what is the speed hit of "SELECT *" with MySql, as opposed to narrower database calls?


Are there any benchmarks on how much an extra, unneeded VARCHAR, CHAR,
INT, BIGINT, TEXT or MEDIUMTEXT slows down a database call with MySql?
PostGre info would also be useful.

I'm trying to explain to some friends the utility of making database
calls return only needed data.

As an example of what I'm talking about, suppose we had a database
table sort of like this:

table weblogs (
int id,
varchar 255 headline,
text mainContent,
int dateCreated,
varchar 255 author,
varchar 255 navigationText,
char 1 isPrivate
);


Suppose I'm doing a PHP command that get's the headlines and offers a
link to the actual page. What is the speed difference between

SELECT * FROM weblogs

as opposed to

SELECT id, headline FROM weblogs

And is there info out there that gives a general sense of how much each
extra, unneeded database field might slow down a script?

.

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