語法順序：

select distinct 字段1，字段2，字段3 from 庫.表

　　where 條件　　　　

　　group by 分組條件　　

　　having 過濾　　　　# 執行順序的話，到這步會返回運行select語句，之後再運行order by

　　order by 排序字段

　　limit n；　　# 限制打印到屏幕上的條數

where 須在group by之前，不可用聚合函數

hanving需在group by之後，可用聚合函數

select 後面可以用聚合函數，如select count(id) from employee

執行順序：

from->where->group by->having->distinct->order by->limit

# group by

設置 mysql> set global sql_mode="ONLY_FULL_GROUP_BY";　　#select只能取分組的字段

select post from employee group by post;而不能select * from employee group by post;

# group_concat

把group by出來的記錄的某個字段值連起來，如 select post,group_concat(name) from employee group by post;

# having

select * from employee group by post having count(id)<2 ;

# order by

select * from employee order by age desc,id asc;

# limit

select * from employee limit 0,5;

select * from employee limit 5,5;　　# 分頁

sql語句之單表查詢