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2010-05-26T13:44:56Z

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2010-05-26T09:50:51Z

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== IS NOT NULL==



<source lang="sql">
mysql>
mysql> CREATE TABLE Topic(
-> TopicID SMALLINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> Name VARCHAR(50) NOT NULL,
-> InStock SMALLINT UNSIGNED NOT NULL,
-> OnOrder SMALLINT UNSIGNED NOT NULL,
-> Reserved SMALLINT UNSIGNED NOT NULL,
-> Department ENUM("Classical", "Popular") NOT NULL,
-> Category VARCHAR(20) NOT NULL,
-> RowUpdate TIMESTAMP NOT NULL
-> );
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql>
mysql> INSERT INTO Topic (Name, InStock, OnOrder, Reserved, Department, Category) VALUES
-> ("Java", 10, 5, 3, "Popular", "Rock"),
-> ("JavaScript", 10, 5, 3, "Classical", "Opera"),
-> ("C Sharp", 17, 4, 1, "Popular", "Jazz"),
-> ("C", 9, 4, 2, "Classical", "Dance"),
-> ("C++", 24, 2, 5, "Classical", "General"),
-> ("Perl", 16, 6, 8, "Classical", "Vocal"),
-> ("Python", 2, 25, 6, "Popular", "Blues"),
-> ("Php", 32, 3, 10, "Popular", "Jazz"),
-> ("ASP.net", 12, 15, 13, "Popular", "Country"),
-> ("VB.net", 5, 20, 10, "Popular", "New Age"),
-> ("VC.net", 24, 11, 14, "Popular", "New Age"),
-> ("UML", 42, 17, 17, "Classical", "General"),
-> ("www.sqle.ru",25, 44, 28, "Classical", "Dance"),
-> ("Oracle", 32, 15, 12, "Classical", "General"),
-> ("Pl/SQL", 20, 10, 5, "Classical", "Opera"),
-> ("Sql Server", 23, 12, 8, "Classical", "General");
Query OK, 16 rows affected (0.00 sec)
Records: 16 Duplicates: 0 Warnings: 0
mysql>
mysql> select * from Topic;
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| TopicID | Name | InStock | OnOrder | Reserved | Department | Category | RowUpdate |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| 1 | Java | 10 | 5 | 3 | Popular | Rock | 2007-07-23 19:09:46 |
| 2 | JavaScript | 10 | 5 | 3 | Classical | Opera | 2007-07-23 19:09:46 |
| 3 | C Sharp | 17 | 4 | 1 | Popular | Jazz | 2007-07-23 19:09:46 |
| 4 | C | 9 | 4 | 2 | Classical | Dance | 2007-07-23 19:09:46 |
| 5 | C++ | 24 | 2 | 5 | Classical | General | 2007-07-23 19:09:46 |
| 6 | Perl | 16 | 6 | 8 | Classical | Vocal | 2007-07-23 19:09:46 |
| 7 | Python | 2 | 25 | 6 | Popular | Blues | 2007-07-23 19:09:46 |
| 8 | Php | 32 | 3 | 10 | Popular | Jazz | 2007-07-23 19:09:46 |
| 9 | ASP.net | 12 | 15 | 13 | Popular | Country | 2007-07-23 19:09:46 |
| 10 | VB.net | 5 | 20 | 10 | Popular | New Age | 2007-07-23 19:09:46 |
| 11 | VC.net | 24 | 11 | 14 | Popular | New Age | 2007-07-23 19:09:46 |
| 12 | UML | 42 | 17 | 17 | Classical | General | 2007-07-23 19:09:46 |
| 13 | www.sqle.ru | 25 | 44 | 28 | Classical | Dance | 2007-07-23 19:09:46 |
| 14 | Oracle | 32 | 15 | 12 | Classical | General | 2007-07-23 19:09:46 |
| 15 | Pl/SQL | 20 | 10 | 5 | Classical | Opera | 2007-07-23 19:09:46 |
| 16 | Sql Server | 23 | 12 | 8 | Classical | General | 2007-07-23 19:09:46 |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
16 rows in set (0.00 sec)
mysql>
mysql>
mysql> SELECT Name, Department, Category
-> FROM Topic
-> WHERE Category IS NOT NULL
-> ORDER BY Name;
+----------------+------------+----------+
| Name | Department | Category |
+----------------+------------+----------+
| ASP.net | Popular | Country |
| C | Classical | Dance |
| C Sharp | Popular | Jazz |
| C++ | Classical | General |
| Java | Popular | Rock |
| JavaScript | Classical | Opera |
| Oracle | Classical | General |
| Perl | Classical | Vocal |
| Php | Popular | Jazz |
| Pl/SQL | Classical | Opera |
| Python | Popular | Blues |
| Sql Server | Classical | General |
| UML | Classical | General |
| VB.net | Popular | New Age |
| VC.net | Popular | New Age |
| www.sqle.ru | Classical | Dance |
+----------------+------------+----------+
16 rows in set (0.00 sec)
mysql>
mysql> drop table Topic;
Query OK, 0 rows affected (0.00 sec)</source>

