直接进入正题。

关键词：order、group、alter、count

1. 查询排序（order by）：

            正序（从小到大）：select * from [TableName] order by [FieldName];

                    示例：select * from testTable order by u_age;

            倒叙（从大到小）：select * from [TableName] order by [FieldName] desc;

                    示例：select * from testTable order by u_age desc;

2. 排序后，只显示最开始n条数据：

            select * from [TableName] order by [FieldName] limit n;

            示例①，正序(从小到大)：select * from testTable order by u_age limit 10;

            示例②，倒叙(从大到小)：select * from testTable order by u_age desc limit 10;

3. 查询分组（group by）：

            select * from [TableName] group by [FieldName] having [Term];

            示例：select * from testTable group by u_sex having u_class = "一班";

4. 设置数据库字段，字段内容用0补齐：

            create table [TableName] ([FieldName Type zerofill]);

            示例：create table testTable (u_number char(20) zerofill);

5. 修改表名：

            alter table [OldTableName] rename [NewTableName];

            示例：alter table class_u rename class_t;

6. 修改字段名：

            alter table [TableName] change [old_field_name] [new_field_name type];

            示例：alter table testTable change u_names u_name char(20);

7. 修改字段属性：

            alter table [TableName] modify [FieldName Type];

            示例：alter table testTable modify u_name char(20);

8. 查询结果统计（count）：

            select count(*) from [TableName] group by [FieldName] having [Term];

            示例：select count(*) from testTable group by c_name having c_name = '一班';

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