Impala String Functions

String functions are classified as those primarily accepting or returning STRING, VARCHAR, or CHAR data types, for example to measure the length of a string or concatenate two strings together.

All the functions that accept STRING arguments also accept the VARCHAR and CHAR types introduced in Impala 2.0.
Whenever VARCHAR or CHAR values are passed to a function that returns a string value, the return type is normalized to STRING. For example, a call to concat() with a mix of STRING, VARCHAR, and CHAR arguments produces a STRING result.

Related information:

The string functions operate mainly on these data types: STRING Data Type, VARCHAR Data Type (CDH 5.2 or higher only), and CHAR Data Type (CDH 5.2 or higher only).

Function reference:

Impala supports the following string functions:

ascii(string str)

Purpose: Returns the numeric ASCII code of the first character of the argument.

Return type: int

btrim(string a), btrim(string a, string chars_to_trim)

Purpose: Removes all instances of one or more characters from the start and end of a STRING value. By default, removes only spaces. If a non-NULL optional second argument is specified, the function removes all occurrences of characters in that second argument from the beginning and end of the string.

Return type: string

Added in: CDH 5.5.0 (Impala 2.3.0)

Examples:

The following examples show the default btrim() behavior, and what changes when you specify the optional second argument. All the examples bracket the output value with [ ] so that you can see any leading or trailing spaces in the btrim() result. By default, the function removes and number of both leading and trailing spaces. When the second argument is specified, any number of occurrences of any character in the second argument are removed from the start and end of the input string; in this case, spaces are not removed (unless they are part of the second argument) and any instances of the characters are not removed if they do not come right at the beginning or end of the string.

-- Remove multiple spaces before and one space after.
select concat('[',btrim('    hello '),']');
+---------------------------------------+
| concat('[', btrim('    hello '), ']') |
+---------------------------------------+
| [hello]                               |
+---------------------------------------+

-- Remove any instances of x or y or z at beginning or end. Leave spaces alone.
select concat('[',btrim('xy    hello zyzzxx','xyz'),']');
+------------------------------------------------------+
| concat('[', btrim('xy    hello zyzzxx', 'xyz'), ']') |
+------------------------------------------------------+
| [    hello ]                                         |
+------------------------------------------------------+

-- Remove any instances of x or y or z at beginning or end.
-- Leave x, y, z alone in the middle of the string.
select concat('[',btrim('xyhelxyzlozyzzxx','xyz'),']');
+----------------------------------------------------+
| concat('[', btrim('xyhelxyzlozyzzxx', 'xyz'), ']') |
+----------------------------------------------------+
| [helxyzlo]                                         |
+----------------------------------------------------+

char_length(string a), character_length(string a)

Purpose: Returns the length in characters of the argument string. Aliases for the length() function.

Return type: int

chr(int character_code)

Purpose: Returns a character specified by a decimal code point value. The interpretation and display of the resulting character depends on your system locale. Because consistent processing of Impala string values is only guaranteed for values within the ASCII range, only use this function for values corresponding to ASCII characters. In particular, parameter values greater than 255 return an empty string.

Return type: string

Usage notes: Can be used as the inverse of the ascii() function, which converts a character to its numeric ASCII code.

Added in: CDH 5.5.0 (Impala 2.3.0)

Examples:

SELECT chr(65);
+---------+
| chr(65) |
+---------+
| A       |
+---------+

SELECT chr(97);
+---------+
| chr(97) |
+---------+
| a       |
+---------+

concat(string a, string b...)

Purpose: Returns a single string representing all the argument values joined together.

Return type: string

Usage notes: concat() and concat_ws() are appropriate for concatenating the values of multiple columns within the same row, while group_concat() joins together values from different rows.

concat_ws(string sep, string a, string b...)

Purpose: Returns a single string representing the second and following argument values joined together, delimited by a specified separator.

Return type: string

Usage notes: concat() and concat_ws() are appropriate for concatenating the values of multiple columns within the same row, while group_concat() joins together values from different rows.

find_in_set(string str, string strList)

Purpose: Returns the position (starting from 1) of the first occurrence of a specified string within a comma-separated string. Returns NULL if either argument is NULL, 0 if the search string is not found, or 0 if the search string contains a comma.

Return type: int

group_concat(string s [, string sep])

Purpose: Returns a single string representing the argument value concatenated together for each row of the result set. If the optional separator string is specified, the separator is added between each pair of concatenated values.

