Archive for March, 2015
LAMP php-gd Libraries
Everything seemed complete after configuring my standalone MySQL instance to a LAMP installation, but last night I started playing with the image files. It turns out that I failed to install the php-gd library.
There’s very little feedback when you try to troubleshoot why you can’t read an image. In fact, the error message for reading the BLOB from MySQL was only available on the local Firefox browser:
The image "http://localhost/ConvertMySQLBlobToImage.php" cannot be displayed because it contains errors. |
The fix requires root to install the php-gd library with the yum utility:
yum install php-gd |
You’ll need to answer y to one question during the installation:
Loaded plugins: langpacks, refresh-packagekit mysql-connectors-community | 2.5 kB 00:00 mysql-tools-community | 2.5 kB 00:00 mysql56-community | 2.5 kB 00:00 pgdg93 | 3.6 kB 00:00 updates/20/x86_64/metalink | 16 kB 00:00 Resolving Dependencies --> Running transaction check ---> Package php-gd.x86_64 0:5.5.22-1.fc20 will be installed --> Processing Dependency: libt1.so.5()(64bit) for package: php-gd-5.5.22-1.fc20.x86_64 --> Running transaction check ---> Package t1lib.x86_64 0:5.1.2-14.fc20 will be installed --> Finished Dependency Resolution Dependencies Resolved ================================================================================ Package Arch Version Repository Size ================================================================================ Installing: php-gd x86_64 5.5.22-1.fc20 updates 89 k Installing for dependencies: t1lib x86_64 5.1.2-14.fc20 updates 164 k Transaction Summary ================================================================================ Install 1 Package (+1 Dependent package) Total download size: 252 k Installed size: 629 k Is this ok [y/d/N]: y Downloading packages: (1/2): php-gd-5.5.22-1.fc20.x86_64.rpm | 89 kB 00:00 (2/2): t1lib-5.1.2-14.fc20.x86_64.rpm | 164 kB 00:01 -------------------------------------------------------------------------------- Total 157 kB/s | 252 kB 00:01 Running transaction check Running transaction test Transaction test succeeded Running transaction (shutdown inhibited) Installing : t1lib-5.1.2-14.fc20.x86_64 1/2 Installing : php-gd-5.5.22-1.fc20.x86_64 2/2 Verifying : php-gd-5.5.22-1.fc20.x86_64 1/2 Verifying : t1lib-5.1.2-14.fc20.x86_64 2/2 Installed: php-gd.x86_64 0:5.5.22-1.fc20 Dependency Installed: t1lib.x86_64 0:5.1.2-14.fc20 Complete! |
After the installation, you can run the info.php program, which contains the following:
1 2 3 | <?php phpinfo(); ?> |
You’ll find the following gd library display in the result from the info.php program:
After retesting, we get both large text and blob files displayed in the web page:
As always, I hope this helps others. Especially, those who are working with your LAMP stack implementation of images.
MySQL bind-address
While I try to keep things simple, sometimes eliminating options and explanations comes back to haunt me. After posting how to open a Fedora firewall port for a LAMP stack, somebody got trapped by my instructions for installing MySQL on Fedora. They got stuck because they had the following setting in their /etc/my.cnf file:
bind-address=localhost.localdomain |
I’d suggested using that bind-address value for a DHCP VMware Fedora installation in Step #7. I was trying to create an example for an isolated testing instance, which is why I set the bind-address to a localhost.localdomain value. They raised the following error when they tried to connect their base operating system’s version of MySQL Workstation to the Fedora VM:
Failed to Connect to MySQL at 192.168.2.168:3306 with user student |
or, this dialog image:
Before you do the next step, please ensure you’re using the right IP address. You can find that by running this command as an authorized sudoer:
ifconfig | grep inet.*netmask.*broadcast |
In this case, the command returns:
inet 192.168.2.168 netmask 255.255.255.0 broadcast 192.168.2.255 |
I’ve since added instructions to the older post to set the bind-address value in the my.cnf file as follows when they want to support external connections (naturally that means authorizing port 3306):
bind-address=0.0.0.0 |
After you reset the /etc/my.cnf file, you must stop and start, or restart the mysqld service. You can do that as the root user like this:
systemctl restart mysqld |
Then, you can test a student user connection from MySQL Workbench like this:
If the student user is authorized and the password is correct, you’ll see that the connection now works:
As always, I hope this helps those working through similar issues.
