Archive for July, 2012
Delay or synchronize it?
A couple students in one of my classes ran into a problem when competing Java threads tried to insert new rows in a table. They raised an error when they tried the DELAY keyword to avoid the race (collision) condition in an INSERT statement. It was simple to explain to them that the DELAY keyword doesn’t work with an InnoDB table. Any attempt throws the following error:
ERROR 1616 (HY000): DELAYED OPTION NOT supported FOR TABLE 'message' |
Important Update: INSERT DELAYED is gone in MySQL 5.6.6 (announcement) and the whole issue comes down to synchronizing threads (some dislike the solution) or using the ON DUPLICATE KEY clause.
They retested their Java application after redefining the target table using the MyISAM engine. They found it worked but that’s a bad fix in Java (a brief Java/MySQL tutorial post). They really needed to synchronize the Java thread (line #22), leave out the DELAY keyword, and manage the table with the InnoDB engine. Here’s the modified Java code (by the way, they named their project VulcanTech if you’re wondering about the packages in the import statement):
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | package vulcantech.vth.server.commands; import java.io.IOException; import java.net.Socket; import vulcantech.vth.server.combeans.MessageBean; public class MessageHandler implements Handler { @Override public void handleIt(Object... args) { MessageBean message = (MessageBean) args[0]; Socket sock = (Socket) args[1]; DatabaseConnection dbconnection = new DatabaseConnection(); String update = new String("INSERT INTO message(message_timestamp, sender, recipient, message, checked) VALUES(\'" + message.getTimeStamp() + "\', \'" + message.getSender() + "\', \'" + message.getRecipient() + "\', \'" + message.getMessage() + "\', b\'0\')"); synchronized (this) { dbconnection.executeUpdate(update); } try { sock.getOutputStream().write(1); } catch (IOException e) { e.printStackTrace(); } dbconnection.close(); } } |
Hope this helps those who encounter race conditions against MySQL when you’re writing Enterprise Java Beans (EJBs).
PHP for MySQL Striped View
Back in May I explained how to create MySQL striped views with session variables. A couple folks wanted to know how to implement them through PHP programs. The trick is sharing the same connection between a call to the function before a query against the striped view.
I’ve updated the MySQL example beyond the Hobbit analogy from the prior post. It now uses the following database components:
- An
APPLICATION_USERtable - A striped
AUTHORIZED_USERview - A
FUNCTION_QUERYview to optimize function calls - A
SET_LOGINfunction - A
GET_LOGIN_ID function - A
GET_USER_IDfunction
The definition of the APPLICATION_USER table is:
CREATE TABLE application_user ( user_id int(10) unsigned PRIMARY KEY AUTO_INCREMENT , user_name varchar(20) NOT NULL , user_role varchar(20) NOT NULL , user_group_id int(10) unsigned NOT NULL , user_type int(10) unsigned NOT NULL , first_name varchar(20) , middle_name varchar(20) , last_name varchar(20) , created_by int(10) unsigned NOT NULL , creation_date datetime NOT NULL , last_updated_by int(10) unsigned NOT NULL , last_update_date datetime NOT NULL , CONSTRAINT natural_key UNIQUE (user_name) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1; |
You should note that the natural key is a user-defined user name (mind you in reality it is often set by the application administrator). This guarantees that the authorize_cursor in the set_login function below always returns only one row.