Return type: string

Usage notes: concat() and concat_ws() are appropriate for concatenating the values of multiple columns within the same row, while group_concat() joins together values from different rows.

By default, returns a single string covering the whole result set. To include other columns or values in the result set, or to produce multiple concatenated strings for subsets of rows, include a GROUP BY clause in the query.

Strictly speaking, group_concat() is an aggregate function, not a scalar function like the others in this list. For additional details and examples, see GROUP_CONCAT Function.

initcap(string str)

Purpose: Returns the input string with the first letter capitalized.

Return type: string

instr(string str, string substr)

Purpose: Returns the position (starting from 1) of the first occurrence of a substring within a longer string.

Return type: int

length(string a)

Purpose: Returns the length in characters of the argument string.

Return type: int

locate(string substr, string str[, int pos])

Purpose: Returns the position (starting from 1) of the first occurrence of a substring within a longer string, optionally after a particular position.

Return type: int

lower(string a), lcase(string a)

Purpose: Returns the argument string converted to all-lowercase.

Return type: string

Usage notes:

In CDH 5.7 / Impala 2.5 and higher, you can simplify queries that use many UPPER() and LOWER() calls to do case-insensitive comparisons, by using the ILIKE or IREGEXP operators instead. See ILIKE Operator and IREGEXP Operator for details.

lpad(string str, int len, string pad)

Purpose: Returns a string of a specified length, based on the first argument string. If the specified string is too short, it is padded on the left with a repeating sequence of the characters from the pad string. If the specified string is too long, it is truncated on the right.

Return type: string

ltrim(string a)

Purpose: Returns the argument string with any leading spaces removed from the left side.

Return type: string

parse_url(string urlString, string partToExtract [, string keyToExtract])

Purpose: Returns the portion of a URL corresponding to a specified part. The part argument can be 'PROTOCOL', 'HOST', 'PATH', 'REF', 'AUTHORITY', 'FILE', 'USERINFO', or 'QUERY'. Uppercase is required for these literal values. When requesting the QUERY portion of the URL, you can optionally specify a key to retrieve just the associated value from the key-value pairs in the query string.

Return type: string

Usage notes: This function is important for the traditional Hadoop use case of interpreting web logs. For example, if the web traffic data features raw URLs not divided into separate table columns, you can count visitors to a particular page by extracting the 'PATH' or 'FILE' field, or analyze search terms by extracting the corresponding key from the 'QUERY' field.

regexp_extract(string subject, string pattern, int index)

Purpose: Returns the specified () group from a string based on a regular expression pattern. Group 0 refers to the entire extracted string, while group 1, 2, and so on refers to the first, second, and so on (...) portion.

Return type: string

In Impala 2.0 and later, the Impala regular expression syntax conforms to the POSIX Extended Regular Expression syntax used by the Google RE2 library. For details, see the RE2 documentation. It has most idioms familiar from regular expressions in Perl, Python, and so on, including .*? for non-greedy matches.

In Impala 2.0 and later, a change in the underlying regular expression library could cause changes in the way regular expressions are interpreted by this function. Test any queries that use regular expressions and adjust the expression patterns if necessary. See Incompatible Changes Introduced in Impala 2.0.0 / CDH 5.2.0 for details.

Because the impala-shell interpreter uses the \ character for escaping, use \\ to represent the regular expression escape character in any regular expressions that you submit through impala-shell . You might prefer to use the equivalent character class names, such as [[:digit:]] instead of \d which you would have to escape as \\d.

Examples:

This example shows how group 0 matches the full pattern string, including the portion outside any () group:

[localhost:21000] > select regexp_extract('abcdef123ghi456jkl','.*?(\\d+)',0);
+------------------------------------------------------+
| regexp_extract('abcdef123ghi456jkl', '.*?(\\d+)', 0) |
+------------------------------------------------------+
| abcdef123ghi456                                      |
+------------------------------------------------------+
Returned 1 row(s) in 0.11s

This example shows how group 1 matches just the contents inside the first () group in the pattern string:

[localhost:21000] > select regexp_extract('abcdef123ghi456jkl','.*?(\\d+)',1);
+------------------------------------------------------+
| regexp_extract('abcdef123ghi456jkl', '.*?(\\d+)', 1) |
+------------------------------------------------------+
| 456                                                  |
+------------------------------------------------------+
Returned 1 row(s) in 0.11s

Unlike in earlier Impala releases, the regular expression library used in Impala 2.0 and later supports the .*? idiom for non-greedy matches. This example shows how a pattern string starting with .*? matches the shortest possible portion of the source string, returning the rightmost set of lowercase letters. A pattern string both starting and ending with .*? finds two potential matches of equal length, and returns the first one found (the leftmost set of lowercase letters).

