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MySQL Cheatsheet

Permissions

Create Database:

mysql> CREATE DATABASE my_db;

Create User:

mysql> CREATE USER 'user1'@'%' IDENTIFIED BY 'securepass';

Grant User all Permissions to Database:

mysql> GRANT ALL PRIVILEGES ON my_db.* TO 'user1'@'%';

Grant User all Permissions to all databases with grant option:

mysql> GRANT ALL PRIVILEGES ON *.* TO 'user1'@'%' WITH GRANT OPTION;

Grant User all Permissions to Database in AWS RDS:

mysql> GRANT SELECT, UPDATE, DELETE, INSERT, CREATE, DROP, INDEX, ALTER, LOCK TABLES, EXECUTE, CREATE TEMPORARY TABLES, EXECUTE, TRIGGER, CREATE VIEW, SHOW VIEW, EVENT ON my_db.* TO user1@'%';

Update password:

mysql> UPDATE mysql.user SET authentication_string = PASSWORD('foobar') WHERE User = 'demo' and Host = '%';
# or
mysql> SET PASSWORD FOR 'demo'@'%' = PASSWORD('foobar');
# or
mysql> ALTER USER 'demo'@'%' IDENTIFIED BY 'foobar';
# or
mysql> ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';

Flush:

mysql> FLUSH PRIVILEGES;

Rename Users

RENAME USER 'john12' TO 'john.permanent';

Create Tables

Create a table:

mysql> CREATE TABLE domains (
  id INT(10) NOT NULL AUTO_INCREMENT,
  domain varchar(50) NOT NULL, 
  owner  varchar(50),
  year_registered int(4)
);

Create a table with primary key:

mysql> CREATE TABLE domains (
  id INT(10) NOT NULL AUTO_INCREMENT,
  domain varchar(50) NOT NULL, 
  owner  varchar(50),
  year_registered int(4),
  PRIMARY KEY (id) 
);

Create a table as a select query:

mysql> CREATE TABLE purchases_fnb_2016 
       AS 
         SELECT * FROM customers where date >= '2016-01-01 00:00:00' 
         AND date  <= '2016-10-29 00:00:00' 
         AND bank = 'fnb'
;

Create a table with a boolean data type:

CREATE TABLE myusers(name VARCHAR(50), matriculated BOOLEAN);

Insert with boolean data:

INSERT INTO myusers VALUES('tom', False);

Read data:

mysql> select name, matriculated from myusers limit 1;
+------+--------------+
| name | matriculated |
+------+--------------+
| tom  |            0 |
+------+--------------+

Use IF statement and replace value:

mysql> select name, IF(matriculated, 'yes', 'no') matriculated from myusers limit 1;
+------+--------------+
| name | matriculated |
+------+--------------+
| tom  | no           |
+------+--------------+

To query for people not matriculated:

mysql> select name, IF(matriculated, 'yes', 'no') matriculated from myusers where matriculated = false limit 1;
+------+--------------+
| name | matriculated |
+------+--------------+
| tom  | no           |
+------+--------------+

# you can use it without the if

To view unique values:

mysql> select distinct country from people;
+---------+
| country |
+---------+
| MOZ     |
| NGA     |
| KEN     |
| ZWE     |
| IND     |
| GHA     |
+---------+

To create a boolean column with default value of false:

CREATE TABLE users ( 
  active boolean not null default 0
);

To create a timestamp column:

CREATE TABLE users ( 
  time_created TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Then create a entry with now()

Changing Tables

Changing the column length:

mysql> ALTER TABLE contacts_business CHANGE COLUMN contact_number contact_number varchar(40);

Check and Repair Tables

Check all tables in mailscanner db:

$ mysqlcheck -c mailscanner -u root -p

Check all tables all dbs:

$ mysqlcheck -c  -u root -p --all-databases

Check one table:

$ check table maillog;

analyzes employee table that is located in thegeekstuff database:

$ mysqlcheck -a thegeekstuff employee -u root -p

optimizes employee table that is located in thegeekstuff database.

$ mysqlcheck -o thegeekstuff employee -u root -p

repairs employee table that is located in thegeekstuff database.

$ mysqlcheck -r thegeekstuff employee -u root -p

checks, optimizes and repairs all the corrupted table in thegeekstuff database.

$ mysqlcheck -u root -p --auto-repair -c -o thegeekstuff

optimize and repair all the tables across all your databases using the following command.

$ mysqlcheck -u root -p --auto-repair -c -o --all-databases

Delete

Delete data older than x:

mysql> delete from maillog where timestamp < "2012-09-07";
mysql> optimize table maillog;

Get Size in MB

SELECT table_schema "Data Base Name", 
sum( data_length + index_length ) / 1024 / 
1024 "Data Base Size in MB", 
sum( data_free )/ 1024 / 1024 "Free Space in MB" 
FROM information_schema.TABLES 
GROUP BY table_schema ;

View Logged in Users

SELECT SUBSTRING_INDEX(host, ':', 1) AS host_short, 
  GROUP_CONCAT(DISTINCT user) AS users, 
  COUNT(*) AS threads 
  FROM information_schema.processlist 
  GROUP BY host_short 
  ORDER BY COUNT(*), host_short;

Or:

SELECT `USER`, COUNT(*) FROM information_schema.processlist GROUP BY `USER`;

Indexes

Add a index to an existing table:

mysql> DESCRIBE salaries;
+-----------+---------+------+-----+---------+-------+
| Field     | Type    | Null | Key | Default | Extra |
+-----------+---------+------+-----+---------+-------+
| emp_no    | int(11) | NO   | PRI | NULL    |       |
| salary    | int(11) | NO   |     | NULL    |       |
| from_date | date    | NO   | PRI | NULL    |       |
| to_date   | date    | NO   |     | NULL    |       |
+-----------+---------+------+-----+---------+-------+
4 rows in set (0.00 sec)