The following seeds five rows in the APPLICATION_USER table:
INSERT INTO application_user VALUES ( null, 'potterhj', 'System Admin', 2, 1, 'Harry', 'James', 'Potter', 1, NOW(), 1, NOW()) ,( null, 'weasilyr', 'Guest', 1, 1, 'Ronald', null, 'Weasily', 1, NOW(), 1, NOW()) ,( null, 'longbottomn', 'Guest', 1, 1, 'Neville', null, 'Longbottom', 1, NOW(), 1, NOW()) ,( null, 'holmess', 'DBA', 3, 1, 'Sherlock', null, 'Holmes', 1, NOW(), 1, NOW()) ,( null, 'watsonj', 'DBA', 3, 1, 'John', 'H', 'Watson', 1, NOW(), 1, NOW()); |
Before creating the striped view, you should create the functions that set the session variables and query them. The set_login function sets two session variables when successful, which requires a user name that matches a valid value in the user_name column of the application_user table. The function returns an integer of 1 on success and 0 on failure. The set_login function code follows.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | CREATE FUNCTION set_login(pv_login_name VARCHAR(20)) RETURNS INT UNSIGNED BEGIN /* Declare a local variable to verify completion of the task: || ========================================================== || a. Default value is zero, which means false. || b. Non-default value is one, which means true. || ========================================================== */ DECLARE lv_success_flag INT UNSIGNED DEFAULT 0; /* Declare local variables to hold the return values from the cursor. */ DECLARE lv_login_id INT UNSIGNED; DECLARE lv_group_id INT UNSIGNED; /* Declare a condition variable for zero rows fetched, selected, or processed. */ DECLARE no_rows_fetched CONDITION FOR 1329; /* Declare a cursor to return an authorized user id. */ DECLARE authorize_cursor CURSOR FOR SELECT a.user_id , a.user_group_id FROM application_user a WHERE a.user_name = pv_login_name; /* Declare a handler for the cursor when it fails to return a row. */ DECLARE EXIT HANDLER FOR no_rows_fetched BEGIN /* The return statement when the function is aborted through an error. */ RETURN lv_success_flag; END; /* Check whether the input value is something other than a null value. */ IF pv_login_name IS NOT NULL THEN OPEN authorize_cursor; FETCH authorize_cursor INTO lv_login_id, lv_group_id; CLOSE authorize_cursor; /* Set the success flag. */ SET @sv_login_id := lv_login_id; SET @sv_group_id := lv_group_id; /* Check whether the session variables are set. */ IF NOT ISNULL(@sv_login_id) AND @sv_login_id > 0 AND NOT ISNULL(@sv_group_id) AND @sv_group_id > 0 THEN SET lv_success_flag := 1; END IF; END IF; /* Return the success flag. */ RETURN lv_success_flag; END; $$ |
The following GET_LOGIN_ID function returns the value from the @sv_login_id variable.
1 2 3 4 5 6 | CREATE FUNCTION get_login_id() RETURNS INT UNSIGNED BEGIN /* Return the success flag. */ RETURN @sv_login_id; END; $$ |
The following GET_GROUP_ID function returns the value from the @sv_group_id variable.
1 2 3 4 5 6 | CREATE FUNCTION get_group_id() RETURNS INT UNSIGNED BEGIN /* Return the success flag. */ RETURN @sv_group_id; END; $$ |
Lastly, you create the MySQL striped AUTHORIZED_USER like this one. It looks ineffective because it includes four function calls to the get_group_id() and one to the get_login_id().
CREATE VIEW authorized_user AS SELECT au.user_id , au.user_name , au.user_role , CONCAT(au.last_name,", ",au.first_name," ",IFNULL(au.middle_name,"")) AS full_name FROM application_user au WHERE (au.user_group_id = 1 AND au.user_group_id = get_group_id() AND au.user_id = get_login_id()) OR get_group_id() = 2 OR (get_group_id() > 2 AND au.user_group_id = get_group_id()); |
The prior view’s query lets you see the logic for the three types of access. You can eliminate the multiple function calls by using an inline view, like the following in a SQL statement:
CREATE VIEW authorized_user AS SELECT au.user_id , au.user_name , au.user_role , CONCAT(au.last_name,", ",au.first_name," ",IFNULL(au.middle_name,"")) AS full_name FROM application_user au CROSS JOIN (SELECT get_login_id() AS login_id , get_group_id() AS group_id) fq WHERE (au.user_group_id = 1 AND au.user_group_id = fq.group_id AND au.user_id = fq.login_id) OR fq.group_id = 2 OR (fq.group_id > 2 AND au.user_group_id = fq.group_id); |
Unfortunately, the preceding query raises the following exception if you attempt to put it in a view:
ERROR 1349 (HY000): View's SELECT contains a subquery in the FROM clause |
MySQL raises the error because a SELECT statement can’t contain a subquery in the FROM clause, according to the Create View MySQL Reference material.
