Hi all,
How do I check in a mySQL table called 'Users' on column user_name when
registering a new user_name to make sure the new 'user_name' does not
already exist in that column?
TIA
18  1759 
>How do I check in a mySQL table called 'Users' on column user_name when registering a new user_name to make sure the new 'user_name' does not
already exist in that column?
An appropriate way is to insert a row with the username, and it will
fail if the username is in use because of the unique index you have
on the user_name column.
Gordon L. Burditt
*** Domestos wrote/escribió (Mon, 13 Jun 2005 20:50:51 GMT): How do I check in a mySQL table called 'Users' on column user_name when
registering a new user_name to make sure the new 'user_name' does not
already exist in that column?
I normally do something like this:
SELECT id FROM users WHERE username='john'
If zero rows are returned, the username is available.
--
-- Álvaro G. Vicario - Burgos, Spain
-- http://bits.demogracia.com - Mi sitio sobre programación web
-- Don't e-mail me your questions, post them to the group
--
Alvaro G Vicario пишет: *** Domestos wrote/escribió (Mon, 13 Jun 2005 20:50:51 GMT):
How do I check in a mySQL table called 'Users' on column user_name when
registering a new user_name to make sure the new 'user_name' does not
already exist in that column?
I normally do something like this:
SELECT id FROM users WHERE username='john'
If zero rows are returned, the username is available.
I guess better use not ='john' but like 'john', because of case-sensitive
Domestos wrote: Hi all,
How do I check in a mySQL table called 'Users' on column user_name when
registering a new user_name to make sure the new 'user_name' does not
already exist in that column?
TIA
The database can do this by implementing a unique constraint on the column
user_name. After issuing the INSERT, (or any SQL command), check for an
error, and report it. This then solves your general problem of enforcing
data integrity and reporting errors.
--
Kenneth Downs
Secure Data Software, Inc.
(Ken)nneth@(Sec )ure(Dat)a(.com )
Kenneth Downs пишет: Domestos wrote:
Hi all,
How do I check in a mySQL table called 'Users' on column user_name when
registering a new user_name to make sure the new 'user_name' does not
already exist in that column?
TIA
The database can do this by implementing a unique constraint on the column
user_name. After issuing the INSERT, (or any SQL command), check for an
error, and report it. This then solves your general problem of enforcing
data integrity and reporting errors.
checking for the SQL error is not a good idea, actually.
Well known programing prupose to use select before insert.
>> The database can do this by implementing a unique constraint on the column user_name. After issuing the INSERT, (or any SQL command), check for an
error, and report it. This then solves your general problem of enforcing
data integrity and reporting errors.
checking for the SQL error is not a good idea, actually.
Well known programing prupose to use select before insert.
This has the well-known problem that you may find the name not
in use, insert it, and find the name has been taken before you
got to it - unless you've gotten a lock first.
Gordon L. Burditt
Ivan Omelchenko 608308824 wrote: Kenneth Downs ?????: Domestos wrote:
Hi all,
How do I check in a mySQL table called 'Users' on column user_name when
registerin g a new user_name to make sure the new 'user_name' does not
already exist in that column?
TIA
The database can do this by implementing a unique constraint on the
column
user_name. After issuing the INSERT, (or any SQL command), check for an
error, and report it. This then solves your general problem of enforcing
data integrity and reporting errors.
checking for the SQL error is not a good idea, actually.
Well known programing prupose to use select before insert.
Well known on what planet?
The Server maintains integrity, that's why they were invented. This
protects the database against a buggy or intentionally misbehaving
application. Not surprisingly, it is also much faster.
--
Kenneth Downs
Secure Data Software, Inc.
(Ken)nneth@(Sec )ure(Dat)a(.com )
*** Gordon Burditt wrote/escribió (Tue, 14 Jun 2005 13:20:31 -0000): This has the well-known problem that you may find the name not
in use, insert it, and find the name has been taken before you
got to it - unless you've gotten a lock first.
If username field is defined as unique it shouldn't be a great issue. User
will get a generic error rather than a 'user not available' message. Not so
cute but, what's the probability of such a race condition if both queries
(SELECT and INSERT) and consecutive in your code?
--
-- Álvaro G. Vicario - Burgos, Spain
-- http://bits.demogracia.com - Mi sitio sobre programación web
-- Don't e-mail me your questions, post them to the group
--
>> This has the well-known problem that you may find the name not in use, insert it, and find the name has been taken before you
got to it - unless you've gotten a lock first.
If username field is defined as unique it shouldn't be a great issue. User
will get a generic error rather than a 'user not available' message. Not so
That assumes that you CHECK for errors on the insert, which "obviously"
can't happen since you already checked with SELECT, right? Wrong.
If you fail to check for errors on the insert, the user will think
he GOT the username he asked for, and then it won't work (since
presumably the password is different).
Queries ALWAYS take at least two moments and at least one query
from something else can always get in between them unless you've
done something to prevent that (e.g. locking, or ensuring that only
one client exists at a time).
Oh, yes, there's no reason why you have to give a "generic error"
if the insert fails, except, of course, for Bad Web Design(tm).
cute but, what's the probability of such a race condition if both queries
(SELECT and INSERT) and consecutive in your code?
If your site is popular enough, and lasts long enough, it's near
100% to happen eventually. And it will probably happen right when
your prospective client is about to decide to let you design his
web site at a generous rate, or when he's about to approve your
final check. Murphy's Law can be quite nasty.
The fact that you ask such a question means I don't want you any
where near the software design for airplanes, nuclear reactors, air
traffic control systems, weapons systems, automobile on-board
software, or cellular phone firmware. I don't really want you
around the design of any web sites I use to buy stuff, either.
Gordon L. Burditt This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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