Archive for the ‘MySQL’ Category
The LinkedIn MySQL DB Development group posed a questions on how to handle images. Naturally, the argument always goes: Should images be deployed in the database or the file system? I believe they should be stored in the database because the cost and time associated is too high with regard to managing files, a file naming schema, and backing up the file system discretely from the database.
Since there’s a significant difference between the backup of transactional data and image data, they should be placed in different databases. The
imagedb database is where you would place the images and large text descriptions, as shown in the MySQL Workbench ERD:
The imagedb ERD splits the foreign key references back to the
system_user table, which contains the individual user credentials. The
system_user table serves as the Access Control List (ACL) for the application.
Until I get a chance to write the code for this model, you can refer to the generic PHP/MySQL solution from several years back (its code source was last tested with PHP 5.3). As always, I hope this helps.
As I review with my students, a stored function works like a standalone program, while a stored procedure runs in the scope of another program unit. For example, you can compare the result of a function as an expression in an
IF statement, like:
IF add_numbers(1,3) > 3 THEN ... ELSE ... END IF;
You can’t call procedures inside an
IF statement, but you can call the procedure and use a single
OUT-mode (pass-by-reference) parameter from the procedure in a subsequent
IF statement. You can implement a a wait procedure like that with the following example.
The example first creates two tables, the
-- Drop road_runner table if exists. DROP TABLE IF EXISTS road_runner; -- Create roadrunner table. CREATE TABLE road_runner ( road_runner_id int unsigned auto_increment primary key , road_runner_text varchar(20) , CONSTRAINT road_runner_nk UNIQUE (road_runner_text)); -- Drop coyote table if exists. DROP TABLE IF EXISTS coyote; -- Create coyote table. CREATE TABLE coyote ( coyote_id int unsigned auto_increment primary key , coyote_text varchar(20) , road_runner_id int unsigned , CONSTRAINT coyote_nk UNIQUE (coyote_text));
The following creates a procedure that:
- Writes data to two tables when the values are unique, returning a value of zero when it works.
- Writes data to neither table when the values to either table are non-unique, returning a value of one when it fails.
The procedure uses a
0 as a false value and a
1 as a true value. The use of a 0 and 1 for truth is a consistent approach for languages where they don’t support a Boolean data type.
-- Change the delimiter to a "$$" DELIMITER $$ -- Drop the paired procedure. DROP PROCEDURE IF EXISTS two_table$$ -- Create the paired procedure. CREATE PROCEDURE two_table (IN pv_road_runner_text varchar(20) ,IN pv_coyote_text varchar(20) , OUT pv_confirm_it int) BEGIN /* Declare a variable to hold a sequence value for an auto incrementing value. */ DECLARE lv_road_runner_id int unsigned; /* Declare a condition variable for attempting to write a non-unique record to a table. */ DECLARE duplicate CONDITION FOR 1062; /* Declare an event handler for a duplicate condition variable, rollback transaction, and set 1 as a false condition. */ DECLARE EXIT HANDLER FOR duplicate BEGIN ROLLBACK to all_or_none; SET pv_confirm_it = 1; END; /* Start the transaction. */ START TRANSACTION; /* Set the save point for a multiple table transaction. */ SAVEPOINT all_or_none; /* Insert into road runner table. */ INSERT INTO road_runner (road_runner_text) VALUES (pv_road_runner_text); /* Capture the auto incrementing sequence value as a local variable. */ SET lv_road_runner_id := last_insert_id(); /* Insert into the coyote table. */ INSERT INTO coyote (coyote_text ,road_runner_id) VALUES (pv_coyote_text ,lv_road_runner_id); /* Commit the record. */ COMMIT; /* Set the control variable to a true value. */ SET pv_confirm_it := 0; END; $$ DELIMITER ;
You can test the pass-by-reference procedure with the following code:
-- Set a control variable with a null value. SET @sv_control := null; -- Query the results from a join between the road_runner and coyote tables. SELECT * FROM road_runner r INNER JOIN coyote c ON r.road_runner_id = c.road_runner_id; -- Call the two_table procedure with unique results. CALL two_table('Road Runner 1','Coyote 1',@sv_control); -- Query the control variable result from the second call to the -- two_table procedure. SELECT @sv_control AS "1st Insert"; -- Reset the value for a second test. SET @sv_control := 0; -- Call teh two_table procedure with unique results. CALL two_table('Road Runner 2','Coyote 1',@sv_control); -- Query the results from a join between the road_runner and coyote tables. SELECT * FROM road_runner r INNER JOIN coyote c ON r.road_runner_id = c.road_runner_id; -- Query the control variable result from the second call to the -- two_table procedure. SELECT @sv_control AS "2nd Insert";
I hope this helps anybody trying to implement a pass-by-reference procedure with a control variable. You can find other examples in Chapter 14 of Oracle Database 11g and MySQL 5.6 Developer Handbook (pp. 446-449 and 450-451).
