Web Development Exam > Web Development Videos > PHP for Absolute Beginners: From Novice to PHP Master > Beginner PHP Tutorial - 121 - More Basic Querying Part 2
Beginner PHP Tutorial - 121 - More Basic Querying Part 2 Video Lecture | PHP for Absolute Beginners: From Novice to PHP Master - Web Development
FAQs on Beginner PHP Tutorial - 121 - More Basic Querying Part 2 Video Lecture - PHP for Absolute Beginners: From Novice to PHP Master - Web Development
| 1. What is the purpose of the "mysqli_real_escape_string" function in PHP? |  |
Ans. The "mysqli_real_escape_string" function in PHP is used to escape special characters in a string before sending it as a query to the database. It helps prevent SQL injection attacks by ensuring that the query is properly formatted and any potentially harmful characters are handled correctly.
| 2. How can I retrieve data from a database using PHP and MySQL? | |
Ans. To retrieve data from a database using PHP and MySQL, you can use the "SELECT" statement in SQL. First, establish a connection to the database using the mysqli_connect() function. Then, execute the SELECT query using the mysqli_query() function, passing in the connection and the SQL statement. Finally, fetch the results using functions like mysqli_fetch_assoc() or mysqli_fetch_array() to retrieve the data from the query result.
| 3. Can I use variables in SQL queries with PHP? | |
Ans. Yes, you can use variables in SQL queries with PHP. To use variables in SQL queries, you can concatenate or interpolate them into the query string. For example, you can use the concatenation operator (".") to combine a variable value with the query string, or you can use double quotes and the variable name inside curly braces to interpolate the variable directly into the string.
| 4. How can I handle errors when executing database queries in PHP? | |
Ans. When executing database queries in PHP, you can use error handling techniques to catch and handle any potential errors. One approach is to use the "mysqli_error" function, which returns a string description of the last error that occurred during the execution of the query. You can check if the returned error string is empty or not to determine if an error occurred. Additionally, you can use try-catch blocks to catch exceptions thrown by the database functions and handle them accordingly.
| 5. Is it important to sanitize user input before using it in database queries? | |
Ans. Yes, it is crucial to sanitize user input before using it in database queries to prevent SQL injection attacks. Sanitizing user input involves removing or escaping special characters that could alter the meaning of the SQL query. One common method is to use prepared statements or parameterized queries, which separate the query logic from the user input, ensuring that the input is treated as data rather than executable code. Another approach is to use functions like "mysqli_real_escape_string" to escape special characters before using the input in the query.
Text Transcript from Video
now what it's done is it's returned my
first name in my surname because the
username and password were both found
and they both matched in the same row of
data so this will be classed as a
successful login so hopefully you
understand the concept of this and how
it could be used in PHP and we're going
to move on to some more queries now let
me just close this window let's browse
for the data let's start start from the
beginning so what happens if let's say
my surname changes okay
or let's say my first name changes it
could be anything so let's assume that
this user Alex with the password of
password wants to change the name of the
first name to Dale for example okay so
what I'm going to do is I'm going to
click SQL remember that the ID is 1 now
within PHP you have stored this
somewhere in a session if you've already
looked at sessions that like things like
login and you'll understand the idea of
the user could be stored in a session so
the current user so in PHP it's quite
easy once a users logged in and we've
said yet the user logged in is ID 1
we're referencing this user as ID 1
because it's a unique field we can
change anything just by reference being
back to this ID 1 and to do this we're
going to say we're not going to select
because we're not we're not returning
any data we're just changing what we
want to say is we want to say update
users set and then we choose the data we
want to set to different value
so set first-name equals Dale where
ID equals one so let's just go back to
this browse away from that new tab so
what we're doing here is we're updates
are using the update keyword and by the
way you don't have to do these in
capitals but what happens is if you
differentiate things like update and set
and we're in capitals you can see that
this is the difference between your
structured query language and what
you're actually dealing with so it's a
lot easier to see so what we're doing is
we're updating users so this is the
users table here what we're doing is
we're setting the first name equal to
Dale so the first name here equal to
Dale if you were to just say first name
equals Dale this would update both
surnames because we've not specified
what ID or what unique field you want to
set it by so set first-name equals Dale
where the ID equals one so what this is
going to do is it's going to select the
ID with Row one it's going to come
across and set the first name here to
Dale so let's just click on that I'll
click on go rather and you can see that
one row affected so it's telling us how
many rows have been affected and in this
case one rows good because we're
assuming that this is the row that we
want to update so now if we come into
browse let's just close that off you can
see that so you can see that we've
successfully updated this first name in
the table so you can start to begin to
see why this is useful for when we're
dealing with PHP for example a user
might want to change say their password
or they might want to change their first
name surname email address even anything
to do with that and we can do that
easily within our database obviously
we're not going to be working inside PHP
myadmin
we're going to be doing everything from
PHP which is slightly longer process but
it uses exactly the same queries and as
long as we've got this ID stored
somewhere in a session or a cookie then
we can work probably not gonna cook
excited be unsafe to some extent but if
it's stored somewhere then we would
would be able to do this so now let's
looking at now let's look at the
in rows so let's say I want to delete
this row here this art with IE 2 or even
