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Sélectionnez les noms de colonnes dont les entrées ne sont pas nulles

Je voudrais avoir une liste de ces colonnes d'une table qui contiennent au moins une entrée de données non -NULL.

En d'autres termes, j'aimerais obtenir les noms de colonnes pour lesquels les éléments suivants renvoient au moins une entrée:

SELECT DISTINCT column_name FROM table WHERE column_name IS NOT NULL

J'ai essayé ce qui suit:

SELECT column_name
FROM information_schema.columns
WHERE table_name = "table_name"
AND EXISTS (
    SELECT DISTINCT column_name FROM table_name WHERE column_name IS NOT NULL
)

Mais cela renvoie également les noms des colonnes où toutes les entrées sont NULL.

Alors, comment puis-je obtenir uniquement les colonnes avec des entrées non -NULL?

mysqldatabase-designselectnull
7
Baz

Prenons un exemple de table sur ma machine:

mysql> show create table weisci_jaws_staging2.users\G
*************************** 1. row ***************************
       Table: users
Create Table: CREATE TABLE `users` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(32) NOT NULL DEFAULT '',
  `passwd` varchar(32) NOT NULL DEFAULT '',
  `user_type` tinyint(4) DEFAULT '2',
  `recovery_key` varchar(48) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `email` varchar(255) DEFAULT NULL,
  `url` varchar(255) DEFAULT NULL,
  `timezone` varchar(5) DEFAULT NULL,
  `language` varchar(5) DEFAULT NULL,
  `theme` varchar(24) DEFAULT NULL,
  `editor` varchar(24) DEFAULT NULL,
  `last_login` datetime DEFAULT NULL,
  `createtime` datetime DEFAULT NULL,
  `updatetime` datetime DEFAULT NULL,
  `change_passwd` tinyint(1) NOT NULL DEFAULT '1',
  `never_expire` tinyint(1) NOT NULL DEFAULT '1',
  `bad_passwd_count` smallint(6) DEFAULT '0',
  `last_access` bigint(20) DEFAULT '0',
  `enabled` tinyint(1) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`),
  UNIQUE KEY `users_username_idx` (`username`)
) ENGINE=MyISAM AUTO_INCREMENT=160 DEFAULT CHARSET=utf8
1 row in set (0.02 sec)

mysql> select count(1) from weisci_jaws_staging2.users;
+----------+
| count(1) |
+----------+
|      117 |
+----------+
1 row in set (0.00 sec)

mysql>

Avec ce tableau, voici deux questions:

  • Quelles colonnes peuvent être annulées?
  • Quelles colonnes ne peuvent pas être annulées?

Cette requête trouvera pour vous:

select is_nullable,GROUP_CONCAT(column_name) column_list
from information_schema.columns
where table_schema = 'weisci_jaws_staging2'
and   table_name = 'users'
group by is_nullable;

Découvrez le résultat de cette requête pour la table:

mysql> select is_nullable,GROUP_CONCAT(column_name) column_list
    -> from information_schema.columns
    -> where table_schema = 'weisci_jaws_staging2'
    -> and   table_name = 'users'
    -> group by is_nullable;
+-------------+------------------------------------------------------------------------------------------------------------------------------------+
| is_nullable | column_list                                                                                                                        |
+-------------+------------------------------------------------------------------------------------------------------------------------------------+
| NO          | id,never_expire,change_passwd,enabled,username,passwd                                                                              |
| YES         | recovery_key,last_access,bad_passwd_count,updatetime,createtime,last_login,editor,user_type,language,timezone,url,email,name,theme |
+-------------+------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.01 sec)

mysql>

OK, nous avons deux listes. Que retenons-nous de cela?

  • Si vous obtenez deux listes, pas besoin d'inspecter la table réelle car la table a par définition des colonnes non NULL.
  • Si vous obtenez une liste, alors
    • Si vous obtenez seulement is_nullable = 'NO', pas besoin d'inspecter la table réelle car la table a des colonnes non NULL par définition.
    • Si vous obtenez seulement is_nullable = 'YES', la table réelle serait un peu fragile. Il n'y aurait pas de CLÉ PRIMAIRE, pauvre âme tourmentée !!! MAINTENANT, vous devez recourir à la lecture de chaque ligne du tableau réel.