[localhost:21000] > select regexp_extract('AbcdBCdefGHI','.*?([[:lower:]]+)',1);
+--------------------------------------------------------+
| regexp_extract('abcdbcdefghi', '.*?([[:lower:]]+)', 1) |
+--------------------------------------------------------+
| def                                                    |
+--------------------------------------------------------+
[localhost:21000] > select regexp_extract('AbcdBCdefGHI','.*?([[:lower:]]+).*?',1);
+-----------------------------------------------------------+
| regexp_extract('abcdbcdefghi', '.*?([[:lower:]]+).*?', 1) |
+-----------------------------------------------------------+
| bcd                                                       |
+-----------------------------------------------------------+

regexp_like(string source, string pattern[, string options])

Purpose: Returns true or false to indicate whether the source string contains anywhere inside it the regular expression given by the pattern. The optional third argument consists of letter flags that change how the match is performed, such as i for case-insensitive matching.

Syntax:

The flags that you can include in the optional third argument are:

c: Case-sensitive matching (the default).
i: Case-insensitive matching. If multiple instances of c and i are included in the third argument, the last such option takes precedence.
m: Multi-line matching. The ^ and $ operators match the start or end of any line within the source string, not the start and end of the entire string.
n: Newline matching. The . operator can match the newline character. A repetition operator such as .* can match a portion of the source string that spans multiple lines.

Return type: boolean

Examples:

This example shows how regexp_like() can test for the existence of various kinds of regular expression patterns within a source string:

-- Matches because the 'f' appears somewhere in 'foo'.
select regexp_like('foo','f');
+-------------------------+
| regexp_like('foo', 'f') |
+-------------------------+
| true                    |
+-------------------------+

-- Does not match because the comparison is case-sensitive by default.
select regexp_like('foo','F');
+-------------------------+
| regexp_like('foo', 'f') |
+-------------------------+
| false                   |
+-------------------------+

-- The 3rd argument can change the matching logic, such as 'i' meaning case-insensitive.
select regexp_like('foo','F','i');
+------------------------------+
| regexp_like('foo', 'f', 'i') |
+------------------------------+
| true                         |
+------------------------------+

-- The familiar regular expression notations work, such as ^ and $ anchors...
select regexp_like('foo','f$');
+--------------------------+
| regexp_like('foo', 'f$') |
+--------------------------+
| false                    |
+--------------------------+

select regexp_like('foo','o$');
+--------------------------+
| regexp_like('foo', 'o$') |
+--------------------------+
| true                     |
+--------------------------+

-- ...and repetition operators such as * and +
select regexp_like('foooooobar','fo+b');
+-----------------------------------+
| regexp_like('foooooobar', 'fo+b') |
+-----------------------------------+
| true                              |
+-----------------------------------+

select regexp_like('foooooobar','fx*y*o*b');
+---------------------------------------+
| regexp_like('foooooobar', 'fx*y*o*b') |
+---------------------------------------+
| true                                  |
+---------------------------------------+

regexp_replace(string initial, string pattern, string replacement)

Purpose: Returns the initial argument with the regular expression pattern replaced by the final argument string.

Return type: string

Examples:

These examples show how you can replace parts of a string matching a pattern with replacement text, which can include backreferences to any () groups in the pattern string. The backreference numbers start at 1, and any \ characters must be escaped as \\.

Replace a character pattern with new text:

[localhost:21000] > select regexp_replace('aaabbbaaa','b+','xyz');
+------------------------------------------+
| regexp_replace('aaabbbaaa', 'b+', 'xyz') |
+------------------------------------------+
| aaaxyzaaa                                |
+------------------------------------------+
Returned 1 row(s) in 0.11s

Replace a character pattern with substitution text that includes the original matching text:

[localhost:21000] > select regexp_replace('aaabbbaaa','(b+)','<\\1>');
+----------------------------------------------+
| regexp_replace('aaabbbaaa', '(b+)', '<\\1>') |
+----------------------------------------------+
| aaa<bbb>aaa                                  |
+----------------------------------------------+
Returned 1 row(s) in 0.11s

Remove all characters that are not digits:

[localhost:21000] > select regexp_replace('123-456-789','[^[:digit:]]','');
+---------------------------------------------------+
| regexp_replace('123-456-789', '[^[:digit:]]', '') |
+---------------------------------------------------+
| 123456789                                         |
+---------------------------------------------------+
Returned 1 row(s) in 0.12s

repeat(string str, int n)

Purpose: Returns the argument string repeated a specified number of times.