My students required way to remove all their tables, views, and constraints from a MySQL
database (or the alias
schema). Since they’re using referential or foreign key constraints, I also wrote one procedure to drop all foreign key constraints from a database. There’s also another to drop views. The final stored procedure calls the procedure that drops foreign keys, then calls the procedure to drop views before dropping all the tables.
dropForeignKeys stored procedure, but if you want to capture
ALTER statements that add these back later please check my follow-up Capture MySQL Foreign Keys post.
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-- Provide a log file debugging statement. SELECT 'DROP PROCEDURE IF EXISTS dropForeignKeys'; -- Conditionally drop the procedure. DROP PROCEDURE IF EXISTS dropForeignKeys; -- Provide a log file debugging statement. SELECT 'CREATE PROCEDURE dropForeignKeys'; -- Change delimiter to create procedure. DELIMITER $$ -- Create procedure. CREATE PROCEDURE dropForeignKeys ( pv_database VARCHAR(64) , pv_referenced_table VARCHAR(64)) BEGIN /* Declare local statement variables. */ DECLARE lv_stmt VARCHAR(1024); /* Declare local cursor variables. */ DECLARE lv_table_name VARCHAR(64); DECLARE lv_constraint_name VARCHAR(64); /* Declare control variable for handler. */ DECLARE fetched INT DEFAULT 0; /* Declare local cursor. */ DECLARE foreign_key_cursor CURSOR FOR SELECT rc.table_name , rc.constraint_name FROM information_schema.referential_constraints rc WHERE constraint_schema = IFNULL(pv_database,database()) AND referenced_table_name = pv_referenced_table ORDER BY rc.table_name , rc.constraint_name; /* Declare a not found record handler to close a cursor loop. */ DECLARE CONTINUE HANDLER FOR NOT FOUND SET fetched = 1; /* Open a local cursor. */ OPEN foreign_key_cursor; cursor_foreign_key: LOOP FETCH foreign_key_cursor INTO lv_table_name , lv_constraint_name; /* Place the catch handler for no more rows found immediately after the fetch operation. */ IF fetched = 1 THEN LEAVE cursor_foreign_key; END IF; /* Set a SQL statement by using concatenation. */ SET @SQL := CONCAT('ALTER TABLE',' ',lv_table_name,' ','DROP FOREIGN KEY',' ',lv_constraint_name); /* Prepare, run, and deallocate statement. */ PREPARE lv_stmt FROM @SQL; EXECUTE lv_stmt; DEALLOCATE PREPARE lv_stmt; END LOOP cursor_foreign_key; CLOSE foreign_key_cursor; END; $$ -- Reset delimiter to run SQL statements. DELIMITER ;
dropViews stored procedure:
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-- Provide a log file debugging statement. SELECT 'DROP PROCEDURE IF EXISTS dropViews'; -- Conditionally drop the procedure. DROP PROCEDURE IF EXISTS dropViews; -- Provide a log file debugging statement. SELECT 'CREATE PROCEDURE dropViews'; -- Change delimiter to create procedure. DELIMITER $$ -- Create procedure. CREATE PROCEDURE dropViews ( pv_database VARCHAR(64)) BEGIN /* Declare local statement variables. */ DECLARE lv_stmt VARCHAR(1024); /* Declare local cursor variables. */ DECLARE lv_view_name VARCHAR(64); /* Declare control variable for handler. */ DECLARE fetched INT DEFAULT 0; /* Declare local cursor. */ DECLARE view_cursor CURSOR FOR SELECT v.table_name FROM information_schema.views v WHERE table_schema = IFNULL(pv_database, database()) ORDER BY v.table_name; /* Declare a not found record handler to close a cursor loop. */ DECLARE CONTINUE HANDLER FOR NOT FOUND SET fetched = 1; /* Open a local cursor. */ OPEN view_cursor; cursor_view: LOOP FETCH view_cursor INTO lv_view_name; /* Place the catch handler for no more rows found immediately after the fetch operation. */ IF fetched = 1 THEN LEAVE cursor_view; END IF; /* Set a SQL statement by using concatenation. */ SET @SQL := CONCAT('DROP VIEW',' ',lv_view_name); /* Prepare, run, and deallocate statement. */ PREPARE lv_stmt FROM @SQL; EXECUTE lv_stmt; DEALLOCATE PREPARE lv_stmt; END LOOP cursor_view; CLOSE view_cursor; END; $$ -- Reset delimiter to run SQL statements. DELIMITER ;
