PostgreSQL left() Function

The PostgreSQL left() function extracts the leftmost specified number of characters in the gaven string and returns them as a string.

If you want to extract a certain number of characters from the right of a string, use the right() function.

`left()` Syntax

This is the syntax of the PostgreSQL left() function:

left(str, num)

str: Required. The string where to extract characters.
num: Required. The number of characters to extract. It can be positive or negative. If it is negative, the left() function returns all characters except for the rightmost -num characters.

The PostgreSQL left() function returns the leftmost num characters of the string str.

If num is negative, the left() function returns all characters in the string except for the rightmost -num characters.

The left() function will return str if num is greater than the length of str.

If num equals 0, the left() function will return empty ''.

If the parameter is NULL, the function will return NULL.

This example shows how to use the left() function to get the leftmost 2 characters of the string hello.

SELECT left('hello', 2) AS "left('hello', 2)";

 left('hello', 2)
------------------
 he

You can provide a negative number for num:

SELECT left('hello', -3) AS "left('hello', -3)";

 left('hello', -3)
-------------------
 he

Here, since num is -3, the characters other than the rightmost 3 characters are returned. That is: he.