Suzanne B. Shu and Kurt A. Carlson have a paper (pdf) on this claim:

How many positive claims should be used to produce the most positive impression of a product or service? This article posits that in settings where consumers know that the message source has a persuasion motive, the optimal number of positive claims is three. More claims are better until the fourth claim, at which time consumers’ persuasion knowledge causes them to see all the claims with skepticism. The studies in this paper establish and explore this pattern, which is referred to as the charm of three. An initial experiment finds that impressions peak at three claims for sources with persuasion motives but not for sources without a persuasion motive. Experiment 2 finds that this occurs for attitudes and impressions, and that increases in skepticism after three claims explain the effect. Two final experiments examine the process by investigating how cognitive load and sequential claims impact the effect.

Here is a NYT summary of those results.

Frustrated San Francisco drivers who are fed up having to circle around trying find a parking space on the street can use a new app that allows them to purchase a spot from someone who is already parked in one.

The app, called ‘Monkey Parking,’ connects drivers looking for empty spaces with someone who is also on the app who is willing to give up their prized spot, but for a fee of anywhere between $5 and $20.

That article is here, and there is another here.

For pointers I thank John Thorne and Mark Thorson and Daniel Kent.

Meanwhile, here is markets in everything at Newport Beach High School, namely paying for higher “draft picks” for the prom…via George Pearkes.

Speaking of California, here is Virginia Postrel on overindividuation in Mother’s Day gift giving.

The MySQL client has some functionalities some of us never use. Why would you use them and what is the added value of this?

Every DBA and developer has had a moment when he or she needs to connect to a MySQL database using the command line tool. Therefore I’ve written down an explanation of some command line commands you can insert in the CLI, most of them give added value and make your experience with the cli more enjoyable.

prompt

Who has never witnessed the scary feeling of not being connected to the write database when having several terminals open. I do, due to the fact I use the prompt functionality.

mysql >\R Production >
PROMPT set to 'Production > '

Or you can go a bit further and visualise the user, host and active database in:

mysql > \R \u@\h [\d]>
PROMPT set to '\u@\h [\d]>'
root@testbox [test]>

edit

In some situations editing the query in an editor instead of the cli can have several enhancements. It gives you the ability to fix typos, have a deep look at the queries before you submit them and etc.
If you’d like to edit the query you are making in your default editor instead of using the cli.

mysql> \e

The editor appears, in which you can create your query/ies.

use sakila;
select * from city
limit 10;
~
~
~

After closing this down and putting a delimiter in the cli, this query will be run against the database while outputting in the prompt.

mysql> \e
-> ;
+---------+--------------------+------------+---------------------+
| city_id | city               | country_id | last_update         |
+---------+--------------------+------------+---------------------+
|       1 | A Corua (La Corua) |         87 | 2006-02-15 04:45:25 |
|       2 | Abha               |         82 | 2006-02-15 04:45:25 |
|       3 | Abu Dhabi          |        101 | 2006-02-15 04:45:25 |
|       4 | Acua               |         60 | 2006-02-15 04:45:25 |
|       5 | Adana              |         97 | 2006-02-15 04:45:25 |
|       6 | Addis Abeba        |         31 | 2006-02-15 04:45:25 |
|       7 | Aden               |        107 | 2006-02-15 04:45:25 |
|       8 | Adoni              |         44 | 2006-02-15 04:45:25 |
|       9 | Ahmadnagar         |         44 | 2006-02-15 04:45:25 |
|      10 | Akishima           |         50 | 2006-02-15 04:45:25 |
+---------+--------------------+------------+---------------------+
10 rows in set (0.03 sec)

tee

Performing critical maintenance on a database could require to have an entire log of performed queries and actions. You can activate the full output of the MySQL client, including your performed queries. This utility is ideal if you prefer having a log of all of your actions. This could be for documentation stakes or a way to reread your actions if issues would occur.

Example:

mysql> \T /tmp/tee.log
Logging to file '/tmp/tee.log'

This will provide in the output the queries you perform.

dim0@testing101:~$ cat /tmp/tee.log
mysql> select * from city limit 5;
+---------+--------------------+------------+---------------------+
| city_id | city               | country_id | last_update         |
+---------+--------------------+------------+---------------------+
|       1 | A Corua (La Corua) |         87 | 2006-02-15 04:45:25 |
|       2 | Abha               |         82 | 2006-02-15 04:45:25 |
|       3 | Abu Dhabi          |        101 | 2006-02-15 04:45:25 |
|       4 | Acua               |         60 | 2006-02-15 04:45:25 |
|       5 | Adana              |         97 | 2006-02-15 04:45:25 |
+---------+--------------------+------------+---------------------+
5 rows in set (0.00 sec)