ID 1 it doesn't really matter
so let's come into our SQL table again
and what we need to do is we need to
this time use the delete keyword we need
to say delete from and we need to
specify the table so users that's very
important delete from users where and
then all we need to do is specify the
column the preferably the unique column
so if we come back to here where ID
equals a certain amount you could say
where username equals Alex or where
password it called something but
obviously at the moment we're dealing
with sort of a user login type table so
we're going to delete we're you may use
ID equals 1 so it's just Y ID equals 1
so this is going to delete from users
where ID equals 1 so out just to mention
beforehand
we can use other comparison operators we
can say things like greater than or
equal to or each is equal to or just
greater than or less than and things
like that but obviously for now we're
just inning a single row so we're ID was
1
if we click go do you really want to
search giving us a confirmation message
because it knows that we're deleting we
can click OK it will say one row deleted
you'll give us how query back now what
we can do is we can just close this off
click on browse and you can see that
that row has been deleted so what
happens now if we want to reinsert a
whole new row of data we've already
looked at inserting the data manually
but from PHP we're going to want to say
create a user account we want to insert
the data and from scratch basically so
how are we going to do this we click on
insert only we don't we click on SQL
because we're doing it manually so I
want say insert into so it's pretty much
English language's it's easy to follow
because you can get it stuck inside your
head easy exactly what you're doing so
insert into obviously we're specifying
the table we want to set insight into so
insert into users then we use values and
we have two brackets
now inside here are the values we insert
corresponding to the fields so let's
just browse this now this is the
shorthand way of doing it and this is
what I'm going to be using you can do it
properly and long and specify each field
name as you go along but I'm just going
to be saying insert into users and then
I'm just going to put the values in here
they are in there going to be in a
single quotation marks separated by a
comma so at the moment if we have a look
we've got one two three four five
different fields so we need to insert
five different bits of data we've got 1
here 2 here 3 here 4 here and 5 here the
other way round to start 1 2 etc so the
comma separated values there we're using
single quotation marks now
ID can be left blank we know that
because we this is auto increment the
next value in set is going to have an ID
of 3 because we're coming from the last
value inserted 2 so we need to insert a
username and password a first name and a
surname so what we do is we insert say
Alex password Alex and Gavin now if we
don't specify say the last field here
we're going to be returned with an error
let's just have a look at that column
count doesn't match value at count value
count a right one now if you are ever
trying to insert data from PHP and you
are echoing out the sort of like results
of your query if you know you may have
an error and you get this this is
basically what what you need to focus on
you need to make sure that you're
inserting the data required if you don't
want to insert a surname for example you
still need to specify with these
inverted commas or rather single
quotation marks however you just you
can't leave it out so you have to insert
you know can be blank so I'm just going
to put Garrett in for now ok so that's
basically our simple query to insert
data so each of these we've comma
separated code
bond to our our column names our field
names so we've got ideas the first one
we've got user name as the second one
which is Alex then we've got the
password then we've got the first name
and the surname
okay so we've inserted them in order
where they correspond so let's click on
go you can see that one rows inserted
inserted row ID at 3 so now let's go and
click on browse and see what we've got
you can see that we've now reinserted
the value and/or the row with Alex
password Alex and Garrett and this is
now ID of 3 now what happens if I delete
all of these just simply using this
delete here and now what I want to do is
insert a new piece of data so I'm going
to go just insert anything
okay so we've inserted some data and now
you can see that it started ID 4
let's say we wanted to go back and we
want to start at ID 1 again now let's
just delete that you can use this tab
called omit in operations and if you
come down you can see auto increment we
can change this back to zero if we click
on go
first name in my surname because the
username and password were both found
and they both matched in the same row of
data so this will be classed as a
successful login so hopefully you
understand the concept of this and how
it could be used in PHP and we're going
to move on to some more queries now let
me just close this window let's browse
for the data let's start start from the
beginning so what happens if let's say
my surname changes okay
or let's say my first name changes it
could be anything so let's assume that
this user Alex with the password of
password wants to change the name of the
first name to Dale for example okay so
what I'm going to do is I'm going to
click SQL remember that the ID is 1 now
within PHP you have stored this
somewhere in a session if you've already
looked at sessions that like things like
login and you'll understand the idea of
the user could be stored in a session so
the current user so in PHP it's quite
easy once a users logged in and we've
said yet the user logged in is ID 1
we're referencing this user as ID 1
because it's a unique field we can
change anything just by reference being
back to this ID 1 and to do this we're
going to say we're not going to select
because we're not we're not returning
any data we're just changing what we
want to say is we want to say update
users set and then we choose the data we
want to set to different value
so set first-name equals Dale where
ID equals one so let's just go back to
this browse away from that new tab so
what we're doing here is we're updates
are using the update keyword and by the
way you don't have to do these in
capitals but what happens is if you
differentiate things like update and set
and we're in capitals you can see that
this is the difference between your
structured query language and what
you're actually dealing with so it's a
