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mysql 常用的3類函數(shù)
發(fā)表時間：2023-07-10 來源：明輝站整理相關(guān)軟件相關(guān)文章人氣：
[摘要]本篇文章主要介紹mysql 常用的三類函數(shù)，感興趣的朋友參考下，希望對大家有所幫助。一、字符串類。注：mysql在處理字符串時，字符下標(biāo)從1開始。1、concat(string1, string2,...
本篇文章主要介紹mysql 常用的三類函數(shù)，感興趣的朋友參考下，希望對大家有所幫助。一、字符串類。
注：mysql在處理字符串時，字符下標(biāo)從1開始。
1、concat(string1, string2, ......); //連接字符串
mysql> select concat('leng', 'xue', 'gang') as name;
+-------------+
name
+-------------+
lengxuegang
+-------------+
1 row in set (0.00 sec)
2、instr(string, substring); //返回substring首次在string中出現(xiàn)的位置，不存在返回0
mysql> select instr('lengxuegang', 'xue');
+-----------------------------+
instr('lengxuegang', 'xue')
+-----------------------------+
5
+-----------------------------+
1 row in set (0.00 sec)
mysql> select instr('lengxuegang', 'none');
+------------------------------+
instr('lengxuegang', 'none')
+------------------------------+
0
+------------------------------+
1 row in set (0.00 sec)
3、lcase(string); //轉(zhuǎn)換為小寫
mysql> select lcase('LengxueGang');
+----------------------+
lcase('LengxueGang')
+----------------------+
lengxuegang
+----------------------+
1 row in set (0.00 sec)
4、left(string, length); //從string左邊起取length個字符
mysql> select left('lengxuegang', 4);
+------------------------+
left('lengxuegang', 4)
+------------------------+
leng
+------------------------+
1 row in set (0.01 sec)
5、length(string); //返回string的長度
mysql> select length('lengxuegang');
+-----------------------+
length('lengxuegang')
+-----------------------+
11
+-----------------------+
1 row in set (0.25 sec)
6、locate(substring, string, [start_position]); //從start_position出開始查找，返回substring在string中首次出現(xiàn)的位置。其功能與instr類似，不過注意string與substring的位置是不一樣的。
mysql> select locate('leng', 'lengxueganglengxuegang', 4);
+---------------------------------------------+
locate('leng', 'lengxueganglengxuegang', 4)
+---------------------------------------------+
12
+---------------------------------------------+
1 row in set (0.00 sec)
7、ltrim(string); //去除左邊的空格
mysql> select ltrim(' leng');
+------------------+
ltrim(' leng')
+------------------+
leng
+------------------+
1 row in set (0.00 sec)
8、repeat(string, count); //重復(fù)string count次
mysql> select repeat('leng', 4);
+-------------------+
repeat('leng', 4)
+-------------------+
lenglenglengleng
+-------------------+
1 row in set (0.00 sec)
9、replace(string, search_str, replace_str); //在string中將search_str替換為replace_str
mysql> select replace('lengxueganglengxuegang', 'leng', 'cheng');
+----------------------------------------------------+
replace('lengxueganglengxuegang', 'leng', 'cheng')
+----------------------------------------------------+
chengxuegangchengxuegang
+----------------------------------------------------+
1 row in set (0.05 sec)
10、rtrim(string); //去除右端空格
mysql> select rtrim('leng ');
+--------------------+
rtrim('leng ')
+--------------------+
leng
+--------------------+
1 row in set (0.00 sec)
11、strcmp(string1， string2); //比較兩個字符串大小，按大小關(guān)系分別返回1、0、-1
mysql> select strcmp('leng', 'cheng');
+-------------------------+
strcmp('leng', 'cheng')
+-------------------------+
1
+-------------------------+
1 row in set (0.04 sec)
mysql> select strcmp('cheng', 'leng');
+-------------------------+
strcmp('cheng', 'leng')
+-------------------------+
-1
+-------------------------+
1 row in set (0.00 sec)
mysql> select strcmp('leng', 'leng');
+------------------------+
strcmp('leng', 'leng')
+------------------------+
0
+------------------------+
1 row in set (0.00 sec)
12、substring(string, start_pos, length); //從string的start_pos開始，取length個字符
mysql> select substring('lengxuegang', 5, 3);
+--------------------------------+
substring('lengxuegang', 5, 3)
+--------------------------------+
xue
+--------------------------------+
1 row in set (0.00 sec)
13、trim(); //去除字符串兩端空格
mysql> select trim(' leng ');
+-------------------+
trim(' leng ')
+-------------------+
leng
+-------------------+
1 row in set (0.00 sec)
14、ucase(string); //轉(zhuǎn)換為大寫
mysql> select ucase('lengxuegang');
+----------------------+
ucase('lengxuegang')
+----------------------+
LENGXUEGANG
+----------------------+
1 row in set (0.00 sec)
15、right(string, length); //取string右邊length個字符
mysql> select right('lengxuegang', 4);
+-------------------------+
right('lengxuegang', 4)
+-------------------------+
gang
+-------------------------+