Open Fedora Port 80
After installing the LAMP stack on Fedora, you need to open port 80 in the Firewall to access the PHP programs on the Fedora instance from external servers. You can open a firewall port by launching the firewall-config application as the root user with the following syntax:
firewall-config |
The firewall-config utility opens the following dialog:
Click on the Ports tab, and you’ll see the following:
Skip this step if you only want to set the runtime privilege to the port. Click on the Runtime tab and change it to Permanent if you want the port to be accessible when you reboot your OS.
Click on Add button to add a port exception, and you’ll see the following:
Enter Port 80 for the Apache server unless you used a different value for the Apache server’s listener port. If you’re not sure open the /etc/httpd/conf/httpd.conf file and check for the following line (default value shown):
Listen 80 |
Click the OK button to set the port exception. Then, you can connect to the Linux machine with the IP address, a DNS name, or a name you resolve in your local hosts file, like:
http://192.168.2.1/query.php |
You can find the IP address of your Fedora image by inspecting the /etc/hosts file or capture a DHCP assigned address with the following command as the root user (or with sudo as a valid sudoer user):
ifconfig -a |
It should return the following image, which is based on the data stored in MySQL’s studentdb database, as qualified in yesterday’s blog post:
I hope this helps those setting up a LAMP instance to work with the MySQL database.
Fedora Install LAMP
My students wanted an extra credit assignment, so I thought a LAMP configuration and test would be appropriate. The only problem was I hadn’t added it to their course VMware instance. So, here are the instructions to install Apache2, PHP, and MySQLi for a complete LAMP stack when MySQL is already installed.
The post builds on my Fedora Install of MySQL and MySQL Workbench on Fedora posts from last year. It also presumes that you’ve installed a studentdb database but you need to know how to do that let me know (but it hasn’t changed much from the example at the bottom of this old MySQL 5.1 blog post).
You install Apache2 with the following command as the root user, or with the sudo command as a sudoer-list user:
yum install httpd |
The following displays the results of starting the yum utility to install httpd, and you need to reply with a y to complete the installation:
Loaded plugins: langpacks, refresh-packagekit mysql-connectors-community | 2.5 kB 00:00 mysql-tools-community | 2.5 kB 00:00 mysql56-community | 2.5 kB 00:00 pgdg93 | 3.6 kB 00:00 updates/20/x86_64/metalink | 16 kB 00:00 updates | 4.9 kB 00:00 updates/20/x86_64/primary_db | 13 MB 00:04 (1/2): updates/20/x86_64/updateinfo | 1.9 MB 00:02 (2/2): updates/20/x86_64/pkgtags | 1.4 MB 00:01 Resolving Dependencies --> Running transaction check ---> Package httpd.x86_64 0:2.4.10-2.fc20 will be installed --> Processing Dependency: httpd-tools = 2.4.10-2.fc20 for package: httpd-2.4.10-2.fc20.x86_64 --> Processing Dependency: system-logos-httpd for package: httpd-2.4.10-2.fc20.x86_64 --> Running transaction check ---> Package fedora-logos-httpd.noarch 0:21.0.1-1.fc20 will be installed ---> Package httpd-tools.x86_64 0:2.4.10-2.fc20 will be installed --> Finished Dependency Resolution Dependencies Resolved ================================================================================ Package Arch Version Repository Size ================================================================================ Installing: httpd x86_64 2.4.10-2.fc20 updates 1.2 M Installing for dependencies: fedora-logos-httpd noarch 21.0.1-1.fc20 fedora 28 k httpd-tools x86_64 2.4.10-2.fc20 updates 79 k Transaction Summary ================================================================================ Install 1 Package (+2 Dependent packages) Total download size: 1.3 M Installed size: 4.0 M Is this ok [y/d/N]: y Downloading packages: (1/3): fedora-logos-httpd-21.0.1-1.fc20.noarch.rpm | 28 kB 00:00 (2/3): httpd-2.4.10-2.fc20.x86_64.rpm | 1.2 MB 00:01 (3/3): httpd-tools-2.4.10-2.fc20.x86_64.rpm | 79 kB 00:00 -------------------------------------------------------------------------------- Total 815 kB/s | 1.3 MB 00:01 Running transaction check Running transaction test Transaction test succeeded Running transaction (shutdown inhibited) Installing : httpd-tools-2.4.10-2.fc20.x86_64 1/3 Installing : fedora-logos-httpd-21.0.1-1.fc20.noarch 2/3 Installing : httpd-2.4.10-2.fc20.x86_64 3/3 Verifying : httpd-2.4.10-2.fc20.x86_64 1/3 Verifying : fedora-logos-httpd-21.0.1-1.fc20.noarch 2/3 Verifying : httpd-tools-2.4.10-2.fc20.x86_64 3/3 Installed: httpd.x86_64 0:2.4.10-2.fc20 Dependency Installed: fedora-logos-httpd.noarch 0:21.0.1-1.fc20 httpd-tools.x86_64 0:2.4.10-2.fc20 Complete! |
