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joplin notion extension/Web Development/sql/mysql.md
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joplin notion extension/Web Development/sql/mysql.md
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- MariaDB
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https://www.mariadbtutorial.com/getting-started/connect-to-mariadb/
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After installing mariaDB use this command to setup database directory
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`mariadb-install-db --user=mysql --basedir=/usr --datadir=/var/lib/mysql`
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do this `rm -rf /var/lib/mysql/*` to undo this initialization process
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To start mariadbd at boot time you have to copy
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**support-files/mariadb.service** to the right place for your system
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U can do this in systemd init system with
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`systemctl enable --now mariadb.service`
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Two all-privilege accounts were created.
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One is **root@localhost**, it has no password, but you need to
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be system 'root' user to connect. Use, for example, `sudo mysql`
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The second is **mysql@localhost**, it has no password either, but
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you need to be the system 'mysql' user to connect.
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After connecting you can set the password, if you would need to be
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able to connect as any of these users with a password and without sudo
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See the MariaDB Knowledgebase at https://mariadb.com/kb
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You can start the MariaDB daemon with:
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`cd '/usr' ; /usr/bin/mariadb-safe --datadir='/var/lib/mysql'`
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You can test the MariaDB daemon with mariadb-test-run.pl
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`cd '/usr/mariadb-test' ; perl mariadb-test-run.pl`
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Please report any problems at https://mariadb.org/jira
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The latest information about MariaDB is available at https://mariadb.org/.
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Consider joining MariaDB's strong and vibrant community:
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https://mariadb.org/get-involved/
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- More
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To load mysql shell in command prompt:
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`mysql -u root -p`
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Here root is owner_name. This will prompt for password which is ‘password’.
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or
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`mysql -h localhost -P 3306 -u root -p test`
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- To connect to remote mysql
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To connect to MariaDB on a specific host, you use the -h option:
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`mysql -u [username] -p[password] -h [hostname]`
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or to disable ssl check when connecting
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`mysql --skip-ssl -u proj1_wishrocky -P 3306 -p94db734d1935c57ac05eab8987a959c98f074706 -h r77rn.h.filess.io proj1_wishrocky`
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or (for newer versions)
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` mysql --ssl-mode=DISABLED -u proj1_wishrocky -P 3306 -p94db734d1935c57ac05eab8987a959c98f074706 -h r77rn.h.filess.io proj1_wishrocky`
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To get list of database:
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`show databases;`
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To create database
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```sql
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drop database if exists database_name;
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create database database_name;
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```
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To load database
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`use hospitals;`
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hospitals here is name of database
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Once database is loaded, to get list of tables:
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`show tables;`
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To get schema of tables:
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`desc patients;` or `describe patients;`
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where patients is name of table
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- To create table
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```sql
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drop table if exists table_name;
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create table table_name(....);
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```
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- Creating table
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```sql
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create table project (
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emp_id int not null,
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id int not null,
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name varchar(30),
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location varchar(40),
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primary key(emp_id)
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);
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```
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- Adding Auto increment
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- SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE.
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```sql
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-- To let the AUTO_INCREMENT sequence start with another value, use the following SQL statement:
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ALTER TABLE Persons AUTO_INCREMENT=100;
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alter table employee
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modify emp_id int not null auto_increment;
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```
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- Change mysql password if forget
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- Stop mysql service
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`sudo systemctl stop mysql`
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- start it in safe mode
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`sudo mysqld_safe --skip-grant-tables --skip-networking`
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- Then in other terminal type
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`mysql -u root`
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- when in mysql shell
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`FLUSH PRIVILEGES;`
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`ALTER USER 'root'@'localhost' IDENTIFIED BY 'new_password';`
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- close the terminal of the safe mode and start mysql service again
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`sudo systemctl start mysql`
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- running sql script in mysql
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`mysql -u username -p`
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then
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`SOURCE /path/to/your/script.sql;`
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Alternatively, you can execute the script directly from the command line without entering the MySQL shell
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`mysql -u username -p < /path/to/your/script.sql`
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- if else use in mysql
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```sql
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SET @primaryKeyValue = 13; /* Your primary key value here */
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IF EXISTS (SELECT 1 FROM TableB WHERE foreignKeyColumn = @primaryKeyValue) THEN
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-- Update the record in TableA
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UPDATE TableA
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SET someField = 'newValue' -- Set your field and value accordingly
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WHERE primaryKeyColumn = @primaryKeyValue;
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ELSE
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-- Delete the record in TableA
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DELETE FROM TableA
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WHERE primaryKeyColumn = @primaryKeyValue;
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END IF;
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```
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- creating and using procedures
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```sql
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-- to replace semicolon with // for procedures
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DELIMITER //
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CREATE PROCEDURE if not EXISTS UpdateOrDeleteQuestion(IN primaryKeyValue INT)
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BEGIN
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IF EXISTS (SELECT 1 FROM quiz_questions WHERE questionID = primaryKeyValue) THEN
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-- Update the record in questions
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UPDATE questions
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SET isDeleted = TRUE
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WHERE id = primaryKeyValue;
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ELSE
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-- Delete the record in questions
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DELETE FROM questions
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WHERE id = primaryKeyValue;
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END IF;
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END //
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DELIMITER ;
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-- Now you can call the procedure with the primary key value
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CALL UpdateOrDeleteQuestion(2);
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-- to delete it
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drop procedure UpdateOrDeleteQuestion;
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```
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- to run mysql in docker first setup `/var/lib/mysql` by
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`mysql_install_db --user=root --basedir=/usr --datadir=/var/lib/mysql`
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then
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```bash
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mysqld_safe --user=root &
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# Wait for MySQL to initialize (this is important)
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sleep 5
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# other scripts to start (like backend services)
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# npm start
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```
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in order to check if mysql is listening on localhost:3306 try this
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`netstat -tuln | grep 3306`
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|id|username|discriminator|avatar|accent_color|banner|theme_colors|pronouns|phone|desktop|mobile|premium|premium_type|bot|bio|system|nsfw_allowed|mfa_enabled|totp_secret|totp_last_ticket|created_at|premium_since|verified|disabled|deleted|email|flags|public_flags|purchased_flags|premium_usage_flags|rights|data|fingerprints|settingsIndex|webauthn_enabled|badge_ids|avatar_decoration_data|display_name_styles|collectibles|primary_guild|
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|--|--------|-------------|------|------------|------|------------|--------|-----|-------|------|-------|------------|---|---|------|------------|-----------|-----------|----------------|----------|-------------|--------|--------|-------|-----|-----|------------|---------------|-------------------|------|----|------------|-------------|----------------|---------|----------------------|-------------------|------------|-------------|
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