== IS NULL==



<source lang="sql">
mysql> CREATE TABLE Topic(
-> TopicID SMALLINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> Name VARCHAR(50) NOT NULL,
-> InStock SMALLINT UNSIGNED NOT NULL,
-> OnOrder SMALLINT UNSIGNED NOT NULL,
-> Reserved SMALLINT UNSIGNED NOT NULL,
-> Department ENUM("Classical", "Popular") NOT NULL,
-> Category VARCHAR(20) NOT NULL,
-> RowUpdate TIMESTAMP NOT NULL
-> );
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql>
mysql> INSERT INTO Topic (Name, InStock, OnOrder, Reserved, Department, Category) VALUES
-> ("Java", 10, 5, 3, "Popular", "Rock"),
-> ("JavaScript", 10, 5, 3, "Classical", "Opera"),
-> ("C Sharp", 17, 4, 1, "Popular", "Jazz"),
-> ("C", 9, 4, 2, "Classical", "Dance"),
-> ("C++", 24, 2, 5, "Classical", "General"),
-> ("Perl", 16, 6, 8, "Classical", "Vocal"),
-> ("Python", 2, 25, 6, "Popular", "Blues"),
-> ("Php", 32, 3, 10, "Popular", "Jazz"),
-> ("ASP.net", 12, 15, 13, "Popular", "Country"),
-> ("VB.net", 5, 20, 10, "Popular", "New Age"),
-> ("VC.net", 24, 11, 14, "Popular", "New Age"),
-> ("UML", 42, 17, 17, "Classical", "General"),
-> ("www.sqle.ru",25, 44, 28, "Classical", "Dance"),
-> ("Oracle", 32, 15, 12, "Classical", "General"),
-> ("Pl/SQL", 20, 10, 5, "Classical", "Opera"),
-> ("Sql Server", 23, 12, 8, "Classical", "General");
Query OK, 16 rows affected (0.01 sec)
Records: 16 Duplicates: 0 Warnings: 0
mysql>
mysql> select * from Topic;
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| TopicID | Name | InStock | OnOrder | Reserved | Department | Category | RowUpdate |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| 1 | Java | 10 | 5 | 3 | Popular | Rock | 2007-07-23 19:09:46 |
| 2 | JavaScript | 10 | 5 | 3 | Classical | Opera | 2007-07-23 19:09:46 |
| 3 | C Sharp | 17 | 4 | 1 | Popular | Jazz | 2007-07-23 19:09:46 |
| 4 | C | 9 | 4 | 2 | Classical | Dance | 2007-07-23 19:09:46 |
| 5 | C++ | 24 | 2 | 5 | Classical | General | 2007-07-23 19:09:46 |
| 6 | Perl | 16 | 6 | 8 | Classical | Vocal | 2007-07-23 19:09:46 |
| 7 | Python | 2 | 25 | 6 | Popular | Blues | 2007-07-23 19:09:46 |
| 8 | Php | 32 | 3 | 10 | Popular | Jazz | 2007-07-23 19:09:46 |
| 9 | ASP.net | 12 | 15 | 13 | Popular | Country | 2007-07-23 19:09:46 |
| 10 | VB.net | 5 | 20 | 10 | Popular | New Age | 2007-07-23 19:09:46 |
| 11 | VC.net | 24 | 11 | 14 | Popular | New Age | 2007-07-23 19:09:46 |
| 12 | UML | 42 | 17 | 17 | Classical | General | 2007-07-23 19:09:46 |
| 13 | www.sqle.ru | 25 | 44 | 28 | Classical | Dance | 2007-07-23 19:09:46 |
| 14 | Oracle | 32 | 15 | 12 | Classical | General | 2007-07-23 19:09:46 |
| 15 | Pl/SQL | 20 | 10 | 5 | Classical | Opera | 2007-07-23 19:09:46 |
| 16 | Sql Server | 23 | 12 | 8 | Classical | General | 2007-07-23 19:09:46 |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
16 rows in set (0.00 sec)
mysql>
mysql> SELECT Name, Department, Category
-> FROM Topic
-> WHERE Category IS NULL
-> ORDER BY Name;
Empty set (0.00 sec)
mysql>
mysql> drop table Topic;
Query OK, 0 rows affected (0.00 sec)</source>