Whenever, you have only access to the MySQL interface and you need to access one of your created files to see what the output is, you can do so using the \! keystroke, which will execute system commands.
Running a shell command from the MySQL command line interface:

mysql> \! cat /tmp/tee.log
mysql> select * from city limit 5;
+---------+--------------------+------------+---------------------+
| city_id | city               | country_id | last_update         |
+---------+--------------------+------------+---------------------+
|       1 | A Corua (La Corua) |         87 | 2006-02-15 04:45:25 |
|       2 | Abha               |         82 | 2006-02-15 04:45:25 |
|       3 | Abu Dhabi          |        101 | 2006-02-15 04:45:25 |
|       4 | Acua               |         60 | 2006-02-15 04:45:25 |
|       5 | Adana              |         97 | 2006-02-15 04:45:25 |
+---------+--------------------+------------+---------------------+
5 rows in set (0.00 sec)

status

In some cases you’d like seeing the parameters currently active on your MySQL client. Therefore you can actually use the \s command. This command will clarify which of the options are active on the client. The info which is shown should not be confused with SHOW VARIABLES. which is focussed on the connection variables.
Trigger the status information of your connection using \s:

mysql> \s>
--------------
mysql  Ver 14.14 Distrib 5.6.15, for Linux (x86_64) using  EditLine wrapper
Connection id:		13149
Current database:	sakila
Current user:		root@localhost
SSL:			Not in use
Current pager:		stdout
Using outfile:		''
Using delimiter:	;
Server version:		5.6.15-63.0-log Percona Server (GPL), Release 63.0
Protocol version:	10
Connection:		127.0.0.1 via TCP/IP
Server characterset:	latin1
Db     characterset:	latin1
Client characterset:	utf8
Conn.  characterset:	utf8
TCP port:		3306
Uptime:			10 days 23 hours 32 min 57 sec
Threads: 1  Questions: 1203169  Slow queries: 43745  Opens: 626  Flush tables: 1  Open tables: 178  Queries per second avg: 1.268
--------------

clear

Clearing your current input query. Use \c to clear the input field:

mysql> SELECT *
-> FROM city
-> \c
mysql>

pager

Honestly one of the more useful tools in the mysqlclient is actually pager. For people prone to typing queries while forgetting adding a limit if they don’t need to view the full output.
‘\P less’ will output the query data using the UNIX command less.
You can also choose to output the query results in a parsable format on the filesystem using ‘\P cat > voila.log’.

for example:

mysql> \P cat > /tmp/voila.log
PAGER set to 'cat > /tmp/voila.log'
mysql> SELECT *  FROM city;
600 rows in set (0.01 sec)

This will create the file ‘voila.log’ in which only the output is saved of the query. This solution mimics the ‘SELECT INTO OUTFILE’ query.

During optimisation of your workload, it can be interesting to see if a query you’ve modified has the same query output

mysql >\P md5sum
PAGER set to 'md5sum'
 root@127.0.0.1 [sakila]>select * from city limit 10;
449d5bcae6e0e5b19e7101478934a7e6  -
10 rows in set (0.00 sec)
 mysql >select city_id, city, country_id, last_update FROM city LIMIT 10 ;
449d5bcae6e0e5b19e7101478934a7e6  -
10 rows in set (0.00 sec)

Other commands

There are of course several other options you might use. You can get an overview of all the internal cli functions through \?.

Disabling the tee and pager commands described in this blogentry can be done with \t or notee, \n or \nopager.

The post DBA 101: Sometimes forgotten functionality in the MySQL client appeared first on MySQL Performance Blog.

Via Mark Perry:

In a ground-breaking technology move for the automotive industry, Volvo Cars demonstrates the world’s first delivery of food to the car – a new form of ‘roam delivery’ services. The service will allow consumers to have their shopping delivered straight to their car, no matter where they are. Volvo’s new digital keys technology means that car owners will be able to choose their car as a delivery option when ordering goods online. Via a smartphone or a tablet, the owner will be informed when a delivery company wants to drop off or pick up something from the car.

Having accepted the delivery, he or she then hands out a digital key and can track when the car is opened and then locked again. Once the pick-up or drop-off is completed, the digital key ceases to exist.

For the pointer I thank Samir Varma.

I knew gas in Venezuela was underpriced, but I had not known by how much.  Nick Miroff brings us the latest:

Venezuela sits atop the world’s largest oil reserves, and its government sets the price of premium gasoline at about 5 cents a gallon. Its real price — adjusted to the soaring street value of the U.S. dollar — is half a penny per gallon.

But rest assured, there will be a move toward international prices:

The projected price hike is likely to push gas closer to 17 cents a gallon, at unofficial exchange rates.

There is more here.