Si vous recherchez uniquement les colonnes non nulles, ce serait la requête souhaitée:

select GROUP_CONCAT(column_name) nonnull_columns
from information_schema.columns
where table_schema = 'weisci_jaws_staging2'
and   table_name = 'users'
and   is_nullable = 'NO';

Voici le résultat de cette requête:

mysql> select GROUP_CONCAT(column_name) nonnull_columns
    -> from information_schema.columns
    -> where table_schema = 'weisci_jaws_staging2'
    -> and   table_name = 'users'
    -> and   is_nullable = 'NO';
+-------------------------------------------------------+
| nonnull_columns                                       |
+-------------------------------------------------------+
| id,username,passwd,change_passwd,never_expire,enabled |
+-------------------------------------------------------+
1 row in set (0.01 sec)

mysql>

En supprimant le GROUP_CONCAT, vous obtenez ceci:

mysql> select column_name nonnull_column
    -> from information_schema.columns
    -> where table_schema = 'weisci_jaws_staging2'
    -> and   table_name = 'users'
    -> and   is_nullable = 'NO';
+----------------+
| nonnull_column |
+----------------+
| id             |
| username       |
| passwd         |
| change_passwd  |
| never_expire   |
| enabled        |
+----------------+
6 rows in set (0.01 sec)

mysql>

Essaie !!!

NOTE : veuillez noter que je n'ai pas besoin de lire le contenu réel des données du tableau. C'est beaucoup plus efficace que de lire la table entière.

MISE À JOUR 2012-11-15 13:40 EDT

Le code de la réponse de @ sensware donne NULL colonnes. La question d'origine demandait non-NULL Colonnes. J'ai augmenté le code pour tester uniquement ma table:

SET group_concat_max_len = 4294967295; -- to overcome default 1KB limitation
SELECT CONCAT(
         'SELECT * FROM ('
       ,  GROUP_CONCAT(
            CONCAT(
              'SELECT ', QUOTE(TABLE_NAME), ' AS `table`,'
            , 'IF('
            ,   'COUNT(`', REPLACE(COLUMN_NAME, '`', '``'), '`),'
            ,   'NULL,'
            ,    QUOTE(COLUMN_NAME)
            , ') AS `column` '
            , 'FROM `',
            REPLACE(TABLE_SCHEMA, '`', '``'), '`.`',
            REPLACE(TABLE_NAME, '`', '``'), '`'
            )
            SEPARATOR ' UNION ALL '
         )
       , ') t WHERE `column` IS NOT NULL'
       )
INTO   @sql
FROM   INFORMATION_SCHEMA.COLUMNS
WHERE  TABLE_SCHEMA = 'weisci_jaws_staging2'
AND    TABLE_NAME = 'users';
SELECT @sql\G
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Voici la sortie:

mysql> SET group_concat_max_len = 4294967295; -- to overcome default 1KB limitation
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT CONCAT(
    ->          'SELECT * FROM ('
    ->        ,  GROUP_CONCAT(
    ->             CONCAT(
    ->               'SELECT ', QUOTE(TABLE_NAME), ' AS `table`,'
    ->             , 'IF('
    ->             ,   'COUNT(`', REPLACE(COLUMN_NAME, '`', '``'), '`),'
    ->             ,   'NULL,'
    ->             ,    QUOTE(COLUMN_NAME)
    ->             , ') AS `column` '
    ->             , 'FROM `',
    ->             REPLACE(TABLE_SCHEMA, '`', '``'), '`.`',
    ->             REPLACE(TABLE_NAME, '`', '``'), '`'
    ->             )
    ->             SEPARATOR ' UNION ALL '
    ->          )
    ->        , ') t WHERE `column` IS NOT NULL'
    ->        )
    -> INTO   @sql
    -> FROM   INFORMATION_SCHEMA.COLUMNS
    -> WHERE  TABLE_SCHEMA = 'weisci_jaws_staging2'
    -> AND    TABLE_NAME = 'users';
Query OK, 1 row affected (0.02 sec)

