PHP がデータベースに接続できない場合の対処方法

#mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 5.7.11 MySQL Community Server (GPL)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement.

mysql> STATUS
--------------
mysql  Ver 14.14 Distrib 5.7.11, for osx10.9 (x86_64) using  EditLine wrapper

Connection id:        8
Current database:    
Current user:        root@localhost
SSL:            Not in use
Current pager:        less
Using outfile:        ‘‘
Using delimiter:    ;
Server version:        5.7.11 MySQL Community Server (GPL)
Protocol version:    10
Connection:        Localhost via UNIX socket
Server characterset:    utf8
Db     characterset:    utf8
Client characterset:    utf8
Conn.  characterset:    utf8
UNIX socket:        /tmp/mysql.sock
Uptime:            8 days 15 hours 1 min 17 sec

Threads: 2  Questions: 21  Slow queries: 0  Opens: 114  Flush tables: 1  Open tables: 0  Queries per second avg: 0.000
--------------

pdo_mysql.default_socket=/tmp/mysql.sock  
mysql.default_socket=/tmp/mysql.sock  
mysqli.default_socket=/tmp/mysql.sock

[client]  
socket=/tmp/mysql.sock  
  
[mysqld]  
socket=/tmp/mysql.sock