Rails代码:

ruby-1.9.2-p290 :099 > ActiveRecord::Base.connection.execute("USE INFORMATION_SCHEMA")

ruby-1.9.2-p290 :099 > ActiveRecord::Base.connection.execute("SELECT SCHEMA_NAME FROM         INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = 'entos_development'").to_a
SQL (0.2ms) SELECT SCHEMA_NAME FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME =               'entos_development'
=> [["entos_development"]] 
ruby-1.9.2-p290 :100 > ActiveRecord::Base.connection.execute("SELECT SCHEMA_NAME FROM              INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = 'entos_development1'").to_a
SQL (0.3ms) SELECT SCHEMA_NAME FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME =            'entos_development1'
=> []

=> entos_development存在，entos_development1不存在

另一个php解决方案，但与PDO:

<?php
try {
   $pdo = new PDO('mysql:host=localhost;dbname=dbname', 'root', 'password', [ PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION ]);
   echo 'table dbname exists...';
}
catch (PDOException $e) {
   die('dbname not found...');
}

有了这个脚本，你可以得到是否数据库存在，如果它不存在，它不会抛出异常。

SELECT 
    IF(EXISTS( SELECT 
                SCHEMA_NAME
            FROM
                INFORMATION_SCHEMA.SCHEMATA
            WHERE
                SCHEMA_NAME = 'DbName'),
        'Yes',
        'No')  as exist

当您没有足够权限查看数据库时，使用INFORMATION_SCHEMA或show数据库是不可靠的。当您无法访问数据库时，它似乎不存在。创建之后就会失败。另一种更精确的检查方法是使用use命令的输出，尽管我不知道这种方法有多可靠(文本输出在未来版本/其他语言中会有变化……)，所以请注意。

CHECK=$(mysql -sNe "use DB_NAME" 2>&1)
if [ $? -eq 0 ]; then
  # database exists and is accessible
elif [ ! -z "$(echo $CHECK | grep 'Unknown database')" ]; then
  # database does not exist
elif [ ! -z "$(echo $CHECK | grep 'Access denied')" ]; then
  # cannot tell if database exists (not enough permissions)"
else
  # unexpected output
fi

SELECT COUNT(*) FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = 'DbName'

1 -存在，0 -不存在

使用bash:

if [ "`mysql -u'USER' -p'PASSWORD' -se'USE $DATABASE_NAME;' 2>&1`" == "" ]; then
    echo $DATABASE_NAME exist
else
    echo $DATABASE_NAME doesn't exist
fi