dropTables stored procedure:
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CREATE PROCEDURE dropTables ( pv_database VARCHAR(64)) BEGIN /* Declare local statement variables. */ DECLARE lv_stmt VARCHAR(1024); /* Declare local cursor variables. */ DECLARE lv_table_name VARCHAR(64); /* Declare control variable for handler. */ DECLARE fetched INT DEFAULT 0; /* Declare local cursor. */ DECLARE table_cursor CURSOR FOR SELECT t.table_name FROM information_schema.tables t WHERE table_schema = IFNULL(pv_database, database()) ORDER BY t.table_name; /* Declare a not found record handler to close a cursor loop. */ DECLARE CONTINUE HANDLER FOR NOT FOUND SET fetched = 1; /* Drop the views. */ CALL dropViews(null); /* Open a local cursor. */ OPEN table_cursor; cursor_table: LOOP FETCH table_cursor INTO lv_table_name; /* Place the catch handler for no more rows found immediately after the fetch operation. */ IF fetched = 1 THEN LEAVE cursor_table; END IF; /* Drop the tables. */ CALL dropForeignKeys(null,lv_table_name); /* Set a SQL statement by using concatenation. */ SET @SQL := CONCAT('DROP TABLE',' ',lv_table_name); /* Prepare, run, and deallocate statement. */ PREPARE lv_stmt FROM @SQL; EXECUTE lv_stmt; DEALLOCATE PREPARE lv_stmt; END LOOP cursor_table; CLOSE table_cursor; END; $$ -- Reset delimiter to run SQL statements. DELIMITER ;
You put these in a rerunnable script, run it, and then call the
dropTables stored procedure. You can pass a database (or schema) name or a
null value. When you pass a
null value, it uses the current database, like:
As always, I hope this helps others.
In teaching, I had a problem because my students have different base operating systems, like Windows 7, Windows 8, Linux, and Mac OS X. I needed a teaching and lecture platform that would let me teach it all (not to mention support their environments). That meant it had to virtualize any of the following with a portable device:
- Windows 7 or 8 hosting natively an Oracle Database 11g XE, 11g, or 12c and MySQL Database 5.6
- Windows 7 or 8 hosting a Fedora or Oracle Unbreakable Linux VM (3 or 4 GB) with Oracle Database 11g XE, 11g, or 12c and MySQL Database 5.6
- Mac OS X hosting a Fedora or Oracle Unbreakable Linux VM (3 or 4 GB) with Oracle Database 11g XE, 11g, or 12c and MySQL Database 5.6
- Ubuntu hosting a Fedora or Oracle Unbreakable Linux VM (3 or 4 GB) with Oracle Database 11g XE, 11g, or 12c and MySQL Database 5.6
I never considered a manufacturer other than Apple for a laptop since they adopted the Intel chip. Too many of the others sell non-hyperthreaded laptop machines that they market as i5 or i7 64-bit OS machines when they’re not. Some of those vendors disable the hyperthreading facility while others provide motherboards that can’t support hyperthreading. The ones I dislike the most provide a BIOS setting that gives the impression you can enable hyperthreading when you can’t. All Apple devices, MacBook, MacBook Pro, Mac Mini, and Mac Pro do fully support a 64-bit OS and their virtualization.
A MacBook Pro came to mind but the disk space requirements were 1 TB, and that’s too pricey. I went with the Mac Mini because with 16 GB of memory and a 1 TB drive it was only $1,200. Add a wireless keyboard and mighty mouse, and an HDMI and mini-DVI connections, and I had my solution. Naturally, my desktop is a one generation old Mac Pro with 64 GB of memory and 12 TB of disk space, which supports all the virtual machines used for testing. Note to Apple marketing staff: The prior version of the Mac Pro let you pay reasonable (3rd party) prices for the additional memory and disk drives.
The Mac Mini means I can travel anywhere and plug into the console and demo tools and techniques from a myriad set of platforms without the hassle of moving on and off to frequently VM images. It’s a great solution with only one downside, HDMI to DVI sometimes creates purple toned screens. It’s unfortunate because some venues have monitors that don’t support HDMI).
