed was: CREATE TABLE `account` (
    `id` int(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
    `username` varchar(255) NOT NULL UNIQUE,
    `profile_pic_url` varchar(255),
    `full_name` varchar(255),
    `biography` varchar(255),
    `external_url` varchar(255),
    `instagram_id` varchar(255),
    `updated_at` datetime,
    `created_at` datetime,
    `monitoring` tinyint(1) NOT NULL DEFAULT 0
)'

in /root/ig-monitoring/vendor/yiisoft/yii2/db/Schema.php:664

Error Info:
Array
(
    [0] => 42000
    [1] => 1071
    [2] => Specified key was too long; max key length is 767 bytes
)

Stack trace:

# 0 /root/ig-monitoring/vendor/yiisoft/yii2/db/Command.php(1295): yii\db\Schema->convertException(Object(PDOException), 'CREATE TABLE `a...')

# 1 /root/ig-monitoring/vendor/yiisoft/yii2/db/Command.php(1091): yii\db\Command->internalExecute('CREATE TABLE `a...')

# 2 /root/ig-monitoring/vendor/yiisoft/yii2/db/Migration.php(323): yii\db\Command->execute()

# 3 /root/ig-monitoring/migrations/m180110_204953_create_account_table.php(25): yii\db\Migration->createTable('account', Array)

# 4 /root/ig-monitoring/vendor/yiisoft/yii2/console/controllers/BaseMigrateController.php(725): m180110_204953_create_account_table->up()

# 5 /root/ig-monitoring/vendor/yiisoft/yii2/console/controllers/BaseMigrateController.php(199): yii\console\controllers\BaseMigrateController->migrateUp('m180110_204953_...')

# 6 [internal function]: yii\console\controllers\BaseMigrateController->actionUp(0)

# 7 /root/ig-monitoring/vendor/yiisoft/yii2/base/InlineAction.php(57): call_user_func_array(Array, Array)

# 8 /root/ig-monitoring/vendor/yiisoft/yii2/base/Controller.php(157): yii\base\InlineAction->runWithParams(Array)

# 9 /root/ig-monitoring/vendor/yiisoft/yii2/console/Controller.php(148): yii\base\Controller->runAction('', Array)

# 10 /root/ig-monitoring/vendor/yiisoft/yii2/base/Module.php(528): yii\console\Controller->runAction('', Array)

# 11 /root/ig-monitoring/vendor/yiisoft/yii2/console/Application.php(180): yii\base\Module->runAction('migrate', Array)

# 12 /root/ig-monitoring/vendor/yiisoft/yii2/console/Application.php(147): yii\console\Application->runAction('migrate', Array)

# 13 /root/ig-monitoring/vendor/yiisoft/yii2/base/Application.php(386): yii\console\Application->handleRequest(Object(yii\console\Request))

# 14 /root/ig-monitoring/yii(19): yii\base\Application->run()

# 15 {main}

有什么办法解决这个问题吗？