mysql所承建的所有表都保存在information_schema这个库里，而所有的字段都在columns 这张表里面，所以想查啥就去看对应的字段就行。
比如我想查询t_agent这张表里面所有的字段名、长度加类型、是否空，就可如下：

SELECT COLUMN_NAME AS '字段名', 
COLUMN_TYPE AS '长度加类型', 
IS_NULLABLE AS '空'
FROM information_schema.`COLUMNS`
WHERE TABLE_NAME LIKE 't_agent';

具体课查询的字段如下：

SELECT COLUMN_NAME AS '字段名'
FROM information_schema.`COLUMNS`
WHERE TABLE_NAME LIKE 'COLUMNS';

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

That’s all.