如何使用“ SHOW COLUMNS”作为表格的有效数据源？
为此，可以使用INFORMATION_SCHEMA.COLUMNS，如以下语法所示-
SELECT *FROM (SELECT *FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME= 'yourTableName') anyAliasName;
让我们首先创建一个表：
mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentFirstName varchar(20), StudentLastName varchar(20), StudentAge int );
这是使用`SHOWCOLUMNS`作为有效数据源的查询-
mysql> SELECT *FROM (SELECT *FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME= 'DemoTable')tbl;
这将产生以下输出-
+---------------+--------------+-------------+------------------+------------------+----------------+-------------+-----------+--------------------------+------------------------+-------------------+---------------+--------------------+--------------------+-----------------+-------------+------------+----------------+---------------------------------+----------------+-----------------------+--------+ | TABLE_CATALOG | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | ORDINAL_POSITION | COLUMN_DEFAULT | IS_NULLABLE | DATA_TYPE | CHARACTER_MAXIMUM_LENGTH | CHARACTER_OCTET_LENGTH | NUMERIC_PRECISION | NUMERIC_SCALE | DATETIME_PRECISION | CHARACTER_SET_NAME | COLLATION_NAME | COLUMN_TYPE | COLUMN_KEY | EXTRA | PRIVILEGES | COLUMN_COMMENT | GENERATION_EXPRESSION | SRS_ID | +---------------+--------------+-------------+------------------+------------------+----------------+-------------+-----------+--------------------------+------------------------+-------------------+---------------+--------------------+--------------------+-----------------+-------------+------------+----------------+---------------------------------+----------------+-----------------------+--------+ | def | sample | DemoTable | StudentId | 1 | NULL | NO | int | NULL | NULL | 10 | 0 | NULL | NULL | NULL | int(11) | PRI | auto_increment | select,insert,update,references | | | NULL | | def | sample | DemoTable | StudentFirstName | 2 | NULL | YES | varchar | 20 | 60 | NULL | NULL | NULL | utf8 | utf8_general_ci | varchar(20) | | | select,insert,update,references | | | NULL | | def | sample | DemoTable | StudentLastName | 3 | NULL | YES | varchar | 20 | 60 | NULL | NULL | NULL | utf8 | utf8_general_ci | varchar(20) | | | select,insert,update,references | | | NULL | | def | sample | DemoTable | StudentAge | 4 | NULL | YES | int | NULL | NULL | 10 | 0 | NULL | NULL | NULL | int(11) | | | select,insert,update,references | | | NULL | +---------------+--------------+-------------+------------------+------------------+----------------+-------------+-----------+--------------------------+------------------------+-------------------+---------------+--------------------+--------------------+-----------------+-------------+------------+----------------+---------------------------------+----------------+-----------------------+--------+ 4 rows in set (0.00 sec)