### Field Calculator

The field calculator allows you to update fields with expressions.

#### Supported Operations

Operation | Description
--- | ---
`column_name` `"column_name"` | value of field `column_name`
'`string`' | literal string value
`number` | number
NULL | null value
exp(`a`) | Euler's number e to the power of `a`
ln(`a`) | natural log (i.e. base e) of `a`
log10(`a`) | log base 10 of `a`
log(`a`,`b`) | log base `b` of `a`
sqrt(`a`) | square root
sin(`a`) | sine of `a`
cos(`a`) | cosine of `b`
tan(`a`) | tangent of `a`
asin(`a`) | inverse sine of `a`
acos(`a`) | inverse cosine of `a`
atan(`a`) | inverse tangent of `a`
to int(`a`) | convert string `a` to integer
to real(`a`) | convert string `a` to real
to string(`a`) | convert number `a` to string
lower(`a`) | convert string `a` to lower case
upper(`a`) | convert string `a` to upper case
length(`a`) | length of string `a`
atan2(`y`,`x`) | inverse tangent of `y`/`x` using the signs of the two arguments to determine the quadrant of the result.
replace(`a`,`replacethis`,`withthat`) | replace `replacethis` with `withthat` in string `a`
regexp_replace(`a`,`replacethis`,`withthat`) | replace the regular expression `replacethis` with `withthat` in string `a`
substr(`a`,`from`,`len`) | `len` characters of string `a` starting from `from` (first character index is 1)
`a` || `b` | concatenate strings `a` and `b`
$rownum | number current row
$area | area of polygon
$perimeter | perimeter of polygon
$length | area of line
$id | feature id
$x | x coordinate of point
$y | y coordinate of point
xat(`n`) | x coordinate of `n`th point of a line (indices start at 0; negative values apply to the last index)
yat(`n`) | y coordinate of `n`th point of a line (indices start at 0; negative values apply to the last index)
`a` ^ `b` | `a` raised to the power of `b`
`a` * `b` | `a` multiplied by `b`
`a` / `b` | `a` divided by `b`
`a` + `b` | `a` plus `b`
`a` - `b` | `a` minus `b`
+`a` | positive sign
-`a` | negative value of `a`