改变字段长度：
ALTER table schema.table_name ALTER column_name set data type VARCHAR(10);
call sysproc.admin_cmd('reorg table schema.table_name ');
call sysproc.admin_cmd('runstats on table schema.table_name with distribution and indexes all');
增加字段：
ALTER TABLE schema.table_name
ADD COLUMN column_name VARCHAR(100) NOT NULL WITH DEFAULT '*';
call sysproc.admin_cmd('reorg table schema.table_name ');
call sysproc.admin_cmd('runstats on table schema.table_name with distribution and indexes all');
加注释:
COMMENT ON COLUMN table_name.column_name IS '注释';
删除字段：
ALTER TABLE schema.table_name
DROP COLUMN column_name
