Essential MySQL Queries

1. Create a quick backup

Before testing a new piece of code you suspect might mess up data in one or more tables it's always a good practice to create a backup. To quickly create a backup copy of a table, use this query:

CREATE TABLE backup SELECT * FROM TABLE original;

The query creates a table backup which is a copy of the original table and includes both structure and content. 2. Create/change/restore a password

Many applications store MD5-crypted passwords in the database. If you want to quickly create a new MD5-ed password, or you have forgotten your password, use the following query to get a new one:

SELECT MD5('somepasshere');

This statement will give you "b5bab206cc8002bf7c10d47b24a2d0e6" which is the encrypted version of the string "somepasshere". There are other function that crypt stings in MySQL using different algorithms, most notably

PASSWORD()

which is using MySQL's own crypting algorithm. 3. Working with Unix timestamps

To convert from human-readable MySQL date/time format into Unix timestamp, use:

SELECT UNIX_TIMESTAMP(); 

Without parameters, this will give you the timestamp of the current date and time. With parameters, you can get timestamp for any date. For example:

SELECT UNIX_TIMESTAMP('2006-12-31');

This statement gives you the timestamp 1167541200. To get a date back from a timestamp, use:

SELECT FROM_UNIXTIME(1167541200); 

This results in "2006-12-31 00:00:00" 4. Quick increment

To increment an integer stored in a table (useful for stats for example), use:

UPDATE sometable SET counter=counter+1 WHERE …;

Here "counter" is the name of the field that stores the integer value. 5. Toggle a value

If you have a field that stores a Boolean type of value, like 0/1 or yes/no, you can easily toggle the value with one if-statement:

UPDATE sometable SET flag=(IF(flag='no','yes','no'));

6. Find/replace

Say you want to update a piece of text if all records in a table field. REPLACE() comes to the rescue:

UPDATE sometable SET field = REPLACE(field, 'black','white');

This statement will replace all occurrences of the string "black" with the string "white" in all records of the "field" column. Apart from the string "white" the rest of the text contained in the field will be left as is. 7. Get a random record

If you want to select a random row in your table, you can use the statement:

SELECT * FROM table ORDER BY RAND();

8. Upper/lower case

If you want to modify a value and make it upper or lowercase, use the UPPER or LOWER functions, like this:

SELECT LOWER("Value"); // gives you "value"

SELECT UPPER("Value"); // gives you "VALUE"