Knowledge points of MySQL (6)

One 、 Numerical function

1, Basic functions

Demonstration effect ： 

Code ：select abs(-12),sign(-23),sign(43),pi(),ceil(32.32),ceiling(-32.32),floor(43.43),floor(-43.43),mod(12,5) from dual;

rounding ：

mysql> select round(123,456),round(123.456,0),round(123.456,1),round(123.456,-1) from dual;

Truncation operation ：（ Whatever it is , Not at all ）
mysql> select truncate(123.456,0),truncate(123.456,1),truncate(129.45,-1) from dual;

 

 2, Trigonometric functions

Where angle and radian exchange function ：

 

 mysql> select radians(30),radians(45) from dual;

mysql> select degrees(2*pi()) from dual;（ Be careful PI Must be followed by parentheses ）

 

  Trigonometric functions ：
mysql> select sin(radians(30)),asin(0.5),degrees(asin(0.5)),tan(radians(45)) from dual;

 

3, Exponents and logarithms

 

logarithm ：

 mysql> select pow(2,5),power(2,4),exp(2) from dual;

Index （ The default is e）：

mysql> select ln(exp(2)),log(exp(2)),log10(10),log2(4) from dual;

 

 4, Conversion between bases

 mysql> select bin(10),hex(10),oct(10),conv(10,10,8) from dual;

 

Two 、 String function

 

 

  It should be noted that ：

When the string index is from 1 At the beginning ：
mysql> select insert('hellowworld',2,3,'aaaaa'),replace('helloword','l','mmm') from dual;

  3、 ... and 、 Date and time functions

1, Get date 、 The time of the

Get date and time ：

 mysql> select curdate(),current_date(),curtime(),now(),sysdate(),utc_date(),utc_time() from dual;

 2, Date and timestamp conversion

mysql> select unix_timestamp(),unix_timestamp('2022-7-04 12:12:30') from dual; 

 3, Get month 、 week 、 Weeks 、 Functions such as days

mysql> select year(curdate()),month(curdate()),day(curdate()),hour(curtime()),minute(now()),second(sysdate()) from dual; 

 4, Operation function of date

 mysql> select extract(second from now()),extract(month from now()) from dual;

 5, Time and second conversion function

 mysql>  select time_to_sec(curtime()),sec_to_time(45880) from dual;

6, Function for calculating date and time

The first group ：

  select now(), date_add(now(),interval 1 year), date_add(now(),interval -1 year),date_sub(now(),interval 1 year) from dual;

 

  The second group ：

5, Formatting and parsing of dates

format ： date ----> character string

analysis ： character string ----> date  

 

format （ Determine the case according to different situations ）：

 mysql> select date_format(curdate(),'%y-%m-%d'),date_format(now(),'%y-%m-%d') from dual;

mysql>  select date_format(curdate(),'%Y-%m-%d'),date_format(now(),'%Y-%m-%d') from dual;

  analysis ：（ The reverse of formatting ）：
mysql>  select str_to_date('2022-October-24th 11:34:42 Monday 1 ','%Y-%M-%D %h:%i:%S %W %w ') from dual;