五、 order by 子句..........................................................................................................................12
5.1 语法和执行顺序.................................................................................................................12
5.2 升降序.................................................................................................................................12
5.3 null 值在排序中显示..........................................................................................................12
5.4 order by 后面可以跟什么..................................................................................................12
5.5 多列排序.............................................................................................................................12
六、 单行函数的使用....................................................................................................................13
6.1 数值类型.............................................................................................................................13
6.2 日期类型.............................................................................................................................13
6.3 字符类型.............................................................................................................................15
6.4 转换函数.............................................................................................................................16
6.5 其他注意事项.....................................................................................................................17
七、 SQL 语句中的分支................................................................................................................18
7.1 分支表达式.........................................................................................................................18
7.2 分支函数.............................................................................................................................18
八、 组函数.....................................................................................................................................19
8.1 报表统计常用.....................................................................................................................19
8.2 缺省情况组函数处理什么值.............................................................................................19
8.3 当组函数要处理的所有值都为 null 时.............................................................................19
8.4 行级信息和组级信息.........................................................................................................19
九、 group by 子句.........................................................................................................................21
9.1 语法和执行顺序.................................................................................................................21
9.2 分组过程.............................................................................................................................21
9.3 常见错误.............................................................................................................................21
9.4 多列分组.............................................................................................................................21
十、 having 子句.............................................................................................................................22
10.1 语法和执行顺序...............................................................................................................22
10.2 执行过程...........................................................................................................................22
10.3 where 和 having 区别........................................................................................................22
十一、 非关联子查询....................................................................................................................23
11.1 语法...................................................................................................................................23
11.2 子查询的执行过程...........................................................................................................23
11.3 常见错误...........................................................................................................................23
11.4 子查询与空值...................................................................................................................24
11.5 多列子查询.......................................................................................................................24
十二、 关联子查询........................................................................................................................25
12.1 语法...................................................................................................................................25
12.2 执行过程...........................................................................................................................25
12.3 exists..................................................................................................................................25
12.4 exists 执行过程.................................................................................................................25
12.5 not exists............................................................................................................................26
12.6 not exists 执行过程...........................................................................................................26
12.7 in 和 exists 比较................................................................................................................26
十三、 多表查询.............................................................................................................................27
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