MySQL Cheat Sheet Rumi, February 1, 2012 Selecting a database: mysql> USE database; Listing databases: mysql> SHOW DATABASES; Listing tables in a db: mysql> SHOW TABLES; Describing the format of a table: mysql> DESCRIBE table; Creating a database: mysql> CREATE DATABASE db_name; Creating a table: mysql> CREATE TABLE table_name (field1_name TYPE(SIZE), field2_name TYPE(SIZE)); Ex: mysql> CREATE TABLE pet (name VARCHAR(20), sex CHAR(1), birth DATE); Load tab-delimited data into a table: mysql> LOAD DATA LOCAL INFILE "infile.txt" INTO TABLE table_name; (Use \n for NULL) Inserting one row at a time: mysql> INSERT INTO table_name VALUES ('MyName', 'MyOwner', '2002-08-31'); (Use NULL for NULL) Retrieving information (general): mysql> SELECT from_columns FROM table WHERE conditions; All values: SELECT * FROM table; Some values: SELECT * FROM table WHERE rec_name = "value"; Multiple critera: SELECT * FROM TABLE WHERE rec1 = "value1" AND rec2 = "value2"; Reloading a new data set into existing table: mysql> SET AUTOCOMMIT=1; # used for quick recreation of table mysql> DELETE FROM pet; mysql> LOAD DATA LOCAL INFILE "infile.txt" INTO TABLE table; Fixing all records with a certain value: mysql> UPDATE table SET column_name = "new_value" WHERE record_name = "value"; Selecting specific columns: mysql> SELECT column_name FROM table; Retrieving unique output records: mysql> SELECT DISTINCT column_name FROM table; Sorting: mysql> SELECT col1, col2 FROM table ORDER BY col2; Backwards: SELECT col1, col2 FROM table ORDER BY col2 DESC; Date calculations: mysql> SELECT CURRENT_DATE, (YEAR(CURRENT_DATE)-YEAR(date_col)) AS time_diff [FROM table]; MONTH(some_date) extracts the month value and DAYOFMONTH() extracts day. Pattern Matching: mysql> SELECT * FROM table WHERE rec LIKE "blah%"; (% is wildcard – arbitrary # of chars) Find 5-char values: SELECT * FROM table WHERE rec like "_____"; (_ is any single character) Extended Regular Expression Matching: mysql> SELECT * FROM table WHERE rec RLIKE "^b$"; (. for char, […] for char class, * for 0 or more instances ^ for beginning, {n} for repeat n times, and $ for end) (RLIKE or REGEXP) To force case-sensitivity, use "REGEXP BINARY" Counting Rows: mysql> SELECT COUNT(*) FROM table; Grouping with Counting: mysql> SELECT owner, COUNT(*) FROM table GROUP BY owner; (GROUP BY groups together all records for each 'owner') Selecting from multiple tables: (Example) mysql> SELECT pet.name, comment FROM pet, event WHERE pet.name = event.name; (You can join a table to itself to compare by using 'AS') Currently selected database: mysql> SELECT DATABASE(); Maximum value: mysql> SELECT MAX(col_name) AS label FROM table; Auto-incrementing rows: mysql> CREATE TABLE table (number INT NOT NULL AUTO_INCREMENT, name CHAR(10) NOT NULL); mysql> INSERT INTO table (name) VALUES ("tom"),("dick"),("harry"); Adding a column to an already-created table: mysql> ALTER TABLE tbl ADD COLUMN [column_create syntax] AFTER col_name; Removing a column: mysql> ALTER TABLE tbl DROP COLUMN col; (Full ALTER TABLE syntax available at mysql.com.) Batch mode (feeding in a script): # mysql -u user -p < batch_file (Use -t for nice table layout and -vvv for command echoing.) Alternatively: mysql> source batch_file; Backing up a database with mysqldump: # mysqldump –opt -u username -p database > database_backup.sql (Use 'mysqldump –opt –all-databases > all_backup.sql' to backup everything.) (More info at MySQL's docs.) Related MySQL MySQL
Perfect way to reset MySQL Root Password on Debian/Ubuntu August 9, 2016 If you forgot your MySQL root password, you can reset it by following these steps. 1. Stop the MySQL service. service mysql stop 2. Start MySQL without password and permission checks. mysqld_safe –skip-grant-tables & 3. Press [ENTER] again if your output is halted. 4. Connect to MySQL. mysql -u root… Read More
MySQL Replication June 27, 2011 MySQL is the relational database system of choice for open sourcers. Replication is the process of replicating data from one MySQL database server (the master) into another (the slave). We’ll go into why you would want to replicate a MySQL database in another article. MySQL Replication Using the master-slave configuration… Read More
Reset a MySQL root password for Debian July 14, 2016 Use the following steps to reset a MySQL root password by using the command line interface. Stop the MySQL service (Ubuntu and Debian) Run the following command: sudo /etc/init.d/mysql stop (CentOS, Fedora, and Red Hat Enterprise Linux) Run the following command: sudo /etc/init.d/mysqld stop Start MySQL without a password Run… Read More