Category Archives: MySQL

CommunicationsException: Communications link failure [How to Solve]

Today, when I was learning mybatis, I always reported an error when executing the query operation! The error is as follows:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

It probably means that there is a problem with the database connection. After checking the database name, user name and password, there are no errors. Some blogs say that they need to change the MySQL configuration file. I really think it’s too troublesome to change

Solution:

A blog commented that if MySQL is version 8.0 or above, usessl in the configuration should be set to false
and then it will be

useSSL=true

How to Solve Mysql8 load data error

First, when executing the load data command, a message appears, loading local data is disabled; this must be enabled on both the client and server sides
Set needs to be set on the server side   local_infile=1

And set MySQL — local infile = 1 – uroot – P when connecting to the client

The MySQL server is running with the –secure-file-priv option so it cannot execute this statement

The mysql.ini file already exists in the installed MySQL directory. You need to create a new my.ini file and add

[mysqld]
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M

# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
secure-file-priv=

 

[Solved] ERROR 1396 (HY000): Operation ALTER USER failed for ‘root‘@‘localhost‘

MySQL Connect database error:
1251 client does not support authentication protocol requested by server; consider upgrading Mysql client ERROR 1396 (HY000): Operation ALTER USER failed for ‘root’@’localhost’

Pre-registered mysql

mysql -u root -p

Input password

mysql> use mysql;
mysql> select user,host from user;

Note that my root and host are ‘%’
you may execute:

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'root';

Change to:

ALTER USER 'root'@'%' IDENTIFIED WITH mysql_native_password BY 'root';

Operation record:

mysql> ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'root';
ERROR 1396 (HY000): Operation ALTER USER failed for 'root'@'localhost'
mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> select user,host from user;
+------------------+-----------+
| user             | host      |
+------------------+-----------+
| root             | %         |
| mysql.infoschema | localhost |
| mysql.session    | localhost |
| mysql.sys        | localhost |
+------------------+-----------+
4 rows in set (0.00 sec)

mysql> ALTER USER 'root'@'%' IDENTIFIED WITH mysql_native_password BY 'root';
Query OK, 0 rows affected (0.00 sec)

mysql> quit
Bye

Mysql ERROR 1067: Invalid default value for ‘date’ [How to Solve]

When adding fields to a table, I suddenly find that the default value of a field of date type is wrong, which is depressing~

After troubleshooting, it turns out that there is a problem with MySQL configuration. Under Wamp, SQL is not set in MySQL 5.7_ Mode.

1. Find [mysqld] in my.ini file

2. If there is no SQL_Mode, add it and modify it if necessary

sql_mode="STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION"
or
sql_mode=ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

3.Restart MySQL;
use the following commands to operate mysql:
systemctl restart mysqld.service
systemctl start mysqld.service
systemctl stop mysqld.service

MySQL server has gone away Error [How to Solve]

Reference: solution to MySQL server has gone away error – time blog
When we use Mysql to import large file SQL, we may report the MySQL server has gone away error. The problem is the default value setting of  max_allowed_packet configuration is too small. You only need to increase the value of this item and import it again to succeed. This item is used to limit the size of the package received by the MySQL server. Therefore, if the imported file is too large, it may exceed the value set in this item, resulting in unsuccessful import! Let’s take a look at how to view and set the value of this item.

View the value of Max_allowed_packet

show global variables like 'max_allowed_packet';


+--------------------+---------+
| Variable_name      | Value   |
+--------------------+---------+
| max_allowed_packet | 4194304 |
+--------------------+---------+

You can see that the size of this item is only 4m by default. Next, set the value to 150m (1024 * 1024 * 150)

set global max_allowed_packet=157286400;

View the size again

show global variables like 'max_allowed_packet';

By increasing this value, generally speaking, importing SQL with a large amount of data should be successful again. If an error is still reported, continue to increase it. Please note that setting in the command line is only valid for the current time. After restarting the MySQL service, restore the default value, but you can modify the configuration file (you can add max_allowed_packet = 150m in the configuration file my.cnf) To achieve the purpose of permanent validity, but in fact, we do not often import such a large amount of data, so I think the current configuration can take effect through the command, and there is no need to modify the configuration file.