The solution to the limitation of the CREATE VIEW syntax requires that you breakup the SQL statement into queries, and put them into separate views. The following example shows the function_query view holding the function calls and the authorized_user view cross joining the function_query view.
CREATE VIEW function_query AS SELECT get_login_id() AS login_id , get_group_id() AS group_id; CREATE VIEW authorized_user AS SELECT au.user_id , au.user_name , au.user_role , CONCAT(au.last_name,", ",au.first_name," ",IFNULL(au.middle_name,"")) AS full_name FROM application_user au CROSS JOIN function_query fq WHERE (au.user_group_id = 1 AND au.user_group_id = fq.group_id AND au.user_id = fq.login_id) OR fq.group_id = 2 OR (fq.group_id > 2 AND au.user_group_id = fq.group_id); |
The following PHP program calls the SET_LOGIN function before querying the AUTHORIZED_USER view. It uses a $_GET global parameter to simplify testing the concept but you should always run parameters through the $_POST global parameter. The $_GET and $_REQUEST global parameters are security risks.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 | <html>
<header>
<title>Static Query Object Sample</title>
<style type="text/css">
/* HTML element styles. */
table {background:white;border-style:solid;border-width:3px;border-color:black;border-collapse:collapse;}
th {text-align:center;font-style:bold;background:lightgray;border:solid 1px gray;}
td {border:solid 1px gray;}
/* Class tag element styles. */
.ID {min-width:50px;text-align:right;}
.Label {min-width:200px;text-align:left;}
</style>
</header>
<body>
<?php
// Process the input parameter, which should be through a $_POST argument.
(isset($_GET['user_name'])) ? $input = $_GET['user_name'] : $input = '';
// Assign credentials to connection.
$mysqli = new mysqli("localhost", "student", "student", "studentdb");
// Check for connection error and print message.
if ($mysqli->connect_errno) {
print $mysqli->connect_error."<br />";
print "Connection not established ...<br />";
}
else {
// Declare a dynamic function call.
$query = "SELECT set_login(?)";
// Attempt preparing statement.
if (!$stmt = $mysqli->prepare($query)) {
// Print failure to resolve query message.
print $mysqli->error."<br />";
print "Failed to resolve query ...<br />";
}
else {
// Bind variable to SQL statement and execute it.
$stmt->bind_param("s", $input);
$stmt->execute();
$stmt->close();
}
// Declare a static query.
$query = "SELECT au.user_id, au.user_name, au.user_role, au.full_name FROM authorized_user au" ;
// Loop through a result set until completed.
do {
// Attempt query and exit with failure before processing.
if (!$stmt = $mysqli->query($query)) {
// Print failure to resolve query message.
print $mysqli->error."<br />";
print "Failed to resolve query ...<br />";
}
else {
// Print the opening HTML table tag.
print '<table><tr><th class="ID">ID</th><th class="Label">User Name</th><th class="Label">User Role</th><th class="Label">Full Name</th></tr>';
// Fetch a row for processing.
while( $row = $stmt->fetch_row() ) {
// Print the opening HTML row tag.
print "<tr>";
// Loop through the row's columns.
for ($i = 0;$i < $mysqli->field_count;$i++) {
// Handle column one differently.
if ($i == 0)
print '<td class="ID">'.$row[$i]."</td>";
else
print '<td class="Label">'.$row[$i]."</td>";
}
// Print the closing HTML row tag.
print "</tr>";
}
}
} while( $mysqli->next_result());
// Print the closing HTML table tag.
print "</table>";
// Release connection resource.
$mysqli->close(); }
?>
</script>
</body>
</html> |
You can call this through a browser with the following type of URL. You have two possible striped values, and they are any user’s unique user name.
http://localhost/stripedquery1.php?user_name=potterhj |
It returns one row when the user isn’t in a privileged group, all rows when the user is the root privileged group and all rows for a privilege group when not in the root privileged group. Naturally, you can extend this level of individual and group membership.
You can test this in the web page or directly in MySQL. The MySQL test doesn’t require image files and thereby loads faster, which is why I’ve opted to show it to you that way.
