Array Functions

array_append(anyarray, anyelement)

Description: Appends an element to the end of an array, and only supports dimension-1 arrays.

Return type: anyarray

Example:

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SELECT array_append(ARRAY[1,2], 3) AS RESULT;
 result  
---------
 {1,2,3}
(1 row)

array_prepend(anyelement, anyarray)

Description: Appends an element to the beginning of an array, and only supports dimension-1 arrays.

Return type: anyarray

Example:

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SELECT array_prepend(1, ARRAY[2,3]) AS RESULT;
 result  
---------
 {1,2,3}
(1 row)

array_cat(anyarray, anyarray)

Description: Concatenates two arrays, and supports multi-dimensional arrays.

Return type: anyarray

Example:

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SELECT array_cat(ARRAY[1,2,3], ARRAY[4,5]) AS RESULT;
   result    
-------------
 {1,2,3,4,5}
(1 row)

SELECT array_cat(ARRAY[[1,2],[4,5]], ARRAY[6,7]) AS RESULT;
       result        
---------------------
 {{1,2},{4,5},{6,7}}
(1 row)

array_ndims(anyarray)

Description: Returns the number of dimensions of the array.

Return type: int

Example:

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SELECT array_ndims(ARRAY[[1,2,3], [4,5,6]]) AS RESULT;
 result 
--------
      2
(1 row)

array_dims(anyarray)

Description: Returns a text representation of array's dimensions.

Return type: text

Example:

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SELECT array_dims(ARRAY[[1,2,3], [4,5,6]]) AS RESULT;
   result   
------------
 [1:2][1:3]
(1 row)

array_length(anyarray, int)

Description: Returns the length of the requested array dimension.

Return type: int

Example:

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SELECT array_length(array[1,2,3], 1) AS RESULT;
 result 
--------
      3
(1 row)

array_lower(anyarray, int)

Description: Returns lower bound of the requested array dimension.

Return type: int

Example:

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SELECT array_lower('[0:2]={1,2,3}'::int[], 1) AS RESULT;
 result 
--------
      0
(1 row)

array_upper(anyarray, int)

Description: Returns upper bound of the requested array dimension.

Return type: int

Example:

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SELECT array_upper(ARRAY[1,8,3,7], 1) AS RESULT;
 result 
--------
      4
(1 row)

array_to_string(anyarray, text [, text])

Description: Uses the first text as the new delimiter and the second text to replace NULL values.

Return type: text

Example:

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SELECT array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*') AS RESULT;
  result   
-----------
 1,2,3,*,5
(1 row)

In array_to_string, if the null-string parameter is omitted or NULL, any null elements in the array are simply skipped and not represented in the output string.

string_to_array(text, text [, text])

Description: Uses the second text as the new delimiter and the third text as the substring to be replaced by NULL values. A substring can be replaced by NULL values only when it is the same as the third text.

Return type: text[]

Example:

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SELECT string_to_array('xx~^~yy~^~zz', '~^~', 'yy') AS RESULT;
    result    
--------------
 {xx,NULL,zz}
(1 row)
SELECT string_to_array('xx~^~yy~^~zz', '~^~', 'y') AS RESULT;
   result   
------------
 {xx,yy,zz}
(1 row)

• In string_to_array, if the delimiter parameter is NULL, each character in the input string will become a separate element in the resulting array. If the delimiter is an empty string, then the entire input string is returned as a one-element array. Otherwise the input string is split at each occurrence of the delimiter string.
• In string_to_array, if the null-string parameter is omitted or NULL, none of the substrings of the input will be replaced by NULL.

unnest(anyarray)

Description: Expands an array to a set of rows.

Return type: setof anyelement

Example:

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SELECT unnest(ARRAY[1,2]) AS RESULT;
 result 
--------
      1
      2
(2 rows)

The unnest function is used together with the string_to_array array. To convert an array to columns, the statement first splits a string into arrays by comma, and then converts the arrays into columns.

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SELECT unnest(string_to_array('a,b,c,d',',')) AS RESULT;
 result
--------
 a
 b
 c
 d
(4 rows)