Oracle Database AWR error: ORA-06502 [How to Solve]

Oracle database AWR report is an important tool for DBA to analyze database performance!

Recently encountered a problem and reported an error:

ERROR:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at "SYS.DBMS_WORKLOAD_REPOSITORY", line 919
ORA-06512: at line 1

So, how to solve this problem?

Solution:

update WRH$_SQLTEXT set sql_text = SUBSTR(sql_text, 1, 1000);
commit;

After execution, re execute sqlplus/as SYSDBA @/ RDMBS/admin/awrrpt. SQL script successfully generates AWR report!

This sharing is over~

[Solved] Error: read ECONNRESET at TCP.onStreamRead Cannot enqueue Query after fatal error

Error analysis

This error often occurs when I use node to connect to MySQL. I wonder if it is because I do not close the connection every time I query the database after creating a MySQL connection, so the database is always connected and does not respond for a long time, resulting in the following error
error1:

error2:

 

Solution:

error1:

const mysql = require('mysql');
const connInfo = require('./config');

function queryMysql(sql, callback){
    const conn = mysql.createConnection(connInfo)
    conn.query(sql, (err, result)=>{
        if(err){
            console.log(err);
        }else {
            callback(result)
        }
        conn.end(err => {
            if(err){
                console.log(err)
            }
        })
    })
}

module.exports = queryMysql;

Error2:
We only need to configure useConnectionPooling : true when instantiating SessionStore . for example:

var sessionStore = new SessionStore({
    host: 'localhost' ,
    port: 3306 ,
    user: 'root' ,
    password: 'root' ,
    database: 'session' ,
    useConnectionPooling: true 
});

[Solved] PostgreSQL enumeration type usage error: operator does not exist error handling 

//Creating Enumeration Classes
CREATE TYPE USER_ROLE AS ENUM ('MALE', 'FEMALE');
//Add conversion rules
CREATE CAST (VARCHAR AS USER_ROLE) WITH INOUT AS IMPLICIT;
//Create table, add fields of enumeration type
create table sys_user
(
    row_id      bigserial          not null
        constraint sys_user_pkey primary key,
    create_time timestamp(6),
    update_time timestamp(6),
    del_flag    smallint default 0 not null,
    role        USER_ROLE      not null,
    user_name   varchar(200)       not null
);

Because the conversion rule is added, you can directly use the varchar type string as the judgment condition query in pgadmin, but if you use mybatis to query the database, the error operator does not exist will be reported

select * from sys_user where del_flag = 0 and role = 'MALE'

Solution: convert varchar type to enumeration type and compare

Method 1
select * from sys_user where del_flag = 0 and role = cast(#{role} as user_role)；
Method 2
select * from sys_user where del_flag = 0 and role = #{role}::user_role;

[Solved] MYSQL Error: unknown error 1130, unknown error 1045

When using Navicat to link mysql, the following error is reported:

Solution:

Log in to MySQL on the server and enter use MySQL:

root@localhost 09:07:  [mysql]> update user set host = '%' where user = 'root';
Query OK, 1 row affected (0.07 sec)
root@localhost 09:12:  [mysql]> flush privileges;
Query OK, 0 rows affected (0.02 sec)

Then, using the Navicat link again, the following appears:

Solution:

GRANT ALL PRIVILEGES ON *.* TO ‘root’@’%’ IDENTIFIED BY ‘yourpassword’ WITH GRANT OPTION

root@localhost 09:13:  [mysql]> GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY 'yourpassword' WITH GRANT OPTION;
Query OK, 0 rows affected, 1 warning (0.02 sec)

root@localhost 09:14:  [mysql]> flush privileges;
Query OK, 0 rows affected (0.02 sec)

To sum up: this kind of error is probably caused by the permissions set by the root user in MySQL in the database

[Solved Perfectly] MySQL ERROR 1064 (42000): You have an error in your SQL syntax;

The perfect solution to error 1064

1064 error code appears when setting the root account password in MySQL

at first, I thought the user name and password could not be the same, so I changed it to 123456

and found it still couldn’t.

Solution

Enter as follows:

alter user 'root'@localhost identified by '123456';

By ‘…’ is followed by the new password.