- Test for the root privilege group:
SELECT set_login('potterhj'); |
You get the full five rows:
+---------+-------------+--------------+----------------------+ | user_id | user_name | user_role | full_name | +---------+-------------+--------------+----------------------+ | 1 | potterhj | System Admin | Potter, Harry James | | 2 | weasilyr | Guest | Weasily, Ronald | | 3 | longbottomn | Guest | Longbottom, Neville | | 4 | holmess | DBA | Sherlock, Holmes | | 5 | watsonj | DBA | John, Watson H | +---------+-------------+--------------+----------------------+ |
- Test for an individual in a non-privileged group:
SELECT set_login('weasilyr'); |
You get the single user’s row:
+---------+-----------+-----------+------------------+ | user_id | user_name | user_role | full_name | +---------+-----------+-----------+------------------+ | 2 | weasilyr | Guest | Weasily, Ronald | +---------+-----------+-----------+------------------+ |
- Test for a non-root privileged group:
SELECT set_login('holmess'); |
You get the two rows that belong to the non-root privileged group:
+---------+-----------+-----------+-------------------+ | user_id | user_name | user_role | full_name | +---------+-----------+-----------+-------------------+ | 4 | holmess | DBA | Holmes, Sherlock | | 5 | watsonj | DBA | Watson, John H | +---------+-----------+-----------+-------------------+ |
Naturally, it’s more effective to put these components into a function library. The trick to making this work in a session is to share the connection. The object approach to the MySQL Improved (mysqli) object holds the connection, and that’s whats passed in the following example files.
This is an optimistic setter function. It forks (starts) the MySQL SQL/PSM set_login function but it doesn’t wait see if it ran successfully. That’s the nature of optimistic programming solutions, and the principal problem with them.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | function set_login($mysqli, $user_name) { // Define return string. $return = false; // Declare a dynamic function call. $query = "SELECT set_login(?)"; // Attempt preparing statement. if (!$stmt = $mysqli->prepare($query)) { // Print failure to resolve query message. print $mysqli->error."<br />"; print "Failed to resolve query ...<br />"; } else { // Bind variable to SQL statement and execute it. $stmt->bind_param("s", $user_name); $stmt->execute(); $stmt->close(); $return = true; } // Return the string. return $return; } |
An optimistic setter function fails to synchronize behaviors between the PHP and MySQL coding levels. It should be rewritten to fork the MySQL SQL/PSM set_login function and evaluate it’s successful or unsuccessful completion, which makes it a pessimistic function.
There are two ways to solve this problem. One can write a wrapper that accesses the get_login_id stored function to confirm the session variable is set, and the other handles the return value from the native set_login_id stored function. The former requires knowledge of the internal workings of the database model, while the latter does not. That means the first is more tightly coupled than the latter.
The following set_login PHP function is rewritten to be pessimistic but dependent on a supplemental call to another get_login PHP function, which calls the get_login_id stored function in the MySQL Server:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | function set_login($mysqli, $user_name) { // Define return string. $return = false; // Declare a dynamic function call. $query = "SELECT set_login(?)"; // Attempt preparing statement. if (!$stmt = $mysqli->prepare($query)) { // Print failure to resolve query message. print $mysqli->error."<br />"; print "Failed to resolve query ...<br />"; } else { // Bind variable to SQL statement and execute it. $stmt->bind_param("s", $user_name); $stmt->execute(); $stmt->close(); // True only when query returns a row. if (get_login($mysqli)) { $return = true; } } // Return the string. return $return; } |
A more effective solution reads the return value from the set_login function, like this:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | function set_login($mysqli, $user_name) { // Define return string. $return = false; // Declare a dynamic function call. $query = "SELECT set_login(?)"; // Attempt preparing statement. if (!$stmt = $mysqli->prepare($query)) { // Print failure to resolve query message. print $mysqli->error."<br />"; print "Failed to resolve query ...<br />"; } else { // Bind variable to SQL statement and execute it. $stmt->bind_param("s", $user_name); // Attempt query and exit with failure before processing. if (!$stmt->execute()) { // Print failure to resolve query message. print $mysqli->error."<br />"; print "Failed to resolve query ...<br />"; } else { // Fetch a row for processing. $result = $stmt->get_result(); $row = $result->fetch_array(MYSQLI_NUM); } // Close the statement cursor. $stmt->close(); // True only when query returns a row. if (!is_null($row[0]) && ($row[0] > 0)) { $return = true; } } // Return the string. return $return; } |