Next, you install php as the root user with the following command:
yum install php |
The following displays when you install php, and you need to reply with a y to complete the installation:
Loaded plugins: langpacks, refresh-packagekit Resolving Dependencies --> Running transaction check ---> Package php.x86_64 0:5.5.22-1.fc20 will be installed --> Processing Dependency: php-common(x86-64) = 5.5.22-1.fc20 for package: php-5.5.22-1.fc20.x86_64 --> Processing Dependency: php-cli(x86-64) = 5.5.22-1.fc20 for package: php-5.5.22-1.fc20.x86_64 --> Running transaction check ---> Package php-cli.x86_64 0:5.5.22-1.fc20 will be installed ---> Package php-common.x86_64 0:5.5.22-1.fc20 will be installed --> Processing Dependency: php-pecl-jsonc(x86-64) for package: php-common-5.5.22-1.fc20.x86_64 --> Running transaction check ---> Package php-pecl-jsonc.x86_64 0:1.3.6-1.fc20 will be installed --> Processing Dependency: /usr/bin/pecl for package: php-pecl-jsonc-1.3.6-1.fc20.x86_64 --> Processing Dependency: /usr/bin/pecl for package: php-pecl-jsonc-1.3.6-1.fc20.x86_64 --> Running transaction check ---> Package php-pear.noarch 1:1.9.5-6.fc20 will be installed --> Processing Dependency: php-xml for package: 1:php-pear-1.9.5-6.fc20.noarch --> Processing Dependency: php-posix for package: 1:php-pear-1.9.5-6.fc20.noarch --> Running transaction check ---> Package php-process.x86_64 0:5.5.22-1.fc20 will be installed ---> Package php-xml.x86_64 0:5.5.22-1.fc20 will be installed --> Finished Dependency Resolution Dependencies Resolved ================================================================================ Package Arch Version Repository Size ================================================================================ Installing: php x86_64 5.5.22-1.fc20 updates 2.6 M Installing for dependencies: php-cli x86_64 5.5.22-1.fc20 updates 3.9 M php-common x86_64 5.5.22-1.fc20 updates 1.0 M php-pear noarch 1:1.9.5-6.fc20 updates 343 k php-pecl-jsonc x86_64 1.3.6-1.fc20 updates 34 k php-process x86_64 5.5.22-1.fc20 updates 77 k php-xml x86_64 5.5.22-1.fc20 updates 247 k Transaction Summary ================================================================================ Install 1 Package (+6 Dependent packages) Total download size: 8.2 M Installed size: 32 M Is this ok [y/d/N]: y Downloading packages: (1/7): php-5.5.22-1.fc20.x86_64.rpm | 2.6 MB 00:03 (2/7): php-cli-5.5.22-1.fc20.x86_64.rpm | 3.9 MB 00:03 (3/7): php-common-5.5.22-1.fc20.x86_64.rpm | 1.0 MB 00:00 (4/7): php-pear-1.9.5-6.fc20.noarch.rpm | 343 kB 00:00 (5/7): php-pecl-jsonc-1.3.6-1.fc20.x86_64.rpm | 34 kB 00:00 (6/7): php-process-5.5.22-1.fc20.x86_64.rpm | 77 kB 00:00 (7/7): php-xml-5.5.22-1.fc20.x86_64.rpm | 247 kB 00:00 -------------------------------------------------------------------------------- Total 1.1 MB/s | 8.2 MB 00:07 Running transaction check Running transaction test Transaction test succeeded Running transaction (shutdown inhibited) Installing : php-cli-5.5.22-1.fc20.x86_64 1/7 Installing : php-process-5.5.22-1.fc20.x86_64 2/7 Installing : php-xml-5.5.22-1.fc20.x86_64 3/7 Installing : 1:php-pear-1.9.5-6.fc20.noarch 4/7 Installing : php-common-5.5.22-1.fc20.x86_64 5/7 Installing : php-pecl-jsonc-1.3.6-1.fc20.x86_64 6/7 Installing : php-5.5.22-1.fc20.x86_64 7/7 Verifying : php-5.5.22-1.fc20.x86_64 1/7 Verifying : php-common-5.5.22-1.fc20.x86_64 2/7 Verifying : php-cli-5.5.22-1.fc20.x86_64 3/7 Verifying : 1:php-pear-1.9.5-6.fc20.noarch 4/7 Verifying : php-process-5.5.22-1.fc20.x86_64 5/7 Verifying : php-xml-5.5.22-1.fc20.x86_64 6/7 Verifying : php-pecl-jsonc-1.3.6-1.fc20.x86_64 7/7 Installed: php.x86_64 0:5.5.22-1.fc20 Dependency Installed: php-cli.x86_64 0:5.5.22-1.fc20 php-common.x86_64 0:5.5.22-1.fc20 php-pear.noarch 1:1.9.5-6.fc20 php-pecl-jsonc.x86_64 0:1.3.6-1.fc20 php-process.x86_64 0:5.5.22-1.fc20 php-xml.x86_64 0:5.5.22-1.fc20 Complete! |
After installing the software, you can set the Apache server to start automatically with the following command:
chkconfig httpd on |
However, that command only starts the Apache server the next time you boot the server. You use the following command as the root user to start the Apache server:
