MySQL

What does mysql return when the selection doesnt exist?

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Join Date: Jan 2009

Posts: 103

Reputation: jakx12 is an unknown quantity at this point

Solved Threads: 4

jakx12

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What does mysql return when the selection doesnt exist?

Nov 4th, 2009

Ok so what does mysql return when the select query doesnt exist. So say I query the database: SELECT username FROM user WHERE username='test' AND password='test'

Ok so say test doesnt exist what will the database return because i code in java and have made a method that should return true or false. True if the the thing exists in the query and false if it doesnt. But for some reason it always returns true. It turns out because mysql returns something each time.

Thanks

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Join Date: Nov 2007

Posts: 3,761

Reputation: nav33n is a jewel in the rough

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nav33n

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Nov 5th, 2009

Hi, I am not sure how you are validating what mysql returns. In php, when you query the table, for example,

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 MySQL Syntax (Toggle Plain Text) 
//query the table with username AND password 
$query = "select * from table where username='test' and password='test'";
//execute the query AND save the resource IN $result. 
$result = mysql_query($query);
//If the variable $result IS TRUE AND if the query RETURNS more than 0 rows, (meaning, there IS a record!) THEN display convenient message.
if(mysql_num_rows($result) > 0) {
 echo "Username and password exists!";
} ELSE {
//ELSE, no records exist
 echo "No records found.";
}
//query the table with username and password 
$query = "select * from table where username='test' and password='test'";
//execute the query and save the resource in $result. 
$result = mysql_query($query);
//If the variable $result is true and if the query returns more than 0 rows, (meaning, there is a record!) then display convenient message.
if(mysql_num_rows($result) > 0) {
 echo "Username and password exists!";
} else {
//else, no records exist
 echo "No records found.";
}

In php however, this will return false if a record doesn't exist in the table. If it has a record, then it will return all the columns of that record as a resource.
I am not sure about Java, but I think mysql will return an empty result set if no records are found.

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