== Is NULL or = NULL==



<source lang="sql">
mysql>
mysql> CREATE TABLE Topic(
-> TopicID SMALLINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> Name VARCHAR(50) NOT NULL,
-> InStock SMALLINT UNSIGNED NOT NULL,
-> OnOrder SMALLINT UNSIGNED NOT NULL,
-> Reserved SMALLINT UNSIGNED NOT NULL,
-> Department ENUM("Classical", "Popular") NOT NULL,
-> Category VARCHAR(20) NOT NULL,
-> RowUpdate TIMESTAMP NOT NULL
-> );
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql>
mysql> INSERT INTO Topic (Name, InStock, OnOrder, Reserved, Department, Category) VALUES
-> ("Java", 10, 5, 3, "Popular", "Rock"),
-> ("JavaScript", 10, 5, 3, "Classical", "Opera"),
-> ("C Sharp", 17, 4, 1, "Popular", "Jazz"),
-> ("C", 9, 4, 2, "Classical", "Dance"),
-> ("C++", 24, 2, 5, "Classical", "General"),
-> ("Perl", 16, 6, 8, "Classical", "Vocal"),
-> ("Python", 2, 25, 6, "Popular", "Blues"),
-> ("Php", 32, 3, 10, "Popular", "Jazz"),
-> ("ASP.net", 12, 15, 13, "Popular", "Country"),
-> ("VB.net", 5, 20, 10, "Popular", "New Age"),
-> ("VC.net", 24, 11, 14, "Popular", "New Age"),
-> ("UML", 42, 17, 17, "Classical", "General"),
-> ("www.sqle.ru",25, 44, 28, "Classical", "Dance"),
-> ("Oracle", 32, 15, 12, "Classical", "General"),
-> ("Pl/SQL", 20, 10, 5, "Classical", "Opera"),
-> ("Sql Server", 23, 12, 8, "Classical", "General");
Query OK, 16 rows affected (0.00 sec)
Records: 16 Duplicates: 0 Warnings: 0
mysql>
mysql> select * from Topic;
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| TopicID | Name | InStock | OnOrder | Reserved | Department | Category | RowUpdate |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| 1 | Java | 10 | 5 | 3 | Popular | Rock | 2007-07-23 19:09:45 |
| 2 | JavaScript | 10 | 5 | 3 | Classical | Opera | 2007-07-23 19:09:45 |
| 3 | C Sharp | 17 | 4 | 1 | Popular | Jazz | 2007-07-23 19:09:45 |
| 4 | C | 9 | 4 | 2 | Classical | Dance | 2007-07-23 19:09:45 |
| 5 | C++ | 24 | 2 | 5 | Classical | General | 2007-07-23 19:09:45 |
| 6 | Perl | 16 | 6 | 8 | Classical | Vocal | 2007-07-23 19:09:45 |
| 7 | Python | 2 | 25 | 6 | Popular | Blues | 2007-07-23 19:09:45 |
| 8 | Php | 32 | 3 | 10 | Popular | Jazz | 2007-07-23 19:09:45 |
| 9 | ASP.net | 12 | 15 | 13 | Popular | Country | 2007-07-23 19:09:45 |
| 10 | VB.net | 5 | 20 | 10 | Popular | New Age | 2007-07-23 19:09:45 |
| 11 | VC.net | 24 | 11 | 14 | Popular | New Age | 2007-07-23 19:09:45 |
| 12 | UML | 42 | 17 | 17 | Classical | General | 2007-07-23 19:09:45 |
| 13 | www.sqle.ru | 25 | 44 | 28 | Classical | Dance | 2007-07-23 19:09:45 |
| 14 | Oracle | 32 | 15 | 12 | Classical | General | 2007-07-23 19:09:45 |
| 15 | Pl/SQL | 20 | 10 | 5 | Classical | Opera | 2007-07-23 19:09:45 |
| 16 | Sql Server | 23 | 12 | 8 | Classical | General | 2007-07-23 19:09:45 |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
16 rows in set (0.00 sec)
mysql>
mysql>
mysql> SELECT Name, Department, Category
-> FROM Topic
-> WHERE Category is NULL
-> ORDER BY Name;
Empty set (0.00 sec)
mysql>
mysql>
mysql>
mysql> SELECT Name, Department, Category
-> FROM Topic
-> WHERE Category = NULL
-> ORDER BY Name;
Empty set (0.00 sec)
mysql>
mysql>
mysql> drop table Topic;
Query OK, 0 rows affected (0.00 sec)</source>