mysql> SELECT @sql\G
*************************** 1. row ***************************
@sql: SELECT * FROM (SELECT 'users' AS `table`,IF(COUNT(`id`),NULL,'id') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`username`),NULL,'username') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`passwd`),NULL,'passwd') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`user_type`),NULL,'user_type') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`recovery_key`),NULL,'recovery_key') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`name`),NULL,'name') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`email`),NULL,'email') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`url`),NULL,'url') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`timezone`),NULL,'timezone') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`language`),NULL,'language') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`theme`),NULL,'theme') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`editor`),NULL,'editor') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`last_login`),NULL,'last_login') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`createtime`),NULL,'createtime') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`updatetime`),NULL,'updatetime') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`change_passwd`),NULL,'change_passwd') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`never_expire`),NULL,'never_expire') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`bad_passwd_count`),NULL,'bad_passwd_count') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`last_access`),NULL,'last_access') AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`enabled`),NULL,'enabled') AS `column` FROM `weisci_jaws_staging2`.`users`) t WHERE `column` IS NOT NULL
1 row in set (0.00 sec)

mysql> PREPARE stmt FROM @sql;
Query OK, 0 rows affected (0.01 sec)
Statement prepared

mysql> EXECUTE stmt;
+-------+--------+
| table | column |
+-------+--------+
| users | theme  |
+-------+--------+
1 row in set (0.00 sec)

mysql> DEALLOCATE PREPARE stmt;
Query OK, 0 rows affected (0.00 sec)

mysql>

Cela donne des colonnes NULL. La question d'origine demandait des colonnes non NULL. Je changerai le code en non-NULL généré. Je vais le faire en inversant l'ordre du IF..COUNT:

SET group_concat_max_len = 4294967295; -- to overcome default 1KB limitation
SELECT CONCAT(
         'SELECT * FROM ('
       ,  GROUP_CONCAT(
            CONCAT(
              'SELECT ', QUOTE(TABLE_NAME), ' AS `table`,'
            , 'IF('
            ,   'COUNT(`', REPLACE(COLUMN_NAME, '`', '``'), '`),'
            ,    QUOTE(COLUMN_NAME)
            ,   ',NULL'
            , ') AS `column` '
            , 'FROM `',
            REPLACE(TABLE_SCHEMA, '`', '``'), '`.`',
            REPLACE(TABLE_NAME, '`', '``'), '`'
            )
            SEPARATOR ' UNION ALL '
         )
       , ') t WHERE `column` IS NOT NULL'
       )
INTO   @sql
FROM   INFORMATION_SCHEMA.COLUMNS
WHERE  TABLE_SCHEMA = 'weisci_jaws_staging2'
AND    TABLE_NAME = 'users';
SELECT @sql\G
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Lançons-le maintenant ...

mysql> SET group_concat_max_len = 4294967295; -- to overcome default 1KB limitation
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT CONCAT(
    ->          'SELECT * FROM ('
    ->        ,  GROUP_CONCAT(
    ->             CONCAT(
    ->               'SELECT ', QUOTE(TABLE_NAME), ' AS `table`,'
    ->             , 'IF('
    ->             ,   'COUNT(`', REPLACE(COLUMN_NAME, '`', '``'), '`),'
    ->             ,    QUOTE(COLUMN_NAME)
    ->             ,   ',NULL'
    ->             , ') AS `column` '
    ->             , 'FROM `',
    ->             REPLACE(TABLE_SCHEMA, '`', '``'), '`.`',
    ->             REPLACE(TABLE_NAME, '`', '``'), '`'
    ->             )
    ->             SEPARATOR ' UNION ALL '
    ->          )
    ->        , ') t WHERE `column` IS NOT NULL'
    ->        )
    -> INTO   @sql
    -> FROM   INFORMATION_SCHEMA.COLUMNS
    -> WHERE  TABLE_SCHEMA = 'weisci_jaws_staging2'
    -> AND    TABLE_NAME = 'users';
Query OK, 1 row affected (0.01 sec)