Since MySQL Workbench 6.0 isn’t available for Fedora, Version 20, I’m having my students install it on their local Windows and Mac OS X operating systems. You can configure the
/etc/sysconfig/iptables file to enable port 3306 after installing MySQL on Fedora.
You can open a port by using the
firewall-config utility (easy way) or by adding the following line to the
/etc/sysconfig/iptables file (Fedora’s instructions on editing
iptables [hard way]). The file won’t exist initially, but you can create it by running the following command as the
root superuser or sudoer:
shell> service iptables save
You you can run the following commands as the
root superuser, which saves the line in the
shell> iptables -A INPUT -m conntrack --ctstate NEW -m tcp -p tcp --dport 3306 -j ACCEPT shell> iptables-save
After making the change to the
/etc/iptables file you can change the firewall by running the following command as the
shell> service iptables restart
Just make sure you don’t inadvertently start both iptables and ip6tables as services. You can check that only one is running by using the following commands:
shell> service iptables status shell> service ip6tables status
MySQL Workbench Configuration
- The first thing you need to do is click on the
+symbol in the circle to the right of the MySQL Connections text label. It launches the Setup New Connection dialog.
- The second thing you need to do is enter a Connection Name, Hostname, Port, and Username. Then, click the Test Connection button.
- The Test Connection button launches the Connect to MySQL Server dialog. Enter the password for the
studentuser (or whatever user you’re interested in), and then click the OK button.
- When the credentials in the Connect to MySQL Server dialog work, you see the following confirmation dialog message. Click the OK button to continue and you’ll see a new VMWare Fedora Instance connection icon.
- Click the VMWare Fedora Instance connection to start a new connection.
- The VMWare Fedora Instance button launches the Connect to MySQL Server dialog. Like you did when configuring the connection, enter the password for the
studentuser (or whatever user you’re interested in), and then click the OK button. It launches an interactive panel that lets you run, edit, or save the SQL script file.
- Type the following two lines in the Query1 panel (at least if you have a
USE studentdb; SELECT DATABASE();
I built a new image on VMWare Fusion for my class, which required installing MySQL 5.6 on Fedora, Version 20. If you don’t know how to add your user to the
sudoers list, you should check this older and recently updated blog post.
- Download the MySQL Yum Repository and launch the downloaded RPM.
- Install MySQL on Fedora, Version 20, which you can find with the following command:
shell> rpm -qa | grep mysql mysql-community-release-fc20-5.noarch
fc20-5 changes with point releases, but assuming that you’re installing the
shell> sudo yum localinstall mysql-community-release-fc20-5.noarch.rpm
- Install MySQL on Fedora with the following command:
shell> sudo yum install mysql-server
- Start the MySQL service on Fedora with the following command:
shell> sudo service mysqld start
- Secure the MySQL installation with the following command:
- Set the MySQL Service to start with the Fedora operating system with the following command (not
shell> sudo systemctl enable mysqld.service
It sets the following two links:
ln -s '/usr/lib/systemd/system/mysqld.service' '/etc/systemd/system/mysql.service' ln -s '/usr/lib/systemd/system/mysqld.service' '/etc/systemd/system/multi-user.target.wants/mysqld.service'
Restart the Fedora operating system to effect the changes.
- Reset the MySQL configuration file to enable external connections through Port 3306 with the following changes to the my:
Remark out the
socket line, like this:
port lines below after you know the actual IP address of the server to the
my.cnf file in the
You substitute the actual IP address for the
nnn.nnn.nnn.nnn on the
bind_address line with the actual IP address returned by the
ifconfig command, like this:
Then, add these two lines to the my.cnf file.
It’s actually easier to use localhost.localdomain than an IP address when you use DHCP, like:
If you plan to connect from a host system, like Windows or Mac OS X, to a virtual Linux environment using DHCP, change
- Restart the mysqld service with the following syntax:
shell> sudo service mysqld restart
You can check whether MySQL is listening on Port 3306 with this syntax:
shell> sudo netstat –anp | grep 3306
tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 1311/mysqld
Go to this page if you want to install MySQL Workbench.
I’ve worked with every release of Microsoft Excel, and I know it takes effort to keep up to date with certain releases. Clearly, the Data Analysis eXpression (DAX) Language introduced in Excel 2010 went unnoticed by many, which was sad. DAX is truly a powerful extension to the analytical and modeling approaches in Microsoft Excel.