This is the getter function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | function get_login($mysqli) { // Define return string. $return = false; // Declare a dynamic function call. $query = "SELECT get_login_id()"; // Attempt preparing statement. if (!$stmt = $mysqli->query($query)) { // Print failure to resolve query message. print $mysqli->error."<br />"; print "Failed to resolve query ...<br />"; } else { // Fetch a SQL statement. $row = $stmt->fetch_row(); // Close the statement. $stmt->close(); // True only when query returns a row. if (!is_null($row[0]) && ($row[0] > 0)) { $return = true; } } // Return the string. return $return; } |
The get_authorized_user PHP function gets and displays the table result from the authorized_user striped view:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 | function get_authorized_user($mysqli) { // Define return string. $out = ''; // Declare a static query. $query = "SELECT au.user_id, au.user_name, au.user_role, au.full_name FROM authorized_user au" ; // Loop through a result set until completed. do { // Attempt query and exit with failure before processing. if (!$stmt = $mysqli->query($query)) { // Print failure to resolve query message. print $mysqli->error."<br />"; print "Failed to resolve query ...<br />"; } else { // Print the opening HTML table tag. $out .= '<table><tr><th class="ID">ID</th><th class="Label">User Name</th>' . '<th class="Label">User Role</th><th class="Label">Full Name</th></tr>'; // Fetch a row for processing. while( $row = $stmt->fetch_row() ) { // Print the opening HTML row tag. $out .= "<tr>"; // Loop through the row's columns. for ($i = 0;$i < $mysqli->field_count;$i++) { // Handle column one differently. if ($i == 0) $out .= '<td class="ID">'.$row[$i]."</td>"; else $out .= '<td class="Label">'.$row[$i]."</td>"; } // Print the closing HTML row tag. $out .= "</tr>"; } } } while( $mysqli->next_result()); // Print the closing HTML table tag. $out .= "</table>"; // Return an HTML table of the results. return $out; } |
This is the modified program using the functions:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 | <style type="text/css">
/* HTML element styles. */
table {background:white;border-style:solid;border-width:3px;border-color:black;border-collapse:collapse;}
th {text-align:center;font-style:bold;background:lightgray;border:solid 1px gray;}
td {border:solid 1px gray;}
/* Class tag element styles. */
.ID {min-width:50px;text-align:right;}
.Label {min-width:200px;text-align:left;}
</style>
</header>
<body>
<?php
// Include the credentials file if omitted.
include_once("striping.inc");
// Process the input parameter, which should be through a $_POST argument.
(isset($_GET['user_name'])) ? $input = $_GET['user_name'] : $input = '';
// Assign credentials to connection.
$mysqli = new mysqli("localhost", "student", "student", "studentdb");
// Check for connection error and print message.
if ($mysqli->connect_errno) {
print $mysqli->connect_error."<br />";
print "Connection not established ...<br />";
}
else {
// After setting the session variable, get the striped view result.
if (set_login($mysqli,$input)) {
// Print the authorized list.
print get_authorized_user($mysqli);
}
// Release connection resource.
$mysqli->close();
}
?>
</script>
</body>
</html> |
Hope this helps those implementing MySQL Striped tables.
Free Oracle PHP Book
Six years ago, I wrote Oracle Database 10g Express Edition PHP Web Programming for the release of the express edition. It was a lot of fun to write because I enjoy the PHP programming language, but unfortunately sales didn’t measure up too well. That’s probably because the population of PHP developers working with Oracle was small.
Today it seems there are more PHP developers working with Oracle 11g. While the population of PHP community for Oracle 11g is still smaller than for MySQL, it continues to grow year-over-year.
The FREE Underground PHP and Oracle Manual can help those converting PHP to run in the Oracle Call Interface, which is the replacement for MySQLi Interface. Chris Jones (an Oracle Open Source Product Manager) and Alison Holloway (an Oracle Senior Product Manager) write and maintain this book. It’s a great place to start if you’re migrating to Oracle Database 11g from MySQL.