mysql> SELECT @sql\G
*************************** 1. row ***************************
@sql: SELECT * FROM (SELECT 'users' AS `table`,IF(COUNT(`id`),'id',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`username`),'username',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`passwd`),'passwd',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`user_type`),'user_type',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`recovery_key`),'recovery_key',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`name`),'name',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`email`),'email',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`url`),'url',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`timezone`),'timezone',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`language`),'language',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`theme`),'theme',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`editor`),'editor',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`last_login`),'last_login',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`createtime`),'createtime',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`updatetime`),'updatetime',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`change_passwd`),'change_passwd',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`never_expire`),'never_expire',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`bad_passwd_count`),'bad_passwd_count',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`last_access`),'last_access',NULL) AS `column` FROM `weisci_jaws_staging2`.`users` UNION ALL SELECT 'users' AS `table`,IF(COUNT(`enabled`),'enabled',NULL) AS `column` FROM `weisci_jaws_staging2`.`users`) t WHERE `column` IS NOT NULL
1 row in set (0.00 sec)

mysql> PREPARE stmt FROM @sql;
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> EXECUTE stmt;
+-------+------------------+
| table | column           |
+-------+------------------+
| users | id               |
| users | username         |
| users | passwd           |
| users | user_type        |
| users | recovery_key     |
| users | name             |
| users | email            |
| users | url              |
| users | timezone         |
| users | language         |
| users | editor           |
| users | last_login       |
| users | createtime       |
| users | updatetime       |
| users | change_passwd    |
| users | never_expire     |
| users | bad_passwd_count |
| users | last_access      |
| users | enabled          |
+-------+------------------+
19 rows in set (0.01 sec)

mysql> DEALLOCATE PREPARE stmt;
Query OK, 0 rows affected (0.00 sec)

mysql>

OK ça marche maintenant. Un problème est toujours présent. La requête nécessite la lecture de la table entière. Ma table de test n'a que 117 lignes et 20 colonnes. Qu'en est-il des tables plus grandes avec des millions de lignes ou des dizaines de colonnes ? Je ne vais pas spéculer parce que je sais que le code serait pire de plusieurs ordres de grandeur.

Voilà pourquoi je recommande ma réponse

select GROUP_CONCAT(column_name) nonnull_columns
from information_schema.columns
where table_schema = 'weisci_jaws_staging2'
and   table_name = 'users'
and   is_nullable = 'NO';

ou

select column_name nonnull_column
from information_schema.columns
where table_schema = 'weisci_jaws_staging2'
and   table_name = 'users'
and   is_nullable = 'NO';

car le contenu réel des données n'a pas à être inspecté.

Le code augmenté que j'ai créé ne doit être utilisé que sur une table où toutes les colonnes autorisent les valeurs NULL, ce qui est extrêmement rare.

6
RolandoMySQLDBA

Je pense que cela a été répondu ici:

https://stackoverflow.com/questions/12091272/find-all-those-columns-which-have-only-null-values-in-a-mysql-table

Le code a été copié ci-dessous:

SET group_concat_max_len = 4294967295; -- to overcome default 1KB limitation

SELECT CONCAT(
         'SELECT * FROM ('
       ,  GROUP_CONCAT(
            CONCAT(
              'SELECT ', QUOTE(TABLE_NAME), ' AS `table`,'
            , 'IF('
            ,   'COUNT(`', REPLACE(COLUMN_NAME, '`', '``'), '`),'
            ,   'NULL,'
            ,    QUOTE(COLUMN_NAME)
            , ') AS `column` '
            , 'FROM `', REPLACE(TABLE_NAME, '`', '``'), '`'
            )
            SEPARATOR ' UNION ALL '
         )
       , ') t WHERE `column` IS NOT NULL'
       )
INTO   @sql
FROM   INFORMATION_SCHEMA.COLUMNS
WHERE  TABLE_SCHEMA = DATABASE();

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
3
sensware