mysql - SHOW 命令中的单列

Question

我正在使用它来获取我的主要索引列。

SHOW INDEX FROM `table` WHERE Key_name='PRIMARY'

它返回一个包含类型、column_name、Key_name 等的表。

我只想要Column_name专栏。

我试过了：

SHOW INDEX.Column_name FROM `table` WHERE Key_name='PRIMARY'

但它没有用。有任何想法吗？

Answer 1

要从 PRIMARY KEY （按顺序）获取所有列mydb.mytable，请运行以下命令：

SELECT column_name
FROM information_schema.statistics
WHERE table_schema='mydb'
AND table_name='mytable'
AND index_name='PRIMARY'
ORDER BY seq_in_index;

mytable要从当前数据库中的 PRIMARY KEY（按顺序）获取所有列，请运行以下命令：

SELECT column_name
FROM information_schema.statistics
WHERE table_schema=DATABASE()
AND table_name='mytable'
AND index_name='PRIMARY'
ORDER BY seq_in_index;

这是一个示例表：

mysql> show create table cacti.host_snmp_cache\G
*************************** 1. row ***************************
       Table: host_snmp_cache
Create Table: CREATE TABLE `host_snmp_cache` (
  `host_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
  `snmp_query_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
  `field_name` varchar(50) NOT NULL DEFAULT '',
  `field_value` varchar(255) DEFAULT NULL,
  `snmp_index` varchar(255) NOT NULL DEFAULT '',
  `oid` text NOT NULL,
  PRIMARY KEY (`host_id`,`snmp_query_id`,`field_name`,`snmp_index`),
  KEY `host_id` (`host_id`,`field_name`),
  KEY `snmp_index` (`snmp_index`),
  KEY `field_name` (`field_name`),
  KEY `field_value` (`field_value`),
  KEY `snmp_query_id` (`snmp_query_id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql>

注意 PRIMARY KEY 有 4 列

这是查询的执行：

mysql> SELECT column_name
    -> FROM information_schema.statistics
    -> WHERE table_schema='cacti'
    -> AND table_name='host_snmp_cache'
    -> AND index_name='PRIMARY'
    -> ORDER BY seq_in_index;
+---------------+
| column_name   |
+---------------+
| host_id       |
| snmp_query_id |
| field_name    |
| snmp_index    |
+---------------+
4 rows in set (0.00 sec)

mysql>

使用GROUP_CONCAT，您可以将列名收集到 CSV 列表中

mysql> SELECT GROUP_CONCAT(column_name) PrimaryKeyColumns
    -> FROM information_schema.statistics
    -> WHERE table_schema='cacti'
    -> AND table_name='host_snmp_cache'
    -> AND index_name='PRIMARY'
    -> ORDER BY seq_in_index;
+---------------------------------------------+
| PrimaryKeyColumns                           |
+---------------------------------------------+
| host_id,snmp_query_id,field_name,snmp_index |
+---------------------------------------------+
1 row in set (0.01 sec)

mysql>

试试看 ！！！