MySQL built-in functions

mysql Built in functions in

• String function
• Mathematical functions
• Date time function
• Type conversion function
• Process control
  

String function

• Look at the ascii Code value ascii(str), str Return when empty string 0
  
• see ascii The character corresponding to the code value char( Numbers )
  
• String concatenation concat(str1,str2…)
  
• Contains the number of characters length(str)
  
• Intercepting string
  • left(str, len) Return string str Left side len Characters
    
  • right(str,len) Return string str Right side len Characters
    
  • substring(str,pos,len) Return string str The location of pos rise len Characters
    
• Remove the space
  • ltrim(str) Returns the string with the left space removed str
    
  • rtrim(str) Returns the string with the right space removed str
    
• trim([ Direction remstr from str) Return to delete... From one side remstr String after str, Direction words include both、leading、trailing, On both sides 、 Left 、 Right
  
• Return from n A string of space characters space(n)
  
• Replace string replace(str,from_str,to_str)
  
• toggle case ,lower(str)、upper(str)
  

Mathematical functions

• Find the absolute value abs(n)
  
• seek m Divide n The remainder of mod(m,n), Same as operator %
  
  
• The floor ( Rounding down )floor(n), No greater than n Maximum integer for
  
  
• The ceiling ( Rounding up )ceiling(n), Not less than n Maximum integer for
  
  
• To find a rounding value round(n,d),n Means the original number ,d For decimal places , The default is 0
  
  
• seek x Of y The next power pow(x,y)
  
• Get the pi PI()
  
• random number rand(), The value is 0-1.0 Floating point number
  
• There are also many trigonometric functions , You can query documents when using

Date time function

• Get child value , Value is positive type , Function as follows ：
  • year(date) return date A year of ( The scope is 1000 To 9999)
  • month(date) return date Month value in
  • day(date) return date Date value in
  • hour(time) return time The number of hours ( The scope is 0 To 23)
  • minute(time) return time Minutes of ( The scope is 0 To 59)
  • second(time) return time The number of seconds ( The scope is 0 To 59)
    
• Date calculation , Use ± Operator , The keyword after the number is year、month、day、hour、minute、second
  
• Date formatting date_format(date,format)
  • Parameters format Optional value ：
    • %Y Year of acquisition , Return the full year
    • %y Year of acquisition , Returns the abbreviated year
    • %m Get the month , Return to the month
    • %d Acquisition date , Return day value
    • %H When getting , return 24 The number of hours in decimal
    • %h When getting , return 12 The number of hours in decimal
    • %i Get points , Return to minutes
    • %s Get seconds , Return seconds
      
• The current date current_date()
  
• current time current_time()
  
• Current date time now()
  

Small application

md5 encryption

• Be careful ： No matter what the length of the characters we want to encrypt , The length after encryption is 32 Bit fixed .md5 Encryption is irreversible ( According to the ciphertext, the plaintext cannot be decrypted )
  
  
  
  
  
  
  

sha1 encryption

• sha1 The encrypted length is 40 Bit
  
  
  
  
  

password() password