SUBSTR

Definition

The SUBSTR function allows you to extract a section of a longer string in BigQuery.

Practical Info

• SUBSTR works with STRING or BYTES data types
• The position argument is 1-based, so the first character is at position 1
• You can use -1 to indicate the last character position
• if length < 0 then the function returns an error

Common Questions

How to dynamically extract sub-strings?

SUBSTR(value, position[, length])

What if we have a series of email addresses: abc@gmail.com, xy@yahoo.com, etc. and we want to find the domain (e.g. gmail.com, yahoo.com), we can use SUBSTR in combination with STRPOS and LENGTH to dynamically extract everything after the @.

Alternatively, you can use REGEXP_EXTRACT to achieve the same result:

SELECT
  location,
  SUBSTR(location, (-2), 2) AS state
FROM
  (
    SELECT
      'New York, NY' AS location
    UNION ALL
(    SELECT
      'Miami, FL' AS location)
  ) AS table_2

Troubleshooting Common Errors

It's rare SUBSTR returns an error unless you call it with the wrong data types (e.g. pass a STRING to the position parameter), but it's often that you don't get what you want.

The best thing to do here is to either use REGEXP functions, or start get your query working with 1-2 example rows before trying to apply it to the entire column.

SELECT
  email,
  SUBSTR(email, (STRPOS(email, '@') + 1), (LENGTH(email) - STRPOS(email, '@'))) AS domain
FROM
  (
    SELECT
      'abc@gmail.com' AS email
    UNION ALL
(    SELECT
      'xy@yahoo.com' AS email)
  ) AS table_2

SELECT
  email,
  REGEXP_EXTRACT(email, r'@([a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$)') AS domain
FROM
  (
    SELECT
      'abc@gmail.com' AS email
    UNION ALL
(    SELECT
      'xy@yahoo.com' AS email)
  ) AS table_2