[MySQL光速入門]010 運算符與函數

必會單詞

1. regexp 正則表達式
2. trim 修剪
3. replace 替換
4. ceiling 最高限度
5. year 年
6. month 月
7. day 日
8. hour 小時
9. minute 分鐘
10. second 秒
11. current 當前的
12. date 日期
13. time 時間
14. now 如今
15. week 星期
16. version 版本

運算符

算術運算符

• 加 +

  • select int類型的字段,int類型的字段+10 from 表;

  select bookprice,bookprice+10 from book;
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• 減 -

  • select int類型的字段,int類型的字段-10 from 表;

  select bookprice,bookprice-10 from book;
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• 乘 *

  • select int類型的字段,int類型的字段*10 from 表;

  select bookprice,bookprice*10 from book;
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• 除 /

  • select int類型的字段,int類型的字段/10 from 表;

  select bookprice,bookprice/10 from book;
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• 求餘/取模 %

  • select int類型的字段,int類型的字段%10 from 表;

  select bookprice,bookprice%10 from book;
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比較運算符

• 大於/小於

  • SELECT 字段1, 字段2 FROM 表 WHERE 字段2 > 值;

  SELECT bookname, bookprice FROM book WHERE bookprice > 20;
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  • SELECT 字段1, 字段2 FROM 表 WHERE 字段2 < 值;

  SELECT bookname, bookprice FROM book WHERE bookprice < 20;
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• 不等

  • SELECT 字段1, 字段2 FROM 表 WHERE 字段2 <> 值;

  SELECT bookname, bookprice FROM book WHERE bookprice <> 20;
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  • SELECT 字段1, 字段2 FROM 表 WHERE 字段2 != 值;

  SELECT bookname, bookprice FROM book WHERE bookprice != 20;
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• 正則

  • select 字段1,字段1 REGEXP '正則表達式1',字段2,字段2 REGEXP '正則表達式2',字段3,字段3 REGEXP '正則表達式3' from 表;

  select bookname,bookname REGEXP '^j',bookauthor,bookauthor REGEXP '紅$',bookpublisher,bookpublisher REGEXP '.+出版社' from book;
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  • select * from 表 where 字段 REGEXP '正則表達式';

  select * from book where bookpublisher REGEXP '.+[0-9]$';
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邏輯運算符

• && and

  • select * from 表名 where 字段 > 值1 and 字段 < 值2;

  select * from book where borrowsum > 5 and borrowsum < 30;
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  • select * from 表名 where 字段 > 值1 && 字段 < 值2;

  select * from book where borrowsum > 5 && borrowsum < 30;
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• ! not

  • select * from 表名 where not 字段名 = 值;

  select * from book where not borrowsum = 30;
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  • select * from 表名 where 字段名 != 值;

  select * from book where borrowsum != 30;
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  • select * from 表名 where 字段名 <> 值;

  select * from book where borrowsum <> 30;
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• || or

  • select * from 表名 where 字段 <= 值1 || 字段 >= 值2;

  select * from book where borrowsum <= 5 or borrowsum >= 30;
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  • select * from 表名 where 字段 <= 值1 or 字段 >= 值2;

  select * from book where borrowsum <= 5 || borrowsum >= 30;
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• 這四個語句, 結果同樣

  select * from book where borrowsum > 5 and borrowsum < 30;
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  select * from book where borrowsum > 5 && borrowsum < 30;
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  select * from book where not( borrowsum <= 5 or borrowsum >= 30);
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  select * from book where not( borrowsum <= 5 || borrowsum >= 30);
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內置函數

字符串函數

• left(s,n)/right(s,n)

  • select 字段,left(字段,2) from 表;

  select bookname,left(bookname,2) from book;
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  • select 字段,right(字段,2) from 表;

  select bookname,right(bookname,2) from book;
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• concat()/concat_ws()

  • select 字段1,字段2,字段3,字段4,字段5,CONCAT(字段1,字段2,字段3,字段4,字段5) as 別名1, CONCAT_WS('分隔符',字段1,字段2,字段3,字段4,字段5) as 別名2 from 表;

  select bookid,bookname,bookauthor,bookpublisher,bookprice,CONCAT(bookid,bookname,bookauthor,bookpublisher,bookprice) as 詳情1,CONCAT_WS('_',bookid,bookname,bookauthor,bookpublisher,bookprice) as 詳情2 from book;
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• trim()/ltrim(s)/rtrim(s)

  • select 字段, trim(字段) 別名1, ltrim(字段) 別名2, rtrim(字段) 別名3 from 表名;

  select bookpublisher,trim(bookpublisher) 刪除左右空格,ltrim(bookpublisher) 刪除左空格,rtrim(bookpublisher) 刪除右空格 from book;
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• replace()

  • select 字段 別名,replace(字段,'匹配的字段','替換的字段') 替換後 from 表名;

  select bookname 替換前,replace(bookname,'設計','崩潰') 替換後 from book;
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• substring()

  • select 字段, SUBSTRING(字段,開始位置從一開始,長度) from 表名;

  select bookname, SUBSTRING(bookname,2,3) from book;
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日期函數

• now()

  select now();
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• curdate()/curtime()

  select now(),CURRENT_DATE(),CURRENT_TIME(),curdate(),curtime();
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• dayofweek(d)/dayofmonth(d)/dayofyear(d)

  select now(),DAYOFWEEK(now()),DAYOFMONTH(now()),DAYOFYEAR(now()),WEEKDAY(now());
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• hour(t)/minute(t)/second(t)

  select now(),HOUR(now()),MINUTE(now()),SECOND(now());
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• date_add()/date_sub()

  select DATE_ADD(now(),interval 3 day);
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  select DATE_SUB(now(),INTERVAL 7 MINUTE);
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• datediff()

  select DATEDIFF('2020-10-1',now());
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數學函數

• abs(x)

  select abs(-789),abs(-123.666);
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• floor(x)/ceiling(x)

  select FLOOR(-2.3),CEILING(-2.3),FLOOR(9.9),CEILING(9.9);
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• greatest()/least()

  select GREATEST(1,2,3,4),LEAST(1,2,3,4);
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• round(x)/truncate(x,y)

  select round(3.4567),round(4.567),TRUNCATE(3.4567,3);
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• rand()

  select rand(),rand();
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• sqrt(x)/mod(x,y)

  select sqrt(64),sqrt(2),TRUNCATE(sqrt(2),3),mod(10,4);
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系統函數

• database()/user()/version()

  select DATABASE(),user(),version();
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• charset(str)/collation(str)

  select charset('123'),COLLATION('123');
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