I’d like to recommend Microsoft Excel 2013 Building Data Models with PowerPivot to those who haven’t learned how to use DAX in Excel 2010, 2011, or 2013. DAX works with tables but if you don’t use tables, I guess you can skip DAX because you must have infinite time to produce marginal analytical outcomes (tongue in cheek humor). However, if you’re like most folks, you want a book to get you up-to-speed quickly, and that’s what this book will do for you.
Just one caveat if you’re using an Oracle or MySQL database, use the prepackaged analytic functions before you download the data set. You should always pre-select data before applying analytics in Excel. Remember the more refined the data model you start with the easier it is to structure analytical tools to leverage the data model. While DAX is powerful, it doesn’t replace the speed and query optimized behaviors of effective Oracle or MySQL queries.
Somebody asked how to create a
SYNONYM in MySQL, which is interesting because MySQL doesn’t support synonyms. I thought the prior entry explained how to do it, but here’s a new post. However, you can create a view in one database that relies on a table in another database.
The following SQL statements create two databases and grant appropriate privileges to the
student as the
/* Create two databases. */ CREATE DATABASE seussdb; CREATE DATABASE appdb; /* Grant privileges to a student user. */ GRANT ALL ON seussdb.* TO student; GRANT ALL ON appdb.* TO student;
Log out from the
root superuser and reconnect as the
student user. Then, the following code connects to the
seuss database and create a
hat table; and inserts two rows into the
/* Use the appdb database. */ USE seussdb; /* Create a hat table. */ CREATE TABLE hat ( hat_id INT UNSIGNED PRIMARY KEY AUTO_INCREMENT , hat_text VARCHAR(20)); /* Insert two rows into the hat table. */ INSERT INTO hat (hat_text) VALUES ('Thing 1'); INSERT INTO hat (hat_text) VALUES ('Thing 2');
The following code connects to the
application database and creates a
hat view; and then the code inserts one additional row into the
/* Connect to the application database. */ USE appdb; /* Create a hat view. */ CREATE VIEW hat AS SELECT * FROM seussdb.hat; /* Query the contents of the view, or seuss.hat table. */ SELECT * FROM hat; /* Insert a new row into the hat table. */ INSERT INTO hat (hat_text) VALUES ('Thing 3'); /* Query the contents of the view, after insert to the view. */ SELECT * FROM hat;
The results will be the following:
+--------+----------+ | hat_id | hat_text | +--------+----------+ | 1 | Thing 1 | | 2 | Thing 2 | | 3 | Thing 3 | +--------+----------+
I hope this answers the question on how to mimic the Oracle database’s synonyms. The
appdb.hat view acts as a synonym to the
An acquaintance sent me this image from a cyber cafe or hotel in Russia. It says that my blog site is prohibited and violates Russian law, and that they’re blocking my site in accordance with the Russian Federal Law of 27.07.2006 No. 149-FZ.
All I can say is, “Wow!” I didn’t know that stuff about writing programs, web pages, and solving generic database and operating system problems was so sensitive. For that matter, I didn’t know what I post would interest any government. I half wonder whether my friend’s pulling my leg.
As I reflect on it, could it be that Oracle post on how to write an encrypted object type? or, how with proper OS credentials how you reset MySQL’s root password? or, how to verify a socket in Perl? Nah, it’s probably the one on how to set a static IP in Windows – that’s truly sensitive stuff. 😉
Does anybody who reads the blog have any clue about what would drive the Russian government to block a technology blog site like mine? My serious guess is that there is somebody who hosts with the same provider who’s done something tacky.
SQL tidbits are always valuable and highly searched for by newbies (as opposed to reading the SQL documentation). Sometimes we seasoned SQL developers take for granted little things like when a single- or multiple-character wildcard comparison works. It seems we know what newbies don’t. That you need a wildcard comparison operator not simply and equality comparison operator.
The question posed to me was, “Why doesn’t my wildcard comparison work?” Here’s a simplified example of their question.
SELECT 'Valid' AS "Test" FROM dual WHERE 'Treat' = 'Tre_t' OR 'Treet' = 'Tre_t';
Naturally, the answer is that the equality operator compares the strings based on their exact match (character sensitively in Oracle and character insensitively in MySQL). It needs to be rewritten by replacing the equals (
=) comparison operator with the
LIKE comparison operator. The following query does that:
SELECT 'Valid' AS "Test" FROM dual WHERE 'Treat' LIKE 'Tre_t' OR 'Treet' LIKE 'Tre_t'
The same behavior exists for the multiple-character wildcard (
%). I hope this helps those looking for this answer.