MySQL Command Reference

Combine 2 fields into one result

SELECT CONCAT(fieldname1, fieldname2) FROM table

Example:

SELECT CONCAT(u.first, ' ', u.last) AS name FROM usr_table u

 ID |    first |      last |
-----------------------------
  1 |    Led   |      Hed  |
  2 |    Jimmy |      Page |

Results:

 Name
-----------          
Led Hed
Jimmy Page

Add fixed String to a field

SELECT CONCAT(fieldname1, 'fixed string') FROM table

Do not return Duplicates

SELECT DISTINCT fieldname FROM table

Return the 'Sum' of all fields selected

SELECT SUM(fieldname) FROM table

Round to 2 decimal places

SELECT ROUND(fieldname, 2) FROM table

Selects only the field with the highest numerical value

SELECT MAX(fieldname) FROM table

Selects the leftmost 4 characters in a field

SELECT LEFT(fieldname, 4) FROM table

Select date and format result in MM/DD/YYYY

SELECT DATE_FORMAT(fieldname, '%c/%d/%Y') from table

%a 	Abbreviated weekday name (Sun..Sat)
%b 	Abbreviated month name (Jan..Dec)
%c 	Month, numeric (0..12)
%D 	Day of the month with English suffix (0th, 1st, 2nd, 3rd, …)
%d 	Day of the month, numeric (00..31)
%e 	Day of the month, numeric (0..31)
%f 	Microseconds (000000..999999)
%H 	Hour (00..23)
%h 	Hour (01..12)
%I 	Hour (01..12)
%i 	Minutes, numeric (00..59)
%j 	Day of year (001..366)
%k 	Hour (0..23)
%l 	Hour (1..12)
%M 	Month name (January..December)
%m 	Month, numeric (00..12)
%p 	AM or PM
%r 	Time, 12-hour (hh:mm:ss followed by AM or PM)
%S 	Seconds (00..59)
%s 	Seconds (00..59)
%T 	Time, 24-hour (hh:mm:ss)
%U 	Week (00..53), where Sunday is the first day of the week
%u 	Week (00..53), where Monday is the first day of the week
%V 	Week (01..53), where Sunday is the first day of the week; used with %X
%v 	Week (01..53), where Monday is the first day of the week; used with %x
%W 	Weekday name (Sunday..Saturday)
%w 	Day of the week (0=Sunday..6=Saturday)
%X 	Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V
%x 	Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v
%Y 	Year, numeric, four digits
%y 	Year, numeric (two digits)
%% 	A literal ‘%’ character
%x 	x, for any ‘x’ not listed above

Join fields from different tables

SELECT a.fieldname1 b.fieldname2 FROM tableA a LEFT JOIN tableB b ON a.fieldname1 = b.fieldname1

To join these fields the values of a.fieldname1 and b.fieldname1 must be equal
Example: SELECT j.JobName b.Amount FROM job j JOIN invoice i ON j.JobID = i.JobID WHERE j.JobID = '00123'
The job table and invoice table were joined by the value of their JobID fields
b.Amount was Selected from the invoice table where invoice.JobID = '00123' and j.JobName was Selected from the job table where job.JobID = '00123'

Change Column order within a table

Reference: http://dev.mysql.com/doc/refman/5.0/en/change-column-order.html

ALTER TABLE TableName MODIFY COLUMN ColumnNameToMove longtext AFTER ColumnNameToPutAfter
ALTER TABLE TableName MODIFY COLUMN ColumnNameToMove longtext BEFORE ColumnNameToPutBefore
ALTER TABLE TableName MODIFY COLUMN ColumnNameToMove longtext FIRST

Allow access from remote host

GRANT ALL ON <DatabaseName>.* TO <User>@"<IP Address or Hostname>" IDENTIFIED BY "<Password>";
FLUSH PRIVILEGES;

Example:

GRANT ALL ON *.* TO root@"10.0.0.25" IDENTIFIED BY "SomePassword";
FLUSH PRIVILEGES;

This grants 'ALL' privileges for every database (*.*) to the user 'root' when connecting from IP Address 10.0.0.25 and the password given is 'SomePassword'
NOTE: Granting 'ALL' privileges to all (*.*) databases can be a security risk. In real world scenarios, only grant the privileges that are necessary and only to the user/hosts that need them.

Show a Triggers

SHOW TRIGGERS;

Delete a Trigger

DROP TRIGGER <Trigger_Name>;

Show Database Size

SELECT table_schema AS "Database", 
ROUND(SUM(data_length + index_length) / 1024 / 1024, 2) AS "Size (MB)" 
FROM information_schema.TABLES 
GROUP BY table_schema;

Show Table Size

SELECT table_schema as "Database", table_name AS "Table", 
ROUND(((data_length + index_length) / 1024 / 1024), 2) "Size in MB" 
FROM information_schema.TABLES 
ORDER BY (data_length + index_length) DESC;