Return type: string

reverse(string a)

Purpose: Returns the argument string with characters in reversed order.

Return type: string

rpad(string str, int len, string pad)

Purpose: Returns a string of a specified length, based on the first argument string. If the specified string is too short, it is padded on the right with a repeating sequence of the characters from the pad string. If the specified string is too long, it is truncated on the right.

Return type: string

rtrim(string a)

Purpose: Returns the argument string with any trailing spaces removed from the right side.

Return type: string

space(int n)

Purpose: Returns a concatenated string of the specified number of spaces. Shorthand for repeat(' ',n).

Return type: string

split_part(string source, string delimiter, bigint n)

Purpose: Returns the nth field within a delimited string. The fields are numbered starting from 1. The delimiter can consist of multiple characters, not just a single character. All matching of the delimiter is done exactly, not using any regular expression patterns.

Return type: string

Examples:

These examples show how to retrieve the nth field from a delimited string:

select split_part('x,y,z',',',1);
+-----------------------------+
| split_part('x,y,z', ',', 1) |
+-----------------------------+
| x                           |
+-----------------------------+

select split_part('x,y,z',',',2);
+-----------------------------+
| split_part('x,y,z', ',', 2) |
+-----------------------------+
| y                           |
+-----------------------------+

select split_part('x,y,z',',',3);
+-----------------------------+
| split_part('x,y,z', ',', 3) |
+-----------------------------+
| z                           |
+-----------------------------+

These examples show what happens for out-of-range field positions. Specifying a value less than 1 produces an error. Specifying a value greater than the number of fields returns a zero-length string (which is not the same as NULL).

select split_part('x,y,z',',',0);
ERROR: Invalid field position: 0

with t1 as (select split_part('x,y,z',',',4) nonexistent_field)
  select
      nonexistent_field
    , concat('[',nonexistent_field,']')
    , length(nonexistent_field);
from t1
+-------------------+-------------------------------------+---------------------------+
| nonexistent_field | concat('[', nonexistent_field, ']') | length(nonexistent_field) |
+-------------------+-------------------------------------+---------------------------+
|                   | []                                  | 0                         |
+-------------------+-------------------------------------+---------------------------+

These examples show how the delimiter can be a multi-character value:

select split_part('one***two***three','***',2);
+-------------------------------------------+
| split_part('one***two***three', '***', 2) |
+-------------------------------------------+
| two                                       |
+-------------------------------------------+

select split_part('one\|/two\|/three','\|/',3);
+-------------------------------------------+
| split_part('one\|/two\|/three', '\|/', 3) |
+-------------------------------------------+
| three                                     |
+-------------------------------------------+

strleft(string a, int num_chars)

Purpose: Returns the leftmost characters of the string. Shorthand for a call to substr() with 2 arguments.

Return type: string

strright(string a, int num_chars)

Purpose: Returns the rightmost characters of the string. Shorthand for a call to substr() with 2 arguments.

Return type: string

substr(string a, int start [, int len]), substring(string a, int start [, int len])

Purpose: Returns the portion of the string starting at a specified point, optionally with a specified maximum length. The characters in the string are indexed starting at 1.

Return type: string

translate(string input, string from, string to)

Purpose: Returns the input string with a set of characters replaced by another set of characters.

Return type: string

trim(string a)

Purpose: Returns the input string with both leading and trailing spaces removed. The same as passing the string through both ltrim() and rtrim().

Usage notes: Often used during data cleansing operations during the ETL cycle, if input values might still have surrounding spaces. For a more general-purpose function that can remove other leading and trailing characters besides spaces, see btrim().

Return type: string

upper(string a), ucase(string a)

Purpose: Returns the argument string converted to all-uppercase.

Return type: string

Usage notes:

Conditional Functions

Miscellaneous Functions