PHP/MySQL Query
Somebody wanted an example of how to handle column values using PHP to query a MySQL database. While I thought there were enough examples out there, they couldn’t find one that was code complete.
Well, here’s one that works using a static query. If you want to use a prepared statement, check this earlier post.
<html>
<header>
<title>Static Query Object Sample</title>
<style type="text/css">
/* HTML element styles. */
table {background:white;border-style:solid;border-width:3px;border-color:black;border-collapse:collapse;}
th {text-align:center;font-style:bold;background:lightgray;border:solid 1px gray;}
td {border:solid 1px gray;}
/* Class tag element styles. */
.ID {min-width:50px;text-align:right;}
.Label {min-width:200px;text-align:left;}
</style>
</header>
<body>
<?php
// Assign credentials to connection.
$mysqli = new mysqli("localhost", "student", "student", "studentdb");
// Check for connection error and print message.
if ($mysqli->connect_errno) {
print $mysqli->connect_error."<br />";
print "Connection not established ...<br />";
}
else {
// Declare a static query.
$query = "SELECT au.system_user_id, au.system_user_name FROM system_user au" ;
// Loop through a result set until completed.
do {
// Attempt query and exit with failure before processing.
if (!$stmt = $mysqli->query($query)) {
// Print failure to resolve query message.
print $mysqli->error."<br />";
print "Failed to resolve query ...<br />";
}
else {
// Print the opening HTML table tag.
print '<table><tr><th class="ID">ID</th><th class="Label">User Role Name</th></tr>';
// Fetch a row for processing.
while( $row = $stmt->fetch_row() ) {
// Print the opening HTML row tag.
print "<tr>";
// Loop through the row's columns.
for ($i = 0;$i < $mysqli->field_count;$i++) {
// Handle column one differently.
if ($i == 0)
print '<td class="ID">'.$row[$i]."</td>";
else
print '<td class="Label">'.$row[$i]."</td>";
}
// Print the closing HTML row tag.
print "</tr>";
}
}
} while( $mysqli->next_result());
// Print the closing HTML table tag.
print "</table>";
// Release connection resource.
$mysqli->close(); }
?>
</script>
</body>
</html> |
It prints the following image:
While you shouldn’t embed CSS, I’ve done it to keep this as simple as possible. You can also use the procedural approach to the MySQLi library, like this:
<html>
<header>
<title>Static Query Procedural Sample</title>
<style type="text/css">
/* HTML element styles. */
table {background:white;border-style:solid;border-width:3px;border-color:black;border-collapse:collapse;}
th {text-align:center;font-style:bold;background:lightgray;border:solid 1px gray;}
td {border:solid 1px gray;}
/* Class tag element styles. */
.ID {min-width:50px;text-align:right;}
.Label {min-width:200px;text-align:left;}
</style>
</header>
<body>
<?php
// Assign credentials to connection.
$mysqli = mysqli_connect("localhost", "student", "student", "studentdb");
// Check for connection error and print message.
if (mysqli_connect_errno()) {
print mysqli_connect_error()."<br />";
print "Connection not established ...<br />";
}
else {
// Initialize a statement in the scope of the connection.
$stmt = mysqli_stmt_init($mysqli);
// Declare a static query.
$query = "SELECT au.system_user_id, au.system_user_name FROM system_user au" ;
// Loop through a result set until completed.
do {
// Attempt query and exit with failure before processing.
if (!$stmt = mysqli_query($mysqli,$query)) {
// Print failure to resolve query message.
print mysqli_error($stmt)."<br />";
print "Failed to resolve query ...<br />";
}
else {
// Print the opening HTML table tag.
print '<table><tr><th class="ID">ID</th><th class="Label">User Role Name</th></tr>';
// Fetch a row for processing.
while( $row = mysqli_fetch_row($stmt) ) {
// Print the opening HTML row tag.
print "<tr>";
// Loop through the row's columns.
for ($i = 0;$i < mysqli_field_count($mysqli);$i++) {
// Handle column one differently.
if ($i == 0)
print '<td class="ID">'.$row[$i]."</td>";
else
print '<td class="Label">'.$row[$i]."</td>";
}
// Print the closing HTML row tag.
print "</tr>";
}
}
} while( mysqli_next_result($mysqli));
// Print the closing HTML table tag.
print "</table>";
// Free system resources.
mysqli_stmt_free_result($stmt);
// Release connection resource.
mysqli_close($mysqli);
}
?>
</script>
</body>
</html> |
It produces the same output as the object oriented approach with one exception the title of the web page.