== <=>NULL: NULL safe comparison==



<source lang="sql">
mysql>
mysql> CREATE TABLE Topic(
-> TopicID SMALLINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> Name VARCHAR(50) NOT NULL,
-> InStock SMALLINT UNSIGNED NOT NULL,
-> OnOrder SMALLINT UNSIGNED NOT NULL,
-> Reserved SMALLINT UNSIGNED NOT NULL,
-> Department ENUM("Classical", "Popular") NOT NULL,
-> Category VARCHAR(20) NOT NULL,
-> RowUpdate TIMESTAMP NOT NULL
-> );
Query OK, 0 rows affected (0.03 sec)
mysql>
mysql>
mysql> INSERT INTO Topic (Name, InStock, OnOrder, Reserved, Department, Category) VALUES
-> ("Java", 10, 5, 3, "Popular", "Rock"),
-> ("JavaScript", 10, 5, 3, "Classical", "Opera"),
-> ("C Sharp", 17, 4, 1, "Popular", "Jazz"),
-> ("C", 9, 4, 2, "Classical", "Dance"),
-> ("C++", 24, 2, 5, "Classical", "General"),
-> ("Perl", 16, 6, 8, "Classical", "Vocal"),
-> ("Python", 2, 25, 6, "Popular", "Blues"),
-> ("Php", 32, 3, 10, "Popular", "Jazz"),
-> ("ASP.net", 12, 15, 13, "Popular", "Country"),
-> ("VB.net", 5, 20, 10, "Popular", "New Age"),
-> ("VC.net", 24, 11, 14, "Popular", "New Age"),
-> ("UML", 42, 17, 17, "Classical", "General"),
-> ("www.sqle.ru",25, 44, 28, "Classical", "Dance"),
-> ("Oracle", 32, 15, 12, "Classical", "General"),
-> ("Pl/SQL", 20, 10, 5, "Classical", "Opera"),
-> ("Sql Server", 23, 12, 8, "Classical", "General");
Query OK, 16 rows affected (0.00 sec)
Records: 16 Duplicates: 0 Warnings: 0
mysql>
mysql> select * from Topic;
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| TopicID | Name | InStock | OnOrder | Reserved | Department | Category | RowUpdate |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
| 1 | Java | 10 | 5 | 3 | Popular | Rock | 2007-07-23 19:09:46 |
| 2 | JavaScript | 10 | 5 | 3 | Classical | Opera | 2007-07-23 19:09:46 |
| 3 | C Sharp | 17 | 4 | 1 | Popular | Jazz | 2007-07-23 19:09:46 |
| 4 | C | 9 | 4 | 2 | Classical | Dance | 2007-07-23 19:09:46 |
| 5 | C++ | 24 | 2 | 5 | Classical | General | 2007-07-23 19:09:46 |
| 6 | Perl | 16 | 6 | 8 | Classical | Vocal | 2007-07-23 19:09:46 |
| 7 | Python | 2 | 25 | 6 | Popular | Blues | 2007-07-23 19:09:46 |
| 8 | Php | 32 | 3 | 10 | Popular | Jazz | 2007-07-23 19:09:46 |
| 9 | ASP.net | 12 | 15 | 13 | Popular | Country | 2007-07-23 19:09:46 |
| 10 | VB.net | 5 | 20 | 10 | Popular | New Age | 2007-07-23 19:09:46 |
| 11 | VC.net | 24 | 11 | 14 | Popular | New Age | 2007-07-23 19:09:46 |
| 12 | UML | 42 | 17 | 17 | Classical | General | 2007-07-23 19:09:46 |
| 13 | www.sqle.ru | 25 | 44 | 28 | Classical | Dance | 2007-07-23 19:09:46 |
| 14 | Oracle | 32 | 15 | 12 | Classical | General | 2007-07-23 19:09:46 |
| 15 | Pl/SQL | 20 | 10 | 5 | Classical | Opera | 2007-07-23 19:09:46 |
| 16 | Sql Server | 23 | 12 | 8 | Classical | General | 2007-07-23 19:09:46 |
+---------+----------------+---------+---------+----------+------------+----------+---------------------+
16 rows in set (0.00 sec)
mysql>
mysql> SELECT Name, Department, Category
-> FROM Topic
-> WHERE Category<=>NULL
-> ORDER BY Name;
Empty set (0.00 sec)
mysql>
mysql> drop table Topic;
Query OK, 0 rows affected (0.02 sec)</source>

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