查询神通数据库某模式下基础元数据：表名、表注释、字段名、字段类型、字段长度

	SELECT
		a.TABLE_NAME,
		a.COLUMN_NAME,
		a.DATA_TYPE,
		IFNULL(CHAR_MAX_LENGTH,NUM_PREC) AS DATA_LENGTH,
		b.COMMENTS AS TABLE_COMMENTS,
		c.COMMENTS AS COLUMN_COMMENTS
	FROM
		(
			SELECT
				TABLE_NAME,
				COLUMN_NAME,
				DATA_TYPE,
				CHAR_MAX_LENGTH,
				CHAR_OCTET_LENGTH,
				NUM_PREC
			FROM
				INFO_SCHEM.COLUMNS
			WHERE
			-- 选取指定模式下的所有表
				TABLE_SCHEM = 'SYSDBA'
		) a
	LEFT JOIN INFO_SCHEM.ALL_TAB_COMMENTS b ON
		a.TABLE_NAME = b.TABLE_NAME
	LEFT JOIN INFO_SCHEM.ALL_COL_COMMENTS c ON
		c.COLUMN_NAME = a.COLUMN_NAME
		AND c.TABLE_NAME = a.TABLE_NAME