Looks like mysqld is not started . Run the following command to fix the issue.
service mysqld start
Tag Archives: MySQL
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver on eclipse
You need to add jar file to build path
right click on project->build path->configure build path->libraries tab ->add external jar
browse it and add it.
after adding also if u not getting same error, then
You must include the jar file in the Deployment Assembly of the Project.
1)select the web project which contains the jsp file
2)select Project tab in the menubar in Eclipse
3)select properties in the drop down menu
4)select Deployment Assembly
5)Add your ojdbc6.jar file in it..
Enable MySQL Query Caching
You can setup them in /etc/my.cnf (CentOS 7)
vi /etc/my.cnf
Append config directives as follows:
query_cache_size = 268435456 query_cache_type=1 query_cache_limit=1048576
In above example the maximum size of individual query results that can be cached set to 1048576 using query_cache_limit system variable. Memory size in Kb.
Restart the mysql service.
service mysqld restart
Install MySQL Linux CentOS
Download Package
yum localinstall https://dev.mysql.com/get/mysql57-community-release-el7-9.noarch.rpm -y
Install MySQL
yum install mysql-community-server -y
Start MySQL
service mysqld start service mysqld status
Generate Temporary password
grep 'temporary password' /var/log/mysqld.log
Login To MySQL
mysql -uroot -p
Reset Password and set Privilages
ALTER USER 'root'@'localhost' IDENTIFIED BY 'Root@123'; GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY 'Root@123' WITH GRANT OPTION; FLUSH PRIVILEGES;
Open MySQL Port 3306
firewall-cmd --zone=public --add-port=3306/tcp --permanent firewall-cmd --reload firewall-cmd --list-all
Prepared Statements MySQL
Similar in concept to templates – contain compiled code used to run common sql operations
o Advantages:
Query only parsed once, but allows for multiple executions, with same or different parameters (performance consideration)
Related parameters do not need to be quoted (security consideration)
o Only feature pdo will emulate for adapters that do not support prepared statements
mysqli_real_escape_string
The mysqli_real_escape_string() function escapes special characters in a string for use in an SQL statement
Transactions
• Combines individual sql operations into one
• Usually start with begin or begin transaction
• Execute the transaction using commit
• Cancel the transaction using rollback
Example
START TRANSACTION; SELECT @A:=SUM(salary) FROM table1 WHERE type=1; UPDATE table2 SET summary=@A WHERE type=1; COMMIT;
Unbuffered Queries
Unbuffered MySQL queries execute the query and then return a resource while the data is still waiting on the MySQL server for being fetched. This uses less memory on the PHP-side, but can increase the load on the server. Unless the full result set was fetched from the server no further queries can be sent over the same connection. Unbuffered queries can also be referred to as “use result”.
Not able to login magento 2 Memcached
Customers and admin are not able to login to magento 2 when memcached is enabled and to fix it increase the default value of innodb_buffer_pool_size in my.ini
MySQL Cursor
A cursor can’t be used by itself in MySQL. It is an essential component in stored procedures. I would be inclined to treat a cursor as a “pointer” in C/C++, or an iterator in PHP’s foreach statement.
With cursors, we can traverse a dataset and manipulate each record to accomplish certain tasks. When such an operation on a record can also be done in the PHP layer, it saves data transfer amounts as we can just return the processed aggregation/statistical result back to the PHP layer (thus eliminating the select – foreach – manipulation process at the client side).
Since a cursor is implemented in a stored procedure, it has all the benefits (and limitations) of an SP (access control, pre-compiled, hard to debug, etc).
MySQL supports cursors inside stored programs. The syntax is as in embedded SQL. Cursors have these properties:
Asensitive: The server may or may not make a copy of its result table
Read only: Not updatable
Nonscrollable: Can be traversed only in one direction and cannot skip rows
Cursor declarations must appear before handler declarations and after variable and condition declarations.