一、數學函式

1、求絕對值abs()

select abs(num) from tableName where ....

2、向下取整floor(),例如：99.9→99

select floor(num) from tableName where ...;

3、向上取整 ceil(),例如99.9→100

select ceil(num) from tableName where ...;

二、字串函式

1、新增資料insert(目標字串，下標，長度，追加內容)

select insert(name,2,3,hello) from tableName where ...;

解釋：對查詢結果從第二個字元，往後面擷取3個字元，把這三個字元替換為hello

2、upper() 將全部字串轉化為大寫

select upper(name) from tableName where ....;

3、lower() 將全部字串轉化為小寫

select lower(name) from tableName where ....;

4、left() 擷取字元:擷取前三個字元

select left(name,3) from tableName where ...;

5、right() 從後面擷取字元

6、substring(str,index,len) 擷取中間字元

select substring(name,2,4) from tableName where
 
 ...;

7、reverse() 逆序輸出字串

select reverse(name) from tableName where ...;