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# PostgreSQL LN() Function

**Summary**: in this tutorial, you will learn how to use the PostgreSQL `LN()` function to calculate the natural logarithm of a number.

## Introduction to the PostgreSQL LN() function

The natural logarithm is a function that represents the logarithm to base e, where e is Euler's number, which is approximately equal to `2.71828`.

In Math, the natural logarithm of a x is denoted as ln(x).

If ln(x) = y, then ey = x.

In PostgreSQL, you use the `LN()` function to calculate the natural logarithm of a number.

Here's the syntax of the `LN()` function:

```sql
LN(n)
```

In this syntax:

- `n` is a number with the type numeric or double precision. It can be a literal number, an expression, or a table column. `n` cannot be zero.

The `LN()` function returns the natural logarithm of `n` with the type corresponding to the type of `n`. It returns `NULL` if n is `NULL`.

If n is a string, the `LN()` function will convert it to a type numeric or double precision value. If the conversion fails, the `LN()` function raises an error.

The `LN()` function is the inverse of the [`EXP()`](https://neon.com/postgresql/postgresql-math-functions/postgresql-exp) function that returns the exponential value of a number.

## PostgreSQL LN() function examples

Let's take some examples of using the `LN()` function.

### 1) Basic PostgreSQL LN() function examples

The following example uses the `LN()` function to return the natural logarithm of 10:

```sql
SELECT LN(10) result;
```

Output:

```text
      result
-------------------
 2.302585092994046
```

The following statement uses the `LN()` function to return the natural logarithm of e:

```sql
SELECT LN(EXP(1)) result;
```

Output:

```text
 result
--------
      1
```

In this example, the `EXP`(1) function returns e1, which is e. Then, the `LN()` function returns the natural logarithm of e, which returns 1.

### 2) Using the LN() function with text

The following example uses the `LN()` function to calculate the natural logarithm of a numeric string '10'

```sql
SELECT LN('10') result;
```

Output:

```text
      result
-------------------
 2.302585092994046
```

In this example, the `LN()` function converts the string '10' to a number before calculating the natural logarithm.

The following example attempts to calculate the natural logarithm of the string '10x':

```sql
SELECT LN('10x') result;
```

The function raises an error because it cannot convert the string '10x' to a number:

```
ERROR:  invalid input syntax for type double precision: "10x"
LINE 1: SELECT LN('10x') result;
                  ^
```

## Summary

- Use the `LN()` function to calculate the natural logarithm of a number.

---

## Related docs (Math Functions)

- [ABS](https://neon.com/postgresql/postgresql-math-functions/postgresql-abs)
- [CBRT](https://neon.com/postgresql/postgresql-math-functions/postgresql-cbrt)
- [CEIL](https://neon.com/postgresql/postgresql-math-functions/postgresql-ceil)
- [DEGREES](https://neon.com/postgresql/postgresql-math-functions/postgresql-degrees)
- [DIV](https://neon.com/postgresql/postgresql-math-functions/postgresql-div)
- [EXP](https://neon.com/postgresql/postgresql-math-functions/postgresql-exp)
- [FACTORIAL](https://neon.com/postgresql/postgresql-math-functions/postgresql-factorial)
- [FLOOR](https://neon.com/postgresql/postgresql-math-functions/postgresql-floor)
- [GCD](https://neon.com/postgresql/postgresql-math-functions/postgresql-gcd)
- [LCM](https://neon.com/postgresql/postgresql-math-functions/postgresql-lcm)
- [LOG](https://neon.com/postgresql/postgresql-math-functions/postgresql-log)
- [MOD](https://neon.com/postgresql/postgresql-math-functions/postgresql-mod)
- [MIN_SCALE](https://neon.com/postgresql/postgresql-math-functions/postgresql-min_scale)
- [PI](https://neon.com/postgresql/postgresql-math-functions/postgresql-pi-function)
- [POWER](https://neon.com/postgresql/postgresql-math-functions/postgresql-power)
- [RADIANS](https://neon.com/postgresql/postgresql-math-functions/postgresql-radians)
- [RANDOM](https://neon.com/postgresql/postgresql-math-functions/postgresql-random)
- [ROUND](https://neon.com/postgresql/postgresql-math-functions/postgresql-round)
- [SCALE](https://neon.com/postgresql/postgresql-math-functions/postgresql-scale)
- [SIGN](https://neon.com/postgresql/postgresql-math-functions/postgresql-sign)
- [SQRT](https://neon.com/postgresql/postgresql-math-functions/postgresql-sqrt)
- [TRIM_SCALE](https://neon.com/postgresql/postgresql-math-functions/postgresql-trim_scale)
- [TRUNC](https://neon.com/postgresql/postgresql-math-functions/postgresql-trunc)
- [WIDTH_BUCKET](https://neon.com/postgresql/postgresql-math-functions/postgresql-width_bucket)