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取字段注释
SELECT COLUMN_NAME 列名, DATA_TYPE 字段类型, COLUMN_COMMENT 字段注释
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'companies'##表名
AND table_schema = 'testhuicard'##数据库名
AND column_name LIKE 'c_name'##字段名
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例子：
SELECT COLUMN_COMMENT FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_name = 'admin'
AND table_schema = 'datas'
AND column_name LIKE 'name'
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SELECT table_name  表名,TABLE_COMMENT 表注释 FROM INFORMATION_SCHEMA.TABLES  WHERE table_schema = 'testhuicard' ##数据库名
AND table_name LIKE 'companies'##表名
参考http://dev.mysql.com/doc/refman/5.1/zh/information-schema.html.
mysql手册：23.1. INFORMATION_SCHEMA表

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