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String functions (regular expressions)

REGEXP_SUBSTR

Returns the substring that matches a regular expression within a string.

See also: String functions (regular expressions)

Syntax

REGEXP_SUBSTR( <subject> , <pattern> [ , <position> [ , <occurrence> [ , <regex_parameters> [ , <group_num> ] ] ] ] )
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Arguments

Required:

subject

The string to search for matches.

pattern

Pattern to match.

For guidelines on specifying patterns, see String functions (regular expressions).

Optional:

position

Number of characters from the beginning of the string where the function starts searching for matches.

Default: 1 (the search for a match starts at the first character on the left)

occurrence

Specifies the first occurrence of the pattern from which to start returning matches.

The function skips the first occurrence - 1 matches. For example, if there are 5 matches and you specify 3 for the occurrence argument, the function ignores the first two matches and returns the third, fourth, and fifth matches.

Default: 1

regex_parameters

String of one or more characters that specifies the parameters used for searching for matches. Supported values:

Parameter

Description

c

Case-sensitive matching

i

Case-insensitive matching

m

Multi-line mode

e

Extract submatches

s

POSIX wildcard character . matches \n

Default: c

For more details, see Specifying the parameters for the regular expression.

Note

By default, REGEXP_SUBSTR returns the entire matching part of the subject. However, if the e (for “extract”) parameter is specified, REGEXP_SUBSTR returns the part of the subject that matches the first group in the pattern. If e is specified but a group_num is not also specified, then the group_num defaults to 1 (the first group). If there is no sub-expression in the pattern, REGEXP_SUBSTR behaves as if e was not set. For examples that use e, see Examples in this topic.

group_num

Specifies which group to extract. Groups are specified by using parentheses in the regular expression.

If a group_num is specified, Snowflake allows extraction even if the 'e' option was not also specified. The 'e' is implied.

Snowflake supports up to 1024 groups.

For examples that use group_num, see the Examples in this topic.

Returns

The function returns a value of type VARCHAR that is the matching substring.

The function returns NULL in the following cases:

  • No match is found.

  • Any argument is NULL.

Usage notes

For additional information on using regular expressions, see String functions (regular expressions).

Collation details

Arguments with collation specifications currently aren’t supported.

Examples

The documentation of the REGEXP_INSTR function contains many examples that use both REGEXP_SUBSTR and REGEXP_INSTR. You might want to look at those examples, too.

These examples use the strings created below:

CREATE OR REPLACE TABLE demo2 (id INT, string1 VARCHAR);

INSERT INTO demo2 (id, string1) VALUES
    (2, 'It was the best of times, it was the worst of times.'),
    (3, 'In    the   string   the   extra   spaces  are   redundant.'),
    (4, 'A thespian theater is nearby.');

SELECT * FROM demo2;
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+----+-------------------------------------------------------------+
| ID | STRING1                                                     |
|----+-------------------------------------------------------------|
|  2 | It was the best of times, it was the worst of times.        |
|  3 | In    the   string   the   extra   spaces  are   redundant. |
|  4 | A thespian theater is nearby.                               |
+----+-------------------------------------------------------------+

The strings have the following characteristics:

  • The string with an id of 2 has multiple occurrences of the word “the”.

  • The string with an id of 3 has multiple occurrences of the word “the” with extra blank spaces between the words.

  • The string with an id of 4 has the character sequence “the” inside multiple words (“thespian” and “theater”), but without the word “the” by itself.

This example looks for first occurrence of the word the, followed by one or more non-word characters (for example, the whitespace separating words), followed by one or more word characters.

“Word characters” include not only the letters a-z and A-Z, but also the underscore (“_”) and the decimal digits 0-9, but not whitespace, punctuation, and so on.

SELECT id,
       REGEXP_SUBSTR(string1, 'the\\W+\\w+') AS result
  FROM demo2
  ORDER BY id;
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+----+--------------+
| ID | RESULT       |
|----+--------------|
|  2 | the best     |
|  3 | the   string |
|  4 | NULL         |
+----+--------------+

Starting from position 1 of the string, look for the second occurrence of the word the, followed by one or more non-word characters, followed by one or more word characters.

SELECT id,
       REGEXP_SUBSTR(string1, 'the\\W+\\w+', 1, 2) AS result
  FROM demo2
  ORDER BY id;
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+----+-------------+
| ID | RESULT      |
|----+-------------|
|  2 | the worst   |
|  3 | the   extra |
|  4 | NULL        |
+----+-------------+

Starting from position 1 of the string, look for the second occurrence of the word the, followed by one or more non-word characters, followed by one or more word characters.