apachectl start |
You can verify the installation with the following command as the root user:
ps -ef | grep httpd | grep -v grep |
It should return:
root 5433 1 0 17:03 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 5434 5433 0 17:03 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 5435 5433 0 17:03 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 5436 5433 0 17:03 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 5437 5433 0 17:03 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 5438 5433 0 17:03 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 5442 5433 0 17:03 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND |
and, then verify the listening port with the following command as the root user:
netstat -tulpn | grep :80 |
It should return the following when both the Apache server is listening on port 80 and the Oracle multi-protocol server is listening on port 8080:
tcp6 0 0 :::80 :::* LISTEN 5433/httpd tcp6 0 0 :::8080 :::* LISTEN 1505/tnslsnr |
After verifying the connection, you can test it by creating the traditional info.php program file in the /var/www/http directory. The file should contain the following:
1 2 3 | <?php phpinfo(); ?> |
You can test it by opening the Firefox browser and entering the following URL from the Fedora Linux image:
http://localhost/info.php |
It should display the typical diagnostic page. This verifies the configuration of the Apache and PHP servers. The next step verifies whether you have the mysqli library to connect to the MySQL database.
You create a mysqli_check.php script, 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 | <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
if (!function_exists('mysqli_init') && !extension_loaded('mysqli')) {
print 'mysqli not installed.'; }
else {
print 'mysqli installed.'; }
?>
</script>
</body>
</html> |
You can test it with the following URL from the local browser:
http://localhost/mysqli_check.php |
If it’s installed you can skip the next step, but if not you need to run yum in expert mode as follows (the check for php-mysql isn’t really necessary because it’s too old a version but good practice):
[root@localhost etc]# yum shell Loaded plugins: langpacks, refresh-packagekit > remove php-mysql No Match for argument: php-mysql > install php-mysqlnd > run --> Running transaction check ---> Package php-mysqlnd.x86_64 0:5.5.22-1.fc20 will be installed --> Processing Dependency: php-pdo(x86-64) = 5.5.22-1.fc20 for package: php-mysqlnd-5.5.22-1.fc20.x86_64 --> Running transaction check ---> Package php-pdo.x86_64 0:5.5.22-1.fc20 will be installed --> Finished Dependency Resolution ================================================================================ Package Arch Version Repository Size ================================================================================ Installing: php-mysqlnd x86_64 5.5.22-1.fc20 updates 293 k Installing for dependencies: php-pdo x86_64 5.5.22-1.fc20 updates 141 k Transaction Summary ================================================================================ Install 1 Package (+1 Dependent package) Total download size: 433 k Installed size: 1.4 M Is this ok [y/d/N]: y Downloading packages: (1/2): php-mysqlnd-5.5.22-1.fc20.x86_64.rpm | 293 kB 00:00 (2/2): php-pdo-5.5.22-1.fc20.x86_64.rpm | 141 kB 00:00 -------------------------------------------------------------------------------- Total 427 kB/s | 433 kB 00:01 Running transaction check Running transaction test Transaction test succeeded Running transaction (shutdown inhibited) Installing : php-pdo-5.5.22-1.fc20.x86_64 1/2 Installing : php-mysqlnd-5.5.22-1.fc20.x86_64 2/2 Verifying : php-pdo-5.5.22-1.fc20.x86_64 1/2 Verifying : php-mysqlnd-5.5.22-1.fc20.x86_64 2/2 Installed: php-mysqlnd.x86_64 0:5.5.22-1.fc20 Dependency Installed: php-pdo.x86_64 0:5.5.22-1.fc20 Finished Transaction > quit |
You should note that this also installed PDO. One caveat, before you rerun the mysqli_check.php script from a browser, you need to restart the Apache server. You can do that as the root user with the following syntax:
apachectl restart |
You can retest it with the following URL from the local browser:
http://localhost/mysqli_check.php |
At this point you should have everything installed to test your connection the MySQL database. As mentioned, this example extends my instructions for installing MySQL on the Fedora instance.
