Regex Operations in BigQuery
Tags: regex, bigquery
Published: 2021-08-12 04:47:52

BigQuery is taking the analytics industry by a storm. One of the most important use-cases is to extract and transform parts of a string. Below are some of the powerful constructs provided by BigQuery.

Regex Constructs
----------------

BigQuery provides the following constructs for regex operations

| Construct | Arguments | Use |
| --- | --- | --- |
| [REGEXP_CONTAINS](https://cloud.google.com/bigquery/docs/reference/standard-sql/string_functions#regexp_contains) | `REGEXP_CONTAINS(value, regexp)` | Checks if the string contains the regex |
| [REGEXP_EXTRACT](https://cloud.google.com/bigquery/docs/reference/standard-sql/string_functions#regexp_extract) | `REGEXP_EXTRACT(value, regexp[, position[, occurrence]])` | Extract the substring that matches the regex. |
| [REGEXP_EXTRACT_ALL](https://cloud.google.com/bigquery/docs/reference/standard-sql/string_functions#regexp_extract_all) | `REGEXP_EXTRACT_ALL(value, regexp)` | Return all substrings that match the regex |
| [REGEXP_INSTR](https://cloud.google.com/bigquery/docs/reference/standard-sql/string_functions#regexp_instr) | `REGEXP_INSTR(source_value, regexp [, position[, occurrence, [occurrence_position]]])` | Return 1-based index for the first occurrence of the regex |
| [REGEXP_REPLACE] (https://cloud.google.com/bigquery/docs/reference/standard-sql/string_functions#regexp_replace) | `REGEXP_REPLACE(value, regexp, replacement)` | Replace all substrings in value |

Source : Google Cloud Platform
Table Setup
-------------

Let's create a simple table with some string data to play around.

```
-- Create Store
CREATE OR REPLACE TABLE `gcp-tour-276710.thefellowcoder.store`
(
    date DATE,
    details STRING,
    address STRING
)

-- Add values
INSERT INTO `gcp-tour-276710.thefellowcoder.store`
VALUES
('2021-07-14', '<h1>Nike Shoes</h1><p>Base: $450 Addon: $20</p><p>Support email: help@nike.com</p>','Los Angeles, California 90001 '),
('2021-06-13', '<h1>Rebook Shoes</h1><p>Base: $150 Addon: $10</p><p>Support email: help@rebook.com</p>','Sacramento, California 94203 '),
('2021-07-11', '<h1>Adidas Shoes</h1><p>Base: $350 Addon: $30</p><p>Support email: help@adidas.com</p>','Beverly Hills, California 90209 '),
('2021-07-11', '<h1>Carnival All Rounder Shoes</h1><p>Base: $250 Addon: $0</p>','Beverly Hills, California 90209 ')

```

Sample Queries
--------------

Lets see each of the constructs in action

-   REGEXP_CONTAINS example

```
-- All stores that have a support email
select * from `gcp-tour-276710.thefellowcoder.store` where REGEXP_CONTAINS(details, r'\S+@\S+\.\S+')
```

-   REGEXP_EXTRACT example

```
-- Extract Product Names
select REGEXP_EXTRACT(details, r'<h1>([^<]+)<\/h1>') from `gcp-tour-276710.thefellowcoder.store`
```

-   REGEXP_EXTRACT_ALL example

```
-- Extract all prices
select REGEXP_EXTRACT_ALL(details, r'\$(.\d+)') from `gcp-tour-276710.thefellowcoder.store`
```

-   REGEXP_INSTR example

```
-- Get index of email
select details, REGEXP_INSTR(details, r'\S+@\S+\.\S+') from `gcp-tour-276710.thefellowcoder.store`
```

-   REGEXP_REPLACE example

```
-- Replace all email-ids
select REGEXP_REPLACE(details, r'\S+@\S+\.\S+', 'admin@thefellowcoder.com') from `gcp-tour-276710.thefellowcoder.store`
```

Common Use-cases:
-----------------

### Extract part of the string with regex

This is one of the most common use-cases wherein we must extract substring that matches a regex.

```
-- Extract product names from all details
select REGEXP_EXTRACT(details, r'<h1>([^<]+)<\/h1>') from `gcp-tour-276710.thefellowcoder.store`
```

### Replace regex with string

Let's say you want to sanitize the string and remove all special characters from the string.

```
-- remove special characters
select details,REGEXP_REPLACE(details, r'[^0-9a-zA-Z]+',' ') from `gcp-tour-276710.thefellowcoder.store`
```

### Matches any of the regex patterns

check for multiple regex patterns for a string

```
-- check for pincodes starting with 90/94
select address,REGEXP_EXTRACT(address, r'9[0|4]\d+') as pincode from `gcp-tour-276710.thefellowcoder.store`
```

### Useful regex examples for data cleaning.

| String | Regex | Output |
| --- | --- | --- |
| `<h1>Hello World!</h1>` | `<h1>([^<]+)<\/h1>` | Hello World! |
| <p>Support email: help@rebook.com</p> | \w+@\w+\.\w+ | help@rebook.com |
| Rebook ShOes | (?i)shoes | ShOes |
| This,contains$special\characters | [^0-9a-zA-Z]+ | This contains special characters |
| String needs to be trimmed. | ^(\s+).*?(\s+)$ | String needs to be trimmed.|



Hope you found this post useful,  do check out my [blog](https://thefellowcoder.com/blog/) for more such content.