[3]This is an aggregate function and applies to the column x.
+  Addition 
  Subtraction (or unary minus) 
*  Multiplication 
/  Division 
**  Exponentiation 
abs(x)  Absolute value of x 
sqrt(x)  Square root of x 
exp(x)  e raised to the x 
log(x)  Natural log of x 
cos(x)  Cosine of x (x in radians) 
sin(x)  Sin of x (x in radians) 
atan(x)  Arc tangent of x (in radians) 
min(x,y)  Minimum of x and y 
max(x,y)  Maximum of x and y 
asin(x)  Arc sine of x (in radians) 
acos(x)  Arc cosine of x (in radians) 
cosh(x)  Hyperbolic cosine of x (x in radians) 
sech(x)  Hyperbolic cosecant of x (x in radians) 
pi  pi 
int4(x)  Integer truncation of x 
mod(x,y)  Remainder of x/y 
min(x)  Minimum of x 
max(x)  Maximum of x 
count(x)  Count of x 
countu(x)  Count of unique x 
sum(x)  Sum of x 
sumu(x)  Sum of unique x 
avg(x)  Average of x 
avgu(x)  Average of unique x 

Note: You can simulate the use of logical expressions (i.e. if then else) by using absolute value. For example, suppose that f is e_{1} if y is less than one and e_{2} if y is greater than one. Define an expression u = (abs(y1) /(y1) + 1)/2 and then define f = (1u) e_{1} + (u) e_{2}.
Note: Integer ratios are truncated in expression evaluation. If you ask for 20/100 to be retrieved the result is 0; if you ask for 20./100 the result is 0.2.