lot easier to see so what we're doing is
we're updating users so this is the
users table here what we're doing is
we're setting the first name equal to
Dale so the first name here equal to
Dale if you were to just say first name
equals Dale this would update both
surnames because we've not specified
what ID or what unique field you want to
set it by so set first-name equals Dale
where the ID equals one so what this is
going to do is it's going to select the
ID with Row one it's going to come
across and set the first name here to
Dale so let's just click on that I'll
click on go rather and you can see that
one row affected so it's telling us how
many rows have been affected and in this
case one rows good because we're
assuming that this is the row that we
want to update so now if we come into
browse let's just close that off you can
see that so you can see that we've
successfully updated this first name in
the table so you can start to begin to
see why this is useful for when we're
dealing with PHP for example a user
might want to change say their password
or they might want to change their first
name surname email address even anything
to do with that and we can do that
easily within our database obviously
we're not going to be working inside PHP
myadmin
we're going to be doing everything from
PHP which is slightly longer process but
it uses exactly the same queries and as
long as we've got this ID stored
somewhere in a session or a cookie then
we can work probably not gonna cook
excited be unsafe to some extent but if
it's stored somewhere then we would
would be able to do this so now let's
looking at now let's look at the
in rows so let's say I want to delete
this row here this art with IE 2 or even
ID 1 it doesn't really matter
so let's come into our SQL table again
and what we need to do is we need to
this time use the delete keyword we need
to say delete from and we need to
specify the table so users that's very
important delete from users where and
then all we need to do is specify the
column the preferably the unique column
so if we come back to here where ID
equals a certain amount you could say
where username equals Alex or where
password it called something but
obviously at the moment we're dealing
with sort of a user login type table so
we're going to delete we're you may use
ID equals 1 so it's just Y ID equals 1
so this is going to delete from users
where ID equals 1 so out just to mention
beforehand
we can use other comparison operators we
can say things like greater than or
equal to or each is equal to or just
greater than or less than and things
like that but obviously for now we're
just inning a single row so we're ID was
1
if we click go do you really want to
search giving us a confirmation message
because it knows that we're deleting we
can click OK it will say one row deleted
you'll give us how query back now what
we can do is we can just close this off
click on browse and you can see that
that row has been deleted so what
happens now if we want to reinsert a
whole new row of data we've already
looked at inserting the data manually
but from PHP we're going to want to say
create a user account we want to insert
the data and from scratch basically so
how are we going to do this we click on
insert only we don't we click on SQL
because we're doing it manually so I
want say insert into so it's pretty much
English language's it's easy to follow
because you can get it stuck inside your
head easy exactly what you're doing so
insert into obviously we're specifying
the table we want to set insight into so
insert into users then we use values and
we have two brackets
now inside here are the values we insert
corresponding to the fields so let's
just browse this now this is the
shorthand way of doing it and this is
what I'm going to be using you can do it
properly and long and specify each field
name as you go along but I'm just going
to be saying insert into users and then
I'm just going to put the values in here
they are in there going to be in a
single quotation marks separated by a
comma so at the moment if we have a look
we've got one two three four five
different fields so we need to insert
five different bits of data we've got 1
here 2 here 3 here 4 here and 5 here the
other way round to start 1 2 etc so the
comma separated values there we're using
single quotation marks now
ID can be left blank we know that
because we this is auto increment the
next value in set is going to have an ID
of 3 because we're coming from the last
value inserted 2 so we need to insert a
username and password a first name and a
surname so what we do is we insert say
Alex password Alex and Gavin now if we
don't specify say the last field here
we're going to be returned with an error
let's just have a look at that column
count doesn't match value at count value
count a right one now if you are ever
trying to insert data from PHP and you
are echoing out the sort of like results
of your query if you know you may have
an error and you get this this is
basically what what you need to focus on
you need to make sure that you're
inserting the data required if you don't
want to insert a surname for example you
still need to specify with these
inverted commas or rather single
quotation marks however you just you
can't leave it out so you have to insert
you know can be blank so I'm just going
to put Garrett in for now ok so that's
basically our simple query to insert
data so each of these we've comma
separated code
bond to our our column names our field
names so we've got ideas the first one
we've got user name as the second one
which is Alex then we've got the
password then we've got the first name
and the surname
okay so we've inserted them in order
where they correspond so let's click on
go you can see that one rows inserted
inserted row ID at 3 so now let's go and
click on browse and see what we've got
you can see that we've now reinserted
the value and/or the row with Alex
password Alex and Garrett and this is
now ID of 3 now what happens if I delete
all of these just simply using this
delete here and now what I want to do is
insert a new piece of data so I'm going
to go just insert anything
okay so we've inserted some data and now
you can see that it started ID 4
let's say we wanted to go back and we
want to start at ID 1 again now let's
just delete that you can use this tab
called omit in operations and if you
come down you can see auto increment we
can change this back to zero if we click
on go
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Nov 19, 2024 Last updated |
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