1 row in set (0.00 sec)
16、space(count); //生成count個空格
mysql> select space(5);
+----------+
space(5)
+----------+
+----------+
1 row in set (0.00 sec)
17、lpad(string, length, pad); //在string的左端填充pad，直到其長度達(dá)到length
mysql> select lpad('leng', 10, 'dacb');
+--------------------------+
lpad('leng', 10, 'dacb')
+--------------------------+
dacbdaleng
+--------------------------+
1 row in set (0.00 sec)
18、rpad(); //在string的右端填充pad，直到其長度達(dá)到length
mysql> select rpad('leng', 10, 'dacb');
+--------------------------+
rpad('leng', 10, 'dacb')
+--------------------------+
lengdacbda
+--------------------------+
1 row in set (0.00 sec)
19、coalesce(value1, value2, ...) 返回第一個非null值，如果全為null，則返回null
mysql> select coalesce(null, 1, 2);
+----------------------+
coalesce(null, 1, 2)
+----------------------+
1
+----------------------+
1 row in set (0.03 sec)
二、數(shù)學(xué)類
1、abs(num); //返回絕對值
mysql> select abs(-3.5);
+-----------+
abs(-3.5)
+-----------+
3.5
+-----------+
1 row in set (0.03 sec)
2、bin(decimal_num); //十進(jìn)制轉(zhuǎn)二進(jìn)制
mysql> select bin(12);
+---------+
bin(12)
+---------+
1100
+---------+
1 row in set (0.05 sec)
3、ceiling(num); //向上取整
mysql> select ceiling(3.4);
+--------------+
ceiling(3.4)
+--------------+
4
+--------------+
1 row in set (0.00 sec)
mysql> select ceiling(-3.4);
+---------------+
ceiling(-3.4)
+---------------+
-3
+---------------+
1 row in set (0.00 sec)
4、conv(num, from_base, to_base); //進(jìn)制轉(zhuǎn)換
mysql> select conv(10, 10, 2);
+-----------------+
conv(10, 10, 2)
+-----------------+
1010
+-----------------+
1 row in set (0.00 sec)
5、floor(num); //向下取整
mysql> select floor(3.6);
+------------+
floor(3.6)
+------------+
3
+------------+
1 row in set (0.00 sec)
mysql> select floor(-3.6);
+-------------+
floor(-3.6)
+-------------+
-4
+-------------+
1 row in set (0.00 sec)
6、least(num1, num2, num3, ......); //取最小值
mysql> select least(10, 4, -4, 0);
+---------------------+
least(10, 4, -4, 0)
+---------------------+
-4
+---------------------+
1 row in set (0.10 sec)
7、mod(); //取余
mysql> select mod(10, 3);
+------------+
mod(10, 3)
+------------+
1
+------------+
1 row in set (0.00 sec)
8、power(num, power); //冪運(yùn)算
mysql> select power(3, 3);
+-------------+
power(3, 3)
+-------------+
27
+-------------+
1 row in set (0.08 sec)
9、rand([seed]); //隨機(jī)數(shù)
mysql> select rand();
+------------------+
rand()
+------------------+
0.10342728263086
+------------------+
1 row in set (0.00 sec)
mysql> select rand();
+------------------+
rand()
+------------------+
0.98467650821868
+------------------+
1 row in set (0.00 sec)
10、round(number, [decimals]); //四舍五入，decimals為小數(shù)位數(shù)
mysql> select round(1.2345);
+---------------+
round(1.2345)
+---------------+
1
+---------------+
1 row in set (0.00 sec)
mysql> select round(1.2345, 3);
+------------------+
round(1.2345, 3)
+------------------+
1.235
+------------------+
1 row in set (0.00 sec)
11、sign(number); //返回符號，正負(fù)或0
mysql> select sign(0);
+---------+
sign(0)
+---------+
0
+---------+
1 row in set (0.00 sec)
mysql> select sign(2);
+---------+
sign(2)
+---------+
1
+---------+
1 row in set (0.00 sec)
mysql> select sign(-2);
+----------+
sign(-2)
+----------+
-1
+----------+
1 row in set (0.00 sec)
12、sqrt(num); //開平方
mysql> select sqrt(3);
+-----------------+
sqrt(3)
+-----------------+
1.7320508075689
+-----------------+
1 row in set (0.00 sec)
13、greatest(value1, value2, ...); //取最大值
mysql> select greatest(2, 3, 10);
+--------------------+
greatest(2, 3, 10)
+--------------------+
10
+--------------------+
1 row in set (0.00 sec)
三、日期時間類
1、current_date(); //返回當(dāng)前日期
mysql> select current_date();
+----------------+
current_date()
+----------------+
2012-07-01
+----------------+
1 row in set (0.04 sec)
2、current_time(); //返回當(dāng)前時間
mysql> select current_time();
+----------------+
current_time()
+----------------+
02:05:41
+----------------+
1 row in set (0.00 sec)
3、current_timestamp(); //返回當(dāng)前時間戳
mysql> select current_timestamp();
+---------------------+
current_timestamp()
+---------------------+
2012-07-01 02:06:12
+---------------------+
1 row in set (0.04 sec)
4、now(); //返回當(dāng)前時間
mysql> select now();
+---------------------+
now()
+---------------------+
2012-07-01 02:06:57
+---------------------+
1 row in set (0.00 sec)
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