Database logic processing function

function

Numerical function

• abs(x) The absolute value
• ceil(x) Greater than or equal to x Minimum integer of
• floor(x) Less than or equal to x Maximum integer for
• mod(x,y) x Divide y The remainder of
• round(x,n) take x Round to n Decimal place
• rand() Returns a random number

Character functions

• char_length(s) Character length
• concat(a,b) Character connection
• instr(s,s1) Returns the first occurrence of a character , Case insensitive
• lower(a) / upper(b) Case conversion
• octet_length(s) The length of the returned character bytes ,utf-8 Character occupation 3 Characters
• substring(s,n,m) Intercept characters from n At the beginning m Letters , The position is calculated from 1 Start
• trim(s1 from s) Delete the beginning and end characters , Default is space

Date function

• current_date The current date
• current_time current time
• current_timestamp Current time and date
• extract(p from date) Extract information from dates
• datediff(d1, d2) Calculate the number of days between dates
• d1 + interval Date plus time interval

select date ‘2011-11-12’ + interval ‘-1’ month t_goodss

Conversion function

• cast

Alias

Both column names and table names use keywords AS

Conditional expression

case

case expression
 when value1 then result1
 when value2 then result2
 else --
 end

case 
 when conditon1 then result1
 when conditon2 then result2
 else --
 end

if

if and java The trinocular expression in is similar

select if(1<2, '1<2','1>=2') as result;