Array Functions and Operators

The Ocient® System enables you to work with data as arrays. The system contains functions that work with arrays and operators that enable you to parse data within arrays.

ARRAY_CAT_DISTINCT

Concatenates two or more arrays in the order of the input arguments. After concatenation, the function removes duplicates from the result array while preserving the first occurrence order. The function skips any NULL input arguments. If all input arrays are NULL, the function returns a NULL. If at least one NULL element is present in the array, the function returns a NULL in the result array with the position of the first NULL the function finds in the order of the input arguments.

Syntax

ARRAY_CAT_DISTINCT(input_array1, input_array2 [, ...])

Examples

Concatenate Two Arrays and Remove Duplicates

Concatenate two arrays and remove duplicate elements within the arrays.

SELECT ARRAY_CAT_DISTINCT(ARRAY[1,2,2,3,1], ARRAY[2,3,4,4,5]);

Output: [1,2,3,4,5]

Concatenate Two Arrays with NULLs and Remove Duplicates

Deduplicate the contents of the array. In this case, the array contains NULLs.

SELECT ARRAY_CAT_DISTINCT(ARRAY[1,2,2,NULL,1], ARRAY[2,4,4,NULL]);

Output: [1,2,NULL,4]

ARRAY_DISTINCT

Removes duplicates from an array while preserving the first occurrence order. If at least one NULL is present in the array, the function returns a NULL with the position of the first NULL of the input array in the output array.

Syntax

ARRAY_DISTINCT(input_array)

Examples

Remove Duplicates from an Array

Deduplicate the contents of the array.

SELECT ARRAY_DISTINCT(ARRAY[1,2,2,3,1]);

Output: [1,2,3]

Remove Duplicates from an Array with NULLs

Deduplicate the contents of the array. In this case, the array contains NULLs.

SELECT ARRAY_DISTINCT(ARRAY[1,2,NULL,2,3,NULL,1]);

Output: [1,2,NULL,3]

ARRAY_LENGTH

Returns the length of the array for the specified dimension. If the array is a nested array, the function returns the length of the outermost array.

Syntax

ARRAY_LENGTH(input_array)

Example

Return the length of the array.

SELECT ARRAY_LENGTH(ARRAY[1,2]);

Output: 2

ARRAY_SORT

Sorts and returns the input array based on the natural ordering of its elements. The behavior of this function varies depending on the syntax you use.

Syntaxes

Basic Array Sort

Sorts and returns the input array based on the natural ordering of its elements. If one of the array elements is NULL, then this function sorts the NULL values to the end of the array.

ARRAY_SORT(input_array)

Sort an Array With a Lambda Function

Sorts and returns the input array based on the results of the specified Lambda function. The function should have two arguments representing two elements of the array. This function should return a negative integer, 0, or a positive integer if the first element is less than, equal to, or greater than the second element, respectively.

ARRAY_SORT(input_array,function)

Sort an Array in the Specified Order

Determines how the array handles the order of elements in the array.

ARRAY_SORT(input_array,sort_order)

Sort an Array in the Specified Order with NULL Elements

Determines how the array handles the order of elements in the array and where NULL elements appear.

ARRAY_SORT(input_array,sort_order,nulls_first)

Examples

Sort an Array

Sort an array of three elements [2,3,1].

SELECT ARRAY_SORT(ARRAY[2,3,1]);

Output: [1,2,3]

Sort an Array by Specifying the Sort Order

Sort an array of four elements [2,3,1,NULL] and specify the order of the elements in descending order.

SELECT ARRAY_SORT(ARRAY[2,3,1,NULL],false);

Output: [NULL,3,2,1]

Sort an Array by Specifying the Sort Order and NULL Placement

Sort an array of four elements [2,NULL,3,1] and specify the order of the elements in ascending order, and have the NULL element appear last.

SELECT ARRAY_SORT(ARRAY[2,NULL,3,1],true,false);

Output: [1,2,3,NULL]

UNNEST

Expands each element in an input array into an individual row.

For example, the UNNEST function on an array column of type ARRAY(INT) with values [2, 6] yields two result rows with integers 2 and 6.