The following query.php file tests your ability to connect to the MySQL database with the mysqli driver, and it uses the studentdb and video store example from my Oracle Database 11g and MySQL 5.6 Developer Handbook:
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 | <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> |
This should display the following in the browser:
You can see how to open port 80 for the Apache server in this blog post. If you want to work with blob data types, you’ll also need to use yum to install the php-gd library. You can read my LAMP php-gd library blog post to learn how to install the libraries. As always, I hope a step-by-step approach without assumptions helps those learning MySQL.
Lowercase Table Names
A student posed the question about why table names are case sensitive. That’s because case sensitive table names are the default installation, as qualified in the MySQL documentation. You can verify that with the following query:
SELECT CASE WHEN @@lower_case_table_names = 1 THEN 'Case insensitive tables' ELSE 'Case sensitive tables.' END AS "Table Name Status"; |
The default value returned on Linux is:
+------------------------+ | Table Name Status | +------------------------+ | Case sensitive tables. | +------------------------+ 1 row in set (0.00 sec) |
The default value for the lower_case_table_names value on the Windows OS is 1 not 0 because you can inadvertently create a lowercase and case sensitive table when you write an INSERT statement and use a lowercase table name. I’ve provided that detail in a reply comment to this blog post.
You can change the default by adding the following parameter in the my.cnf file on Linux or the my.ini file on Windows:
# Make all tables case insensitive. lower_case_table_names=1 |
This lets you enter tables in upper or mixed case, and stores them in the data catalog as lowercase table names.
PostgreSQL Composites
PostgreSQL like Oracle supports record data types but unlike Oracle, PostgreSQL doesn’t support collections of record data types. Here’s an example of how to define a PostgreSQL composite data type, and how to use it as a column’s data type.
CREATE TYPE address_type AS ( street_address VARCHAR , city VARCHAR , state VARCHAR , zip_code VARCHAR ); |
Then, you define an ADDRESS table, like:
CREATE TABLE address ( address_id SERIAL , address_struct ADDRESS_TYPE ); |
You can now insert rows like:
-- Insert the first row. INSERT INTO address ( address_struct ) VALUES (('52 Hubble Street','Lexington','KY','40511-1225')); -- Insert the second row. INSERT INTO address ( address_struct ) VALUES (('54 Hubble Street','Lexington','KY','40511-1225')); |
Then, you can query them like this:
SELECT * FROM address; |
It returns:
address_id | address_struct
------------+----------------------------------------------
1 | ("52 Hubble Street",Lexington,KY,40511-1225)
2 | ("54 Hubble Street",Lexington,KY,40511-1225)
(2 rows) |
You must use parentheses around the ADDRESS_STRUCT column to query individual items, like:
SELECT address_id , (address_struct).street_address , (address_struct).city , (address_struct).state , (address_struct).zip_code FROM address; |
It returns output like a table:
address_id | street_address | city | state | zip_code
------------+------------------+-----------+-------+------------
1 | 52 Hubble Street | Lexington | KY | 40511-1225
2 | 54 Hubble Street | Lexington | KY | 40511-1225
(2 rows) |
While you can define a table that holds an array of a composite type, there’s no syntax that appears to work with an array of a composite type. I hope this helps those interested in implementing record structures in PostgreSQL.