Rather than returning the entire match, return only the “group” (for example, the portion of the substring that matches the part of the regular expression in parentheses). In this case, the returned value should be the word after “the”.

SELECT id,
       REGEXP_SUBSTR(string1, 'the\\W+(\\w+)', 1, 2, 'e', 1) AS result
  FROM demo2
  ORDER BY id;
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+----+--------+
| ID | RESULT |
|----+--------|
|  2 | worst  |
|  3 | extra  |
|  4 | NULL   |
+----+--------+

This example shows how to retrieve the second word from the first, second, and third matches of a two-word pattern in which the first word is A. This example also shows that trying to go beyond the last pattern causes Snowflake to return NULL.

First, create a table and insert data:

CREATE OR REPLACE TABLE test_regexp_substr (string1 VARCHAR);;
INSERT INTO test_regexp_substr (string1) VALUES ('A MAN A PLAN A CANAL');
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Run the query:

SELECT REGEXP_SUBSTR(string1, 'A\\W+(\\w+)', 1, 1, 'e', 1) AS result1,
       REGEXP_SUBSTR(string1, 'A\\W+(\\w+)', 1, 2, 'e', 1) AS result2,
       REGEXP_SUBSTR(string1, 'A\\W+(\\w+)', 1, 3, 'e', 1) AS result3,
       REGEXP_SUBSTR(string1, 'A\\W+(\\w+)', 1, 4, 'e', 1) AS result4
  FROM test_regexp_substr;
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+---------+---------+---------+---------+
| RESULT1 | RESULT2 | RESULT3 | RESULT4 |
|---------+---------+---------+---------|
| MAN     | PLAN    | CANAL   | NULL    |
+---------+---------+---------+---------+

This example shows how to retrieve the first, second, and third groups within the first occurrence of the pattern. In this case, the returned values are the individual letters of the word MAN.

SELECT REGEXP_SUBSTR(string1, 'A\\W+(\\w)(\\w)(\\w)', 1, 1, 'e', 1) AS result1,
       REGEXP_SUBSTR(string1, 'A\\W+(\\w)(\\w)(\\w)', 1, 1, 'e', 2) AS result2,
       REGEXP_SUBSTR(string1, 'A\\W+(\\w)(\\w)(\\w)', 1, 1, 'e', 3) AS result3
  FROM test_regexp_substr;
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+---------+---------+---------+
| RESULT1 | RESULT2 | RESULT3 |
|---------+---------+---------|
| M       | A       | N       |
+---------+---------+---------+

Here are some additional examples.

Create a table and insert data:

CREATE OR REPLACE TABLE message(body VARCHAR(255));

INSERT INTO message VALUES
  ('Hellooo World'),
  ('How are you doing today?'),
  ('the quick brown fox jumps over the lazy dog'),
  ('PACK MY BOX WITH FIVE DOZEN LIQUOR JUGS');
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Return the first match that contains a lowercase o:

SELECT body,
       REGEXP_SUBSTR(body, '\\b\\S*o\\S*\\b') AS result
  FROM message;
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+---------------------------------------------+---------+
| BODY                                        | RESULT  |
|---------------------------------------------+---------|
| Hellooo World                               | Hellooo |
| How are you doing today?                    | How     |
| the quick brown fox jumps over the lazy dog | brown   |
| PACK MY BOX WITH FIVE DOZEN LIQUOR JUGS     | NULL    |
+---------------------------------------------+---------+

Return the first match that contains a lowercase o, starting at the third character in the subject:

SELECT body,
       REGEXP_SUBSTR(body, '\\b\\S*o\\S*\\b', 3) AS result
  FROM message;
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+---------------------------------------------+--------+
| BODY                                        | RESULT |
|---------------------------------------------+--------|
| Hellooo World                               | llooo  |
| How are you doing today?                    | you    |
| the quick brown fox jumps over the lazy dog | brown  |
| PACK MY BOX WITH FIVE DOZEN LIQUOR JUGS     | NULL   |
+---------------------------------------------+--------+

Return the third match that contains a lowercase o, starting at the third character in the subject:

SELECT body,
       REGEXP_SUBSTR(body, '\\b\\S*o\\S*\\b', 3, 3) AS result
  FROM message;
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+---------------------------------------------+--------+
| BODY                                        | RESULT |
|---------------------------------------------+--------|
| Hellooo World                               | NULL   |
| How are you doing today?                    | today  |
| the quick brown fox jumps over the lazy dog | over   |
| PACK MY BOX WITH FIVE DOZEN LIQUOR JUGS     | NULL   |
+---------------------------------------------+--------+

Return the third match that contains a lowercase o, starting at the third character in the subject, with case-insensitive matching:

SELECT body,
       REGEXP_SUBSTR(body, '\\b\\S*o\\S*\\b', 3, 3, 'i') AS result
  FROM message;
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+---------------------------------------------+--------+
| BODY                                        | RESULT |
|---------------------------------------------+--------|
| Hellooo World                               | NULL   |
| How are you doing today?                    | today  |
| the quick brown fox jumps over the lazy dog | over   |
| PACK MY BOX WITH FIVE DOZEN LIQUOR JUGS     | LIQUOR |
+---------------------------------------------+--------+

This example shows that you can explicitly omit any regular expression parameters by specifying empty string.

SELECT body,
       REGEXP_SUBSTR(body, '(H\\S*o\\S*\\b).*', 1, 1, '') AS result
  FROM message;
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+---------------------------------------------+--------------------------+
| BODY                                        | RESULT                   |
|---------------------------------------------+--------------------------|
| Hellooo World                               | Hellooo World            |
| How are you doing today?                    | How are you doing today? |
| the quick brown fox jumps over the lazy dog | NULL                     |
| PACK MY BOX WITH FIVE DOZEN LIQUOR JUGS     | NULL                     |
+---------------------------------------------+--------------------------+

The following example illustrates overlapping occurrences. First, create a table and insert data:

CREATE OR REPLACE TABLE overlap (
  id NUMBER,
  a STRING);

INSERT INTO overlap VALUES (1, ',abc,def,ghi,jkl,');
INSERT INTO overlap VALUES (2, ',abc,,def,,ghi,,jkl,');

SELECT * FROM overlap;
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+----+----------------------+
| ID | A                    |
|----+----------------------|
|  1 | ,abc,def,ghi,jkl,    |
|  2 | ,abc,,def,,ghi,,jkl, |
+----+----------------------+

Run a query that finds the second occurrence of the following pattern in each row: a punctuation mark followed by digits and letters, followed by a punctuation mark.

SELECT id,
       REGEXP_SUBSTR(a,'[[:punct:]][[:alnum:]]+[[:punct:]]', 1, 2) AS result
  FROM overlap;
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+----+--------+
| ID | RESULT |
|----+--------|
|  1 | ,ghi,  |
|  2 | ,def,  |
+----+--------+

The following example creates a JSON object from an Apache HTTP Server access log using pattern matching and concatenation. First, create a table and insert data:

CREATE OR REPLACE TABLE test_regexp_log (logs VARCHAR);

INSERT INTO test_regexp_log (logs) VALUES
  ('127.0.0.1 - - [10/Jan/2018:16:55:36 -0800] "GET / HTTP/1.0" 200 2216'),
  ('192.168.2.20 - - [14/Feb/2018:10:27:10 -0800] "GET /cgi-bin/try/ HTTP/1.0" 200 3395');

SELECT * from test_regexp_log
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+-------------------------------------------------------------------------------------+
| LOGS                                                                                |
|-------------------------------------------------------------------------------------|
| 127.0.0.1 - - [10/Jan/2018:16:55:36 -0800] "GET / HTTP/1.0" 200 2216                |
| 192.168.2.20 - - [14/Feb/2018:10:27:10 -0800] "GET /cgi-bin/try/ HTTP/1.0" 200 3395 |
+-------------------------------------------------------------------------------------+

Run a query:

SELECT '{ "ip_addr":"'
       || REGEXP_SUBSTR (logs,'\\b\\d{1,3}\.\\d{1,3}\.\\d{1,3}\.\\d{1,3}\\b')
       || '", "date":"'
       || REGEXP_SUBSTR (logs,'([\\w:\/]+\\s[+\-]\\d{4})')
       || '", "request":"'
       || REGEXP_SUBSTR (logs,'\"((\\S+) (\\S+) (\\S+))\"', 1, 1, 'e')
       || '", "status":"'
       || REGEXP_SUBSTR (logs,'(\\d{3}) \\d+', 1, 1, 'e')
       || '", "size":"'
       || REGEXP_SUBSTR (logs,'\\d{3} (\\d+)', 1, 1, 'e')
       || '"}' as Apache_HTTP_Server_Access
  FROM test_regexp_log;
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+-----------------------------------------------------------------------------------------------------------------------------------------+
| APACHE_HTTP_SERVER_ACCESS                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------|
| { "ip_addr":"127.0.0.1", "date":"10/Jan/2018:16:55:36 -0800", "request":"GET / HTTP/1.0", "status":"200", "size":"2216"}                |
| { "ip_addr":"192.168.2.20", "date":"14/Feb/2018:10:27:10 -0800", "request":"GET /cgi-bin/try/ HTTP/1.0", "status":"200", "size":"3395"} |
+-----------------------------------------------------------------------------------------------------------------------------------------+
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