Просмотр исходного текста страницы MySQL Tutorial/Select Query/IS NULL

== IS NOT NULL==



   
  <!-- start source code -->
   
    <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==



   
  <!-- start source code -->
   
    <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==



   
  <!-- start source code -->
   
    <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==



   
  <!-- start source code -->
   
    <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>