PostgreSQL Auto IDs
PostgreSQL’s approach to automatic numbering is as simple as Oracle but different than MySQL, and Microsoft SQL Server. For example, you have a two-step process with Oracle, PostgreSQL, MySQL, and Microsoft SQL Server. First, you create an Oracle table with the GENERATED AS IDENTITY clause, a PostgreSQL table with the SERIAL data type, a MySQL table with the AUTO_INCREMENT clause, and a Microsoft SQL Server table with the IDENTITY(1,1) clause. Then, you need to write an INSERT statement for Oracle, MySQL, or Microsoft SQL Server like:
- Oracle’s
INSERTstatement excludes the auto-incrementing column from the list of columns or provides aNULLvalue in theVALUES-list. You can then assign theRETURNING INTOresult from anINSERTstatement to a session-level (bind) variable. - MySQL’s
INSERTstatement excludes the auto-incrementing column from the list of columns or provides aNULLvalue in theVALUES-list. You can then assign theLAST_INSERT_ID()function value to a session-level variable, and populate a foreign key column. - Microsoft SQL Server’s
INSERTstatement excludes the auto-incrementing column from the list of columns or provides aNULLvalue in theVALUES-list. You can then assign theSCOPE_IDENTITY()function’s value to a session-level variable, and populate a foreign key column.
PostgreSQL differs because it works differently between the SQL and PL/pgSQL contexts. Let’s look at how you link the insert of data into two tables in both contexts.
The following PostgreSQL syntax creates an ADDRESS table with an auto incrementing ADDRESS_ID column that uses a SERIAL data type, which acts like an auto numbering column:
/* Create a customer table. */ CREATE TABLE customer ( customer_id SERIAL CONSTRAINT customer_pk PRIMARY KEY , first_name VARCHAR(20) , last_name VARCHAR(20)); /* Create an address table. */ CREATE TABLE address ( address_id SERIAL CONSTRAINT address_pk PRIMARY KEY , customer_id INTEGER , street_address VARCHAR(40) , city VARCHAR(30) , state VARCHAR(8) , zip_code VARCHAR(10)); |
If you want to insert one row into the CUSTOMER table and a related row in the ADDRESS table. You have two possible approaches. One works in both the SQL and PL/pgSQL contexts. That mechanism requires you to use a scalar subquery to capture the foreign key value of the CUSTOMER_ID column in the ADDRESS table, like this:
/* Insert into customer table. */ INSERT INTO customer ( first_name, last_name ) VALUES ('F. Scott','Fitzgerald'); /* Insert into address table. */ INSERT INTO address ( customer_id , street_address , city , state , zip_code ) VALUES ((SELECT customer_id FROM customer WHERE first_name = 'F. Scott' AND last_name = 'Fitzgerald') ,'599 Summit Avenue' ,'St. Paul' ,'Minnesota' ,'55102'); |
The RETURNING INTO clause of PostgreSQL only works in a PL/pgSQL context, like this:
DO $$ DECLARE lv_customer_id INTEGER; BEGIN /* Insert into customer table. */ INSERT INTO customer ( first_name, last_name ) VALUES ('Madeleine','Smith') RETURNING customer_id INTO lv_customer_id; /* Insert into address table. */ INSERT INTO address ( customer_id , street_address , city , state , zip_code ) VALUES ( lv_customer_id ,'7 Blythswood Square' ,'Glasgow' ,'Scotland' ,'G2 4BG'); /* Manage any exceptions. */ EXCEPTION WHEN OTHERS THEN RAISE NOTICE '% %', SQLERRM, SQLSTATE; END$$; |
You query the auto generated values and data from the INSERT statement to the CUSTOMER table with a scalar subquery against the natural key (the FIRST_NAME and LAST_NAME columns) from the ADDRESS table. The following is an example of such a query:
SELECT * FROM customer c INNER JOIN address a ON c.customer_id = a.customer_id; |
It returns:
customer_id | first_name | last_name | address_id | customer_id | street_address | city | state | zip_code
-------------+------------+------------+------------+-------------+---------------------+----------+-----------+----------
1 | F. Scott | Fitzgerald | 1 | 1 | 599 Summit Avenue | St. Paul | Minnesota | 55102
2 | Madeleine | Smith | 2 | 2 | 7 Blythswood Square | Glasgow | Scotland | G2 4BG
(2 rows) |
My take is that the RETURNING column_value INTO local_value clause is a better approach than using Oracle’s .NEXTVAL and .CURRVAL values. I also think the RETURNING INTO clause is a better approach than using MySQL’s LAST_INSERT_ID() or Microsoft SQL Server’s SCOPE_IDENTITY().
Initially, I felt it was odd that the PostgreSQL disallows the RETURNING INTO clause in a SQL context, because it allows the syntax in a PL/pgSQL context. After some reflection the choice makes more sense because most developers work within a procedural context when they use transactions across two or more tables. PL/pgSQL is PostgreSQL’s procedural context from managing transactions across two or more tables.
As always, I hope this helps.
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