Hope this helps some folks.
Placement over substance
I was stunned when a SQL query raised an ERROR 1630 (42000) telling me the SUM function didn’t exist in MySQL 5.5.23. The fix was simple. The opening parenthesis of the SUM function must be on the same line as the SUM keyword without an intervening white space. Alternatively phrased, you can’t have a line return or white space between the SUM function name and the opening parenthesis of the call parameter list. The same rule doesn’t apply to the opening parenthesis of the FORMAT function and it seems to me that this parsing inconsistency is problematic.
Therefore, my surprise, observation, and complaint is that all functions don’t parse the same way, using the same rules. That is, unless you use specialized SQL_MODE settings. This assumption was borne out by Kolbe Kegel’s comment on this post, and there are 30 remaining built in functions that have specialized parsing and resolution markers.
A simplified version of the code that raises the error follows. As you’ll notice the opening parenthesis for the FORMAT and SUM function have intervening white space and a line return.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | SELECT t.transaction_account AS "Transaction" , LPAD(FORMAT (SUM (CASE WHEN EXTRACT(MONTH FROM transaction_date) = 1 AND EXTRACT(YEAR FROM transaction_date) = 2011 THEN CASE WHEN t.transaction_type = cl.common_lookup_type THEN t.transaction_amount ELSE t.transaction_amount * -1 END END),2),10,' ') AS "JAN" FROM TRANSACTION t CROSS JOIN common_lookup cl WHERE cl.common_lookup_table = 'TRANSACTION' AND cl.common_lookup_column = 'TRANSACTION_TYPE' AND cl.common_lookup_type = 'DEBIT' GROUP BY t.transaction_account; |
Based on the comments, the SQL_MODE is:
mysql> SELECT @@version, @@sql_mode; +-----------+----------------------------------------------------------------+ | @@version | @@sql_mode | +-----------+----------------------------------------------------------------+ | 5.5.23 | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | +-----------+----------------------------------------------------------------+ 1 ROW IN SET (0.00 sec) |
It raises the following error:
ERROR 1630 (42000): FUNCTION studentdb.SUM does NOT exist. CHECK the 'Function Name Parsing and Resolution' SECTION IN the Reference Manual |
Moving ONLY the opening parenthesis to the end of the SUM keyword (or removing the line return and white space from between the SUM keyword and opening parenthesis) prevents the error but it would be more convenient if it supported both approaches. It seems odd that an intervening line return and white space for the SUM function raises an exception while the same intervening line return and white space doesn’t raise an exception for the FORMAT function. It strikes me the parser should support both or reject both. Here’s the fixed code that works without enabling the IGNORE_SPACE SQL Mode option.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | SELECT t.transaction_account AS "Transaction" , LPAD(FORMAT (SUM( CASE WHEN EXTRACT(MONTH FROM transaction_date) = 1 AND EXTRACT(YEAR FROM transaction_date) = 2011 THEN CASE WHEN t.transaction_type = cl.common_lookup_type THEN t.transaction_amount ELSE t.transaction_amount * -1 END END),2),10,' ') AS "JAN" FROM TRANSACTION t CROSS JOIN common_lookup cl WHERE cl.common_lookup_table = 'TRANSACTION' AND cl.common_lookup_column = 'TRANSACTION_TYPE' AND cl.common_lookup_type = 'DEBIT' GROUP BY t.transaction_account; |
As noted by the comments, adding the IGNORE_SPACE to the SQL_MODE lets both queries work without moving the open parenthesis. You can do that in a session with the following syntax (which is covered in an older post):
SET SQL_MODE=(SELECT CONCAT(@@sql_mode,',IGNORE_SPACE')); |
Hope this helps folks…
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