The values of the other columns in each input row are unchanged in each corresponding output row. You can specify multiple array columns to unnest the specified arrays from each row in parallel.

Syntax

UNNEST( array_column [, ... ]​ )
   [ WITH <unnest_options> ]
<unnest_options> ::=
   { ORDINALITY [ ord_identifier ]
   | VALUE [ val_identifier ]
   | NULL_INPUT }

The UNNEST function supports these options. When you use only one of these options, enclosing the option in parentheses is optional. However, if you use more than one of these options, you must enclose them in parentheses.

These examples demonstrate how the UNNEST function operates on arrays and other objects. Most of the examples use the data rows from this table.

a   b        c        d     e      f
--------------------------------------------
1   [1, 2]   [6, 9]   []    NULL   [[1, 2], [5], []]
2   [7, 5]   [4]      [3]   [8]    [[6], [9, 4, 7], [3, 8]]

Examples

Expand a Column

This example performs a simple UNNEST on column b.

SELECT UNNEST(b);

Output

b_val
-----------
1
2
7
5

Expand a Column Using theORDINALITYOption

In this example, the ORDINALITY option adds a second return column that represents the index position of the value in the input array.

SELECT UNNEST(b) WITH ORDINALITY;

Output

b_val   b_ord
--------------------
1       1
2       2
7       1
5       2

Expand a Column with Empty Data

In this example, the UNNEST query returns only one row because one of the two rows in column d is an empty array.

If you use the NULL_INPUT option, the query returns a second row with the NULL value.

SELECT UNNEST(d);

Output

d_val
------------
3

Expand a Column with NULL Data

UNNEST also does not return array values that are NULL unless you specify the NULL_INPUT option.

SELECT UNNEST(e);

Output

e_val
------------
8

Expand a Column with Multiple Array Layers

The UNNEST function expands only one array layer.

SELECT UNNEST(f);

Output

f_val
------------
[1,2]
[5]
[]
[6]
[9,4,7]
[3,8]

Expand Columns Using MultipleUNNESTStatements

Multiple UNNEST statements in a query produce a per-row Cartesian product of all the unnested values.

SELECT UNNEST(b), UNNEST(c);

Output

b_val   c_val
------------
1       6
1       9
2       6
2       9
7       4
5       4

Expand Columns Using MultipleUNNESTStatements in Reverse Order

This example uses UNNEST on the same columns but in reverse order.

SELECT UNNEST(c), UNNEST(b);

Output

c_val   b_val
------------
6       1
6       2
9       1
9       2
4       7
4       5

Expand Multiple Columns

In this example, the query unnests two array columns in parallel. Even though it does not include the NULL_INPUT option, the query still returns NULL for column c to correspond with column b.

SELECT UNNEST(b, c);

Output

b_val   c_val
------------
1       6
2       9
7       4
5       NULL

Expand M****ultiple Array Columns

This query unnests two array columns.

SELECT UNNEST(b, d);

Output

b_val   d_val
------------
1       NULL
2       NULL
7       3
5       NULL

Expand Values of Arrays Within Arrays

This example has two layers of UNNEST to capture values of arrays within arrays.

SELECT UNNEST(f_val) FROM (UNNEST(f));

Output

f_val
------------
1
2
5
6
9
4
7
3
8

Expand an Empty Array

This example unnests an empty integer array.

SELECT UNNEST(INT[]());

Output

col_val
------------

The query returns a column of type INT but no rows.

Expand an Empty Array Column Without theNULL_INPUTOption

This example selects the non-array column a and an empty array column. The query returns no rows because empty or NULL array values are not returned unless you specify the NULL_INPUT option.

SELECT a, UNNEST(INT[]());

Output

a   col_val
------------

Expand a Column Without theNULL_INPUTOption

This query does not include the NULL_INPUT option, which causes the result to omit the NULL array values in column e.

SELECT a, UNNEST(e);

Output

a   e_val
------------
1   8
2   8

Expand a Column****with theNULL_INPUTOption

This query includes the NULL_INPUT option, which means that the query returns the NULL values in column e.

SELECT a, UNNEST(e) WITH NULL_INPUT;

Output

a   e_val
------------
1   8
1   NULL
2   8
2   NULL

Expand Arrays with NULL Rows

This example attempts to unnest two arrays, one of which is cast as NULL, while the other is empty.

In both cases, the query returns a column of type INTEGER with no rows because there are no values to unnest.

SELECT UNNEST(CAST(NULL AS INT[]);
SELECT UNNEST(INT[]());

Output

col_val
------------

Other Array Functions

Function Examples

Array Operators

Ocient array operators allow you to concatenate and check for containment or overlap of data. Also, you can retrieve specific elements or slices within arrays.

Contains Operator (@>)

The @> operator determines whether a left-side array contains a scalar value or array elements on the right side.

@> Syntax

array @> scalar_or_array

Examples

These examples use the @> operator to test whether the left-side array contains all the elements from the right-side array.

Array Containment (True Case)

This example returns true because all right-side elements are in the left-side array.

SELECT ARRAY[1, 4, 3] @> ARRAY[3, 1];

Output: true

Array Containment (False Case)

If the right-side array contains at least one value not present in the left-side array, the query returns false. In this example, the right-side array has one value, 5, not present on the left side.

SELECT ARRAY[1, 4, 3] @> ARRAY[3, 1, 5];

Output: false

Scalar Containment in an Array

This example checks whether a single scalar value is in the left-side array.

SELECT ARRAY[3, 1, 3] @> 1;

Output: true

Contained In Operator (<@)

The <@ operator checks whether a right-side array contains all the elements on the left side.

Syntax

scalar_or_array <@ array

Examples

Array Contained Within Another Array (True Case)

This example returns true because all left-side elements are in the right-side array.

SELECT VARCHAR[]('apples', 'oranges') <@ VARCHAR[]('apples', 'oranges', 'bananas')

Output: true

String Membership Check

<@ and other array operators can check whether individual strings are present in an array. The 'oranges' string is present in the right-side array.

SELECT 'oranges' <@ VARCHAR[]('apples', 'oranges', 'bananas')

Output: true

Overlap Operator (&&)

The overlap operator && determines whether any elements between two arrays are common.

Syntax

array1 && array2

Examples

Check Overlap Between Arrays (True Case)

As long as at least one value is present in both arrays, the && operator returns true. Both of these arrays contain the value 3.

SELECT ARRAY[1 ,2, 3] && ARRAY[3 ,4, 5];

Output: true

Check Overlap Between Arrays (False Case)

Both of these arrays have no values in common, so the && operator returns false.

SELECT ARRAY[1 ,2, 3] && ARRAY[4 ,5, 6];

Output: false

Slice Operator (:)

The slice operator : returns a subarray ranging from a left index to a right index, both of which are optional to specify. If you exclude both indexes, the slice operator returns the full array.

Syntax

array[left_index:right_index]

The slice operator also follows these rules:

• Each index starts at 1.
• If the array or either index value is NULL, the result of slicing is NULL.
• Ranges completely out of array bounds return an empty array. For example, array[1, 2][4:5] = [].
• Sequential slices slice each dimension of multidimensional arrays. For example, ARRAY[ARRAY[1, 2, 3], ARRAY[4, 5, 6]][1:1][2:3] = ARRAY[ARRAY[2,3]].
• More than N sequential slices of an N-dimensional array, for example, three sequential slices on a two-dimensional array return an empty array. For example, ARRAY[1, 2, 3][:][:] = [].
• You cannot combine slicing with the access operator when slicing multidimensional arrays. Any access operator [n] converts to [:n]. For example, Array_Val[4][1:6] would be equivalent to Array_Val[:4][1:6].
• Slicing an array of tuples such as ARRAY[TUPLE<<INT,INT>>(1,2), TUPLE<<INT,INT>>(3,4)][1:1][2:3] slices [1:1] on the array and [2:3] on the tuple elements within the sliced array, and returns the value TUPLE<<INT>>[TUPLE<<INT>>(2)].

Examples

Basic Array Slicing

Slice an array with four numbers starting at index 2 and ending at index 3.

SELECT ARRAY[1 ,2, 3, 4][2:3];

Output:['2','3']

Array Slicing With No Right Index

The query returns all values after the second value because it does not specify an ending index.

SELECT ARRAY[1 ,2, 3, 4][2:];

Output:['2','3','4']

Array Slicing With No Left Index

This query captures a subarray starting at the first index because it does not specify a starting value.

SELECT ARRAY[1 ,2, 3, 4][:3];

Output:['1','2','3']

Array NULL Handling

Filtering with array functions can have different outcomes if they operate on an array containing NULL values or a NULL value of array type.

Array comparison operators, such as @>, <@, and &&, do not follow normal Boolean logic when evaluating NULL values. To evaluate arrays for NULL values, use the filter functions FOR_ALL() or FOR_SOME(). For details about these functions, see Array Filters.

Examples

Evaluate a Single Array With No NULL Values

This example evaluates to false because none of the array values are NULL.

SELECT FOR_SOME(ARRAY[1, 2, 3]) IS NULL;

Output:false

Evaluate a Single Array With NULL Values

This example evaluates to true because the array contains a NULL value.

SELECT FOR_SOME(ARRAY[1, 2, NULL]) IS NULL;

Output:true

Select Only Arrays Containing NULL Values

To further demonstrate array NULL behavior, these examples use this table loaded with a few array values, some of which are NULL or contain NULL values.

CREATE TABLE demo_array_table (
    id INT,
    tags VARCHAR[]
);
INSERT INTO demo_array_table (id, tags) VALUES
    (1, VARCHAR[]('alpha', 'beta', 'gamma')),               -- Regular array
    (2, VARCHAR[]('delta', NULL, 'epsilon')),               -- Array containing a NULL element
    (3, NULL),                                              -- Entirely NULL array
    (4, VARCHAR[]()),                                       -- Empty array
    (5, VARCHAR[](NULL, NULL));                             -- Array containing all NULL elements

In this example, the query uses a FOR_SOME function to filter the rows to return only arrays with NULL values. The output does not include the third row of the table because the row itself is NULL, and is not an array containing NULL values.

SELECT id, tags FROM demo_array_table
    WHERE FOR_SOME(tags) IS NULL;

Output

| id | tags                             |
|----|----------------------------------|
|  2 | ['delta', NULL, 'epsilon']       |
|  5 | [NULL, NULL]                     |

Select NULL Values or Arrays Containing NULL Values

This example includes an additional filter to include any NULL rows and arrays with NULL values.

The example uses the demo_array_table table, which has values that are NULL or contain NULL values.

SELECT id, tags FROM demo_array_table
    WHERE FOR_SOME(tags) IS NULL
    OR tags IS NULL;

Output

| id | tags                         |
|----|------------------------------|
|  3 | NULL                         |
|  5 | [NULL, NULL]                 |
|  2 | ['delta', NULL, 'epsilon']   |

Select Arrays Without NULL Values

This example filters the rows using the FOR_ALL filter function to return only arrays with no NULL values. The output also contains rows with empty arrays.

The example uses the demo_array_table table, which has values that are NULL or contain NULL values.

SELECT id, tags FROM demo_array_table
    WHERE FOR_ALL(tags) IS NOT NULL;

Output

| id | tags                          |
|----|-------------------------------|
|  4 | []                            |
|  1 | ['alpha', 'beta', 'gamma']    |

Select Only Non-Empty Arrays Without NULL Values

To omit empty arrays, you can add a filter to check the array length. The ARRAY_LENGTH function removes any empty arrays.

This example uses the demo_array_table table, which has values that are NULL or contain NULL values.

SELECT id, tags FROM demo_array_table
    WHERE FOR_ALL(tags) IS NOT NULL
    AND ARRAY_LENGTH(tags) > 0;

Output

| id | tags                          |
|----|-------------------------------|
|  1 | ['alpha', 'beta', 'gamma']    |

Multidimensional arrays

Multidimensional arrays are supported. As seen in these examples, each dimension, or length, at each level does not have to be the same. NULL values are allowed at each dimension of an array.

Multidimensional Examples

Related Links

Matrix Functions and Operators

[Tuple Functions and Operators](Tuple Functions and Operators)

Math Functions and Operators

Sorted Aggregate Functions

Array Data Transformation Functions

Data Types

Query Ocient