Array Functions

array_append(anyarray, anyelement)

Description: Appends an element to the end of an array and supports only one-dimensional arrays.

Return type: anyarray.

Example:

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postgres=#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 supports only one-dimensional arrays.

Return type: anyarray.

Example:

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

postgres=#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 an array.

Return type: int.

Example:

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

array_dims(anyarray)

Description: Returns a textual representation of the array's dimensions.

Return type: text.

Example:

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postgres=#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 specified array dimension.

Return type: int.

Example:

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

array_lower(anyarray, int)

Description: Returns the lower bound of the specified array dimension.

Return type: int.

Example:

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

array_upper(anyarray, int)

Description: Returns the upper bound of the specified array dimension.

Return type: int.

Example:

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postgres=#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 for the array and the second text to substitute for null values in the array.

Return type: text.

Example:

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

In string_to_array, if the null string parameter is omitted or is NULL, substrings in the string without input content are replaced with NULL.

In array_to_string, if the null string parameter is omitted or is NULL, any null elements in the array are skipped during processing and do not appear in the output string.

string_to_array(text, text [, text])

Description: Uses the second text to specify a delimiter and the third optional text as a template for replacing NULL values. If a split substring exactly matches the third optional text, it is replaced with NULL.

Return type: text[].

Example:

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postgres=#SELECT string_to_array('xx~^~yy~^~zz', '~^~', 'yy') AS RESULT;
    result    
--------------
 {xx,NULL,zz}
(1 row)
postgres=#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 becomes a separate element in the resulting array. If the delimiter is an empty string, the entire input string becomes a single-element array. Otherwise, the input string is split at each occurrence of the delimiter string.

unnest(anyarray)

Description: Expands an array into a set of rows.

Return type: setof anyelement.

Example:

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

The unnest function is used in conjunction with the string_to_array function. To transform an array into columns, first split the string into an array using commas, then expand the array into columns:

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

interval(N, N1, N2, N3 ... )

Description: Searches the input integer array and returns the last array index that is less than or equal to the target parameter n. If n is NULL, -1 is returned. The interval function does not support the interval(N, N1) scenario. This function is only supported by clusters of version 8.2.0 or later.

Return type: int.

Example:

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postgres=#SELECT INTERVAL(10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 11) AS RESULT;
 result    
--------
     11
(1 row)

split(string, delim)

Description: Splits the string according to the delimiter and returns an array. This function is only supported by clusters of version 8.2.0 or later.

Return type: text[].

Example:

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postgres=#SELECT SPLIT('a-b-c-d-e', '-') AS RESULT;
   result    
-------------
 {a,b,c,d,e}
(1 row)
postgres=#SELECT SPLIT('a-b-c-d-e', '-')[4] AS RESULT;
 result   
--------
 d
(1 row)