Summary: in this tutorial, we will show you various PostgreSQL length functions that return the number of characters or the number of bytes of a string.
PostgreSQL LENGTH function
The following illustrates the syntax of the length function:
1 | LENGTH(string); |
The length function accepts a string as a parameter. A string can be any of the following data types:
- character or char
- character varying or varchar
- text
The length function returns the number of characters in the string.
PostgreSQL length function examples
See the following example of using the length function:
1 2 | SELECT LENGTH ('PostgreSQL Tutorial'); -- 19 |
Notice that a string can hold an empty string, which is not a null value.
1 2 | SELECT LENGTH (''); -- 0 |
It returns zero. However, a string that holds a space character:
1 2 | SELECT LENGTH (' '); -- 1 |
It returns 1.
If you pass a NULL value to the length function, it returns a NULL value.
1 2 | SELECT LENGTH (NULL); -- NULL |
The following query gets the full names of customers in the customer table and uses the length function to get the number of characters in their names.
1 2 3 4 5 6 7 | SELECT first_name || ' ' || last_name AS name, LENGTH (first_name || ' ' || last_name) len FROM customer ORDER BY len; |
Sometimes, you may want to measure the length of a number instead of a string. In this case, you use type cast to convert the number into a string and use the length function as the following example:
1 2 | SELECT LENGTH (CAST(12345 AS TEXT)); --- 5 |
We often use the length function with other string functions such as replace, substring, etc., to manipulate string more efficiently. The following statement gets the user name and domain from the an email address using substring, strpos, and lengthfunctions.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | SELECT SUBSTRING ( 1, strpos( '@' ) - 1 ) AS user_name, SUBSTRING ( strpos( '@' ) + 1, LENGTH ( ) ) AS domain_name; |
Besides the length function, PostgreSQL provides the char_length and character_length functions that provide the same functionality.
Measure strings in bytes and bits
To get the number of bytes in a string, you use the octet_length function as follows:
1 | OCTET_LENGTH(string); |
See the following example:
1 2 | SELECT OCTET_LENGTH ('A'); -- 1 byte |
It returns 1 byte.
1 2 | SELECT OCTET_LENGTH ('€'); -- 3 bytes |
It returns 3 bytes. However, with the length function, it returns just 1.
1 2 | SELECT LENGTH ('€'); -- 1 |
To measure the number of bits of a string, you use the bit_length function as follows:
1 | BIT_LENGTH(string); |
See the following examples of using the bit_length function.
1 2 | SELECT BIT_LENGTH ('A'); -- 8 bits |
1 2 | SELECT BIT_LENGTH ('€'); -- 24 bits |
In this tutorial, we have shown you how to use length, bit_length, and octet_length functions to return the number of characters, the number of bits, and the number of bytes of a string.