Question

我的服务器上有两个不同名称的数据库，但两者都有一个标题为Clients的表。当我运行信息模式查询时，它会从两个数据库中返回列，所以当我只想要一个时，我会得到重复项。

示例：

SELECT COLUMN_NAME FROM information_schema.COLUMNS
WHERE table_name = 'Clients'

我收到了重复的列，因此First_Name出现了两次，因为它返回了两个数据库中Clients表的列。

我的问题是：

有没有办法在SELECT语句中指定要查询的数据库，以便它只返回我想要的列？例如：

SELECT COLUMN_NAME FROM information_schema.COLUMNS
WHERE db_name = 'DB1' AND table_name = 'Clients'

Answer 1

您正在寻找TABLE_SCHEMA列。

SELECT COLUMN_NAME 
FROM INFORMATION_SCHEMA.COLUMNS 
WHERE 
    TABLE_SCHEMA = 'DB1' AND 
    TABLE_NAME = 'Clients'

正如我所做的那样，这是我desc INFORMATION_SCHEMA.COLUMNS;

时得到的结果

+--------------------------+---------------------+------+-----+---------+-------+
| Field                    | Type                | Null | Key | Default | Extra |
+--------------------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG            | varchar(512)        | NO   |     |         |       |
| TABLE_SCHEMA             | varchar(64)         | NO   |     |         |       |
| TABLE_NAME               | varchar(64)         | NO   |     |         |       |
| COLUMN_NAME              | varchar(64)         | NO   |     |         |       |
| ORDINAL_POSITION         | bigint(21) unsigned | NO   |     | 0       |       |
| COLUMN_DEFAULT           | longtext            | YES  |     | NULL    |       |
| IS_NULLABLE              | varchar(3)          | NO   |     |         |       |
| DATA_TYPE                | varchar(64)         | NO   |     |         |       |
| CHARACTER_MAXIMUM_LENGTH | bigint(21) unsigned | YES  |     | NULL    |       |
| CHARACTER_OCTET_LENGTH   | bigint(21) unsigned | YES  |     | NULL    |       |
| NUMERIC_PRECISION        | bigint(21) unsigned | YES  |     | NULL    |       |
| NUMERIC_SCALE            | bigint(21) unsigned | YES  |     | NULL    |       |
| DATETIME_PRECISION       | bigint(21) unsigned | YES  |     | NULL    |       |
| CHARACTER_SET_NAME       | varchar(32)         | YES  |     | NULL    |       |
| COLLATION_NAME           | varchar(32)         | YES  |     | NULL    |       |
| COLUMN_TYPE              | longtext            | NO   |     | NULL    |       |
| COLUMN_KEY               | varchar(3)          | NO   |     |         |       |
| EXTRA                    | varchar(30)         | NO   |     |         |       |
| PRIVILEGES               | varchar(80)         | NO   |     |         |       |
| COLUMN_COMMENT           | varchar(1024)       | NO   |     |         |       |
| GENERATION_EXPRESSION    | longtext            | NO   |     | NULL    |       |
+--------------------------+---------------------+------+-----+---------+-------+

信息模式重复 - 指定要在SELECT中查询的数据库

1 个答案: