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Pattern-Matching Functions

Pattern-matching functions allow you to find regular expression patterns in strings or attributes. Regular expressions can formally represent various string search patterns using different special characters to indicate wildcards, positional characters, repetition, optional or mandatory sequences of letters, etc. N1QL functions are available to find matching patterns, find position of matching pattern, or replace a pattern with a new string.

For more information on all supported REGEX patterns, see https://golang.org/pkg/regexp/syntax.

Couchbase Server 4.x N1QL supports regular expressions supported by The Go Programming Language version 1.4.2. From Couchbase Server 5.0, The Go Programming Language version 1.8 is supported.

REGEXP_CONTAINS(expression, pattern)

Arguments

expression

String, or any N1QL expression that evaluates to a string.

pattern

String representing a supported regular expression.

Return Value

Returns TRUE if the string value contains any sequence that matches the regular expression pattern.

Example

Example 1.
SELECT name
FROM `travel-sample`
WHERE type = "landmark" AND REGEX_CONTAINS(name, "In+.*")
LIMIT 5;
Results
[
  {
    "name": "Beijing Inn"
  },
  {
    "name": "Sportsman Inn"
  },
  {
    "name": "In-N-Out Burger"
  },
  {
    "name": "Mel's Drive-In"
  },
  {
    "name": "Inverness Castle"
  }
]

REGEXP_LIKE(expression, pattern)

Arguments

expression

String, or any N1QL expression that evaluates to a string.

pattern

String representing a supported regular expression.

Return Value

Returns TRUE if the string value exactly matches the regular expression pattern.

Example

Example 2.
SELECT name
FROM `travel-sample`
WHERE type = "landmark" and REGEX_LIKE(name, "In+.*")
LIMIT 5;
Results
[
  {
    "name": "In-N-Out Burger"
  },
  {
    "name": "Inverness Castle"
  },
  {
    "name": "Inverness Museum & Art Gallery"
  },
  {
    "name": "Inverness Botanic Gardens"
  },
  {
    "name": "International Petroleum Exchange"
  }
]

REGEXP_MATCHES(expression, pattern)

Arguments

expression

String, or any N1QL expression that evaluates to a string.

pattern

String representing a supported regular expression.

Return Value

Returns an array of all substrings matching the expression pattern within the input string expression. Returns an empty array if no match is found.

Examples

Example 3.

The following query finds all words beginning with upper or lower case B.

SELECT REGEXP_MATCHES("So, 'twas better Betty Botter bought a bit of better butter", "\\b[Bb]\\w+"); (1)
Results
[
  {
    "$1": [
      "better",
      "Betty",
      "Botter",
      "bought",
      "bit",
      "better",
      "butter"
    ]
  }
]
1 The backslash that introduces an escape sequence in the regular expression must itself be escaped by another backslash in the N1QL query. So \b (word boundary) must be entered as \\b and \w (word character) must be entered as \\w.
Example 4.

The following query finds sequences of two words beginning with upper or lower case B.

SELECT REGEXP_MATCHES("So, 'twas better Betty Botter bought a bit of better butter", "\\b[Bb]\\w+ \\b[Bb]\\w+");
Results
[
  {
    "$1": [
      "better Betty",
      "Botter bought", (1)
      "better butter"
    ]
  }
]
1 Note that Betty Botter is not found in this example, because Betty has already been found by the first match.

REGEXP_POSITION(expression, pattern)

Arguments

expression

String, or any N1QL expression that evaluates to a string.

pattern

String representing a supported regular expression.

Return Value

Returns first position of the occurrence of the regular expression pattern within the input string expression. Returns -1 if no match is found. Position counting starts from zero.

Example

Example 5.

The following query finds positions of first occurrence of vowels in each word of the name attribute.

SELECT name, ARRAY REGEXP_POSITION(x, "[aeiou]") FOR x IN TOKENS(name) END
FROM `travel-sample`
WHERE type = "hotel"
LIMIT 2;
Results
[
  {
    "$1": [
      1,
      1,
      1
    ],
    "name": "Medway Youth Hostel"
  },
  {
    "$1": [
      1,
      2,
      1
    ],
    "name": "The Balmoral Guesthouse"
  }
]

REGEXP_REPLACE(expression, pattern, repl [, n])

Arguments

expression

String, or any N1QL expression that evaluates to a string.

pattern

String representing a supported regular expression.

repl

String, or any N1QL expression that evaluates to a string.

n

[Optional] The maximum number of times to find and replace the matching pattern.

Return Value

Returns new string with occurrences of pattern replaced with repl. If n is given, at the most n replacements are performed. If n is not provided, all matching occurrences are replaced.

Examples

Example 6.
SELECT REGEXP_REPLACE("N1QL is Sql (in fact, sql++) for NoSql", "[sS][qQ][lL]", "SQL"),
       REGEXP_REPLACE("Winning innings Inn", "[Ii]n+", "Hotel", 6),
       REGEXP_REPLACE("Winning innings Inn", "[IiNn]+g", upper("inning"), 2);
Results
[
  {
    "$1": "N1QL is SQL (in fact, SQL++) for NoSQL",
    "$2": "WHotelHotelg HotelHotelgs Hotel",
    "$3": "WINNING INNINGs Inn"
  }
]
Example 7.

In this example, the query retrieves first 4 documents and replaces the pattern of repeating n with emphasized ‘NNNN’.

SELECT name, REGEXP_REPLACE(name, "n+", "NNNN") as new_name
FROM `travel-sample`
LIMIT 4;
Results
[
  {
    "name": "40-Mile Air",
    "new_name": "40-Mile Air"
  },
  {
    "name": "Texas Wings",
    "new_name": "Texas WiNNNNgs"
  },
  {
    "name": "Atifly",
    "new_name": "Atifly"
  },
  {
    "name": "Jc royal.britannica",
    "new_name": "Jc royal.britaNNNNica"
  }
]

REGEXP_SPLIT(expression, pattern)

Arguments

expression

String, or any N1QL expression that evaluates to a string.

pattern

String representing a supported regular expression.

Return Value

Returns an array of all the substrings created by splitting the input string expression at each occurrence of the expression pattern. Returns an empty array if no match is found.

Example

Example 8.
SELECT REGEXP_SPLIT("C:\\Program Files\\couchbase\\server\\bin", "[\\\\]") AS Windows, (1)
REGEXP_SPLIT("/opt/couchbase/bin", "/") AS Unix;
Results
[
  {
    "Unix": [
      "", (2)
      "opt",
      "couchbase",
      "bin"
    ],
    "Windows": [
      "C:",
      "Program Files",
      "couchbase",
      "server",
      "bin"
    ]
  }
]
1 The regular expression [\\\\] matches the escaped backslash \\.
2 The REGEXP_SPLIT function returns any zero-length matches that occur at the start of the expression string, or immediately after a previous match.