ALTER TABLE salaries ADD INDEX ( salary );

Insert Data

Insert data into our domain table

mysql> INSERT INTO domains (domain,owner,year_registered) VALUES("example.com", "John", 2019);

Update Data

To update a students age and language where the student_id is something specific:

mysql> UPDATE students SET age = 30, language = 'english' WHERE student_id = 'fz9203493043';

Information Schema

Show me idle connections:

mysql> select id, user, host, db, command, time from information_schema.processlist where command = "sleep";
+-----------+-------+---------------------+--------+---------+------+
| id        | user  | host                | db     | command | time |
+-----------+-------+---------------------+--------+---------+------+
| 659558686 | james | 172.31.27.126:37154 | mydb12 | Sleep   |  332 |

Show me connected sessions:

mysql> select count(*) from information_schema.processlist;
+----------+
| count(*) |
+----------+
|       60 |
+----------+

or

mysql> show status where variable_name = 'threads_connected';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_connected | 61    |
+-------------------+-------+

Show connection related variables:

mysql> SHOW VARIABLES LIKE '%connections%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| extra_max_connections | 1     |
| max_connections       | 1296  |
| max_user_connections  | 0     |
+-----------------------+-------+
3 rows in set (0.16 sec)

or"

mysql> show status like '%onn%';
+-----------------------------------------------+-----------+
| Variable_name                                 | Value     |
+-----------------------------------------------+-----------+
| Aborted_connects                              | 35        |
| Connection_errors_accept                      | 0         |
| Connection_errors_internal                    | 0         |
| Connection_errors_max_connections             | 0         |
| Connection_errors_peer_address                | 0         |
| Connection_errors_select                      | 0         |
| Connection_errors_tcpwrap                     | 0         |
| Connections                                   | 66059     |
| Max_used_connections                          | 502       |
| Performance_schema_session_connect_attrs_lost | 0         |
| Slave_connections                             | 0         |
| Slaves_connected                              | 1         |
| Ssl_client_connects                           | 0         |
| Ssl_connect_renegotiates                      | 0         |
| Ssl_finished_connects                         | 0         |
| Threads_connected                             | 46        |
| wsrep_connected                               | OFF       |
+-----------------------------------------------+-----------+
17 rows in set (0.16 sec)

Show me cache information:

mysql> SHOW VARIABLES LIKE 'have_query_cache';
mysql> SHOW STATUS LIKE 'Qcache%';

Show me how long a connection can idle:

# https://aws.amazon.com/blogs/database/best-practices-for-configuring-parameters-for-amazon-rds-for-mysql-part-3-parameters-related-to-security-operational-manageability-and-connectivity-timeout/
mysql> SHOW VARIABLES LIKE 'wait_timeout';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| wait_timeout  | 28800 |
+---------------+-------+

Binlog format:

mysql> show variables like 'binlog_format';

Performance Schema Metrics:

Execution time of all the different statement types executed by each user:

mysql> select * from sys.user_summary_by_statement_type;
+------------+----------------+-------+---------------+-------------+--------------+-----------+---------------+---------------+------------+
| user       | statement      | total | total_latency | max_latency | lock_latency | rows_sent | rows_examined | rows_affected | full_scans |
+------------+----------------+-------+---------------+-------------+--------------+-----------+---------------+---------------+------------+
| background | select         |     1 | 212.00 us     | 212.00 us   | 0 ps         |         1 |             0 |             0 |          0 |
| root       | insert         |   175 | 46.26 s       | 823.43 ms   | 6.33 s       |         0 |             0 |       3919027 |          0 |
| root       | select         |    50 | 12.21 s       | 10.00 s     | 10.41 ms     |       223 |       7498268 |             0 |         17 |

Slowest statements (those in the 95th percentile by runtime):

mysql> select * from sys.statements_with_runtimes_in_95th_percentile\G
*************************** 1. row ***************************
            query: SELECT `sleep` (?)
               db: sys
        full_scan:
       exec_count: 1
        err_count: 0
       warn_count: 0
    total_latency: 10.00 s
      max_latency: 10.00 s
      avg_latency: 10.00 s
        rows_sent: 1
    rows_sent_avg: 1
    rows_examined: 0
rows_examined_avg: 0
       first_seen: 2019-07-04 11:21:23.155084
        last_seen: 2019-07-04 11:21:23.155084
           digest: x

Number of queries that generated errors or warnings:

mysql> SELECT SUM(errors) FROM sys.statements_with_errors_or_warnings;
+-------------+
| SUM(errors) |
+-------------+
|           4 |
+-------------+

Repair Table

mysql> repair table x;
mysql> optimize table x;

Scripting

Basic script to create the database and tables and using a for loop to insert data into mysql:

#!/usr/bin/env bash

user="root"
password="rootpassword"
database="my_db"

mysql -h 127.0.0.1 -u"$user" -p"$password" "$database" <<EOF
CREATE DATABASE IF NOT EXISTS foo;
CREATE TABLE IF NOT EXISTS foo.hashes (
  id INT AUTO_INCREMENT PRIMARY KEY,
  number INT(10) NOT NULL,
  hash VARCHAR(50) NOT NULL
);
EOF

for x in {1..10}
  do
    mysql -h 127.0.0.1 -u"$user" -p"$password" "$database" <<EOF
      INSERT IGNORE INTO foo.hashes (id, number, hash) VALUES ('', $x, "$(openssl rand -hex 8)");
    EOF
  done


mysql -h 127.0.0.1 -u"$user" -p"$password" "$database" <<EOF
  SELECT * FROM foo.hashes;
EOF

External Resources: