In GoogleSQL for BigQuery, an array is an ordered list consisting of zero or more
values of the same data type. You can construct arrays of simple data types,
such as INT64
, and complex data types, such as STRUCT
s. The current
exception to this is the ARRAY
data type because arrays of arrays
are not supported. To learn more about the ARRAY
data type, including
NULL
handling, see Array type.
With GoogleSQL, you can construct array literals,
build arrays from subqueries using the
ARRAY
function,
and aggregate values into an array using the
ARRAY_AGG
function.
You can combine arrays using functions like
ARRAY_CONCAT()
, and convert arrays to strings using ARRAY_TO_STRING()
.
Accessing array elements
Consider the following emulated table called Sequences
. This table contains
the column some_numbers
of the ARRAY
data type.
WITH
Sequences AS (
SELECT [0, 1, 1, 2, 3, 5] AS some_numbers UNION ALL
SELECT [2, 4, 8, 16, 32] UNION ALL
SELECT [5, 10]
)
SELECT * FROM Sequences
/*---------------------*
| some_numbers |
+---------------------+
| [0, 1, 1, 2, 3, 5] |
| [2, 4, 8, 16, 32] |
| [5, 10] |
*---------------------*/
To access array elements in the some_numbers
column, specify which
type of indexing you want to use:
either index
or OFFSET(index)
for
zero-based indexes, or ORDINAL(index)
for
one-based indexes.
For example:
SELECT
some_numbers,
some_numbers[0] AS index_0,
some_numbers[OFFSET(1)] AS offset_1,
some_numbers[ORDINAL(1)] AS ordinal_1
FROM Sequences
/*--------------------+---------+----------+-----------*
| some_numbers | index_0 | offset_1 | ordinal_1 |
+--------------------+---------+----------+-----------+
| [0, 1, 1, 2, 3, 5] | 0 | 1 | 0 |
| [2, 4, 8, 16, 32] | 2 | 4 | 2 |
| [5, 10] | 5 | 10 | 5 |
*--------------------+---------+----------+-----------*/
Finding lengths
The ARRAY_LENGTH
function returns the length of an array.
WITH Sequences AS
(SELECT [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT [5, 10] AS some_numbers)
SELECT some_numbers,
ARRAY_LENGTH(some_numbers) AS len
FROM Sequences;
/*--------------------+--------*
| some_numbers | len |
+--------------------+--------+
| [0, 1, 1, 2, 3, 5] | 6 |
| [2, 4, 8, 16, 32] | 5 |
| [5, 10] | 2 |
*--------------------+--------*/
Converting elements in an array to rows in a table
To convert an ARRAY
into a set of rows, also known as "flattening," use the
UNNEST
operator. UNNEST
takes an ARRAY
and returns a table with a single row for
each element in the ARRAY
.
Because UNNEST
destroys the order of the ARRAY
elements, you may
wish to restore order to the table. To do so, use the optional WITH OFFSET
clause to return an additional column with the offset for each array element,
then use the ORDER BY
clause to order the rows by their offset.
Example
SELECT *
FROM UNNEST(['foo', 'bar', 'baz', 'qux', 'corge', 'garply', 'waldo', 'fred'])
AS element
WITH OFFSET AS offset
ORDER BY offset;
/*----------+--------*
| element | offset |
+----------+--------+
| foo | 0 |
| bar | 1 |
| baz | 2 |
| qux | 3 |
| corge | 4 |
| garply | 5 |
| waldo | 6 |
| fred | 7 |
*----------+--------*/
To flatten an entire column of ARRAY
s while preserving the values
of the other columns in each row, use a correlated
cross join to join the table containing the
ARRAY
column to the UNNEST
output of that ARRAY
column.
With a correlated join, the UNNEST
operator
references the ARRAY
typed column from each row in the source table, which
appears previously in the FROM
clause. For each row N
in the source table,
UNNEST
flattens the ARRAY
from row N
into a set of rows containing the
ARRAY
elements, and then the cross join joins this new set of rows with the
single row N
from the source table.
Examples
The following example uses UNNEST
to return a row for each element in the array column. Because of the
CROSS JOIN
, the id
column contains the id
values for the row in
Sequences
that contains each number.
WITH Sequences AS
(SELECT 1 AS id, [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT 2 AS id, [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT 3 AS id, [5, 10] AS some_numbers)
SELECT id, flattened_numbers
FROM Sequences
CROSS JOIN UNNEST(Sequences.some_numbers) AS flattened_numbers;
/*------+-------------------*
| id | flattened_numbers |
+------+-------------------+
| 1 | 0 |
| 1 | 1 |
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 5 |
| 2 | 2 |
| 2 | 4 |
| 2 | 8 |
| 2 | 16 |
| 2 | 32 |
| 3 | 5 |
| 3 | 10 |
*------+-------------------*/
Note that for correlated cross joins the UNNEST
operator is optional and the
CROSS JOIN
can be expressed as a comma cross join. Using this shorthand
notation, the previous example is consolidated as follows:
WITH Sequences AS
(SELECT 1 AS id, [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT 2 AS id, [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT 3 AS id, [5, 10] AS some_numbers)
SELECT id, flattened_numbers
FROM Sequences, Sequences.some_numbers AS flattened_numbers;
/*------+-------------------*
| id | flattened_numbers |
+------+-------------------+
| 1 | 0 |
| 1 | 1 |
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 5 |
| 2 | 2 |
| 2 | 4 |
| 2 | 8 |
| 2 | 16 |
| 2 | 32 |
| 3 | 5 |
| 3 | 10 |
*------+-------------------*/
Querying nested arrays
If a table contains an ARRAY
of STRUCT
s, you can
flatten the ARRAY
to query the fields of the STRUCT
.
You can also flatten ARRAY
type fields of STRUCT
values.
Querying STRUCT
elements in an array
The following example uses UNNEST
with CROSS JOIN
to flatten an ARRAY
of
STRUCT
s.
WITH Races AS (
SELECT "800M" AS race,
[STRUCT("Rudisha" AS name, [23.4, 26.3, 26.4, 26.1] AS laps),
STRUCT("Makhloufi" AS name, [24.5, 25.4, 26.6, 26.1] AS laps),
STRUCT("Murphy" AS name, [23.9, 26.0, 27.0, 26.0] AS laps),
STRUCT("Bosse" AS name, [23.6, 26.2, 26.5, 27.1] AS laps),
STRUCT("Rotich" AS name, [24.7, 25.6, 26.9, 26.4] AS laps),
STRUCT("Lewandowski" AS name, [25.0, 25.7, 26.3, 27.2] AS laps),
STRUCT("Kipketer" AS name, [23.2, 26.1, 27.3, 29.4] AS laps),
STRUCT("Berian" AS name, [23.7, 26.1, 27.0, 29.3] AS laps)]
AS participants)
SELECT
race,
participant
FROM Races AS r
CROSS JOIN UNNEST(r.participants) AS participant;
/*------+---------------------------------------*
| race | participant |
+------+---------------------------------------+
| 800M | {Rudisha, [23.4, 26.3, 26.4, 26.1]} |
| 800M | {Makhloufi, [24.5, 25.4, 26.6, 26.1]} |
| 800M | {Murphy, [23.9, 26, 27, 26]} |
| 800M | {Bosse, [23.6, 26.2, 26.5, 27.1]} |
| 800M | {Rotich, [24.7, 25.6, 26.9, 26.4]} |
| 800M | {Lewandowski, [25, 25.7, 26.3, 27.2]} |
| 800M | {Kipketer, [23.2, 26.1, 27.3, 29.4]} |
| 800M | {Berian, [23.7, 26.1, 27, 29.3]} |
*------+---------------------------------------*/
You can find specific information from repeated fields. For example, the following query returns the fastest racer in an 800M race.
Example
WITH Races AS (
SELECT "800M" AS race,
[STRUCT("Rudisha" AS name, [23.4, 26.3, 26.4, 26.1] AS laps),
STRUCT("Makhloufi" AS name, [24.5, 25.4, 26.6, 26.1] AS laps),
STRUCT("Murphy" AS name, [23.9, 26.0, 27.0, 26.0] AS laps),
STRUCT("Bosse" AS name, [23.6, 26.2, 26.5, 27.1] AS laps),
STRUCT("Rotich" AS name, [24.7, 25.6, 26.9, 26.4] AS laps),
STRUCT("Lewandowski" AS name, [25.0, 25.7, 26.3, 27.2] AS laps),
STRUCT("Kipketer" AS name, [23.2, 26.1, 27.3, 29.4] AS laps),
STRUCT("Berian" AS name, [23.7, 26.1, 27.0, 29.3] AS laps)]
AS participants)
SELECT
race,
(SELECT name
FROM UNNEST(participants)
ORDER BY (
SELECT SUM(duration)
FROM UNNEST(laps) AS duration) ASC
LIMIT 1) AS fastest_racer
FROM Races;
/*------+---------------*
| race | fastest_racer |
+------+---------------+
| 800M | Rudisha |
*------+---------------*/
Querying ARRAY
-type fields in a struct
You can also get information from nested repeated fields. For example, the following statement returns the runner who had the fastest lap in an 800M race.
WITH Races AS (
SELECT "800M" AS race,
[STRUCT("Rudisha" AS name, [23.4, 26.3, 26.4, 26.1] AS laps),
STRUCT("Makhloufi" AS name, [24.5, 25.4, 26.6, 26.1] AS laps),
STRUCT("Murphy" AS name, [23.9, 26.0, 27.0, 26.0] AS laps),
STRUCT("Bosse" AS name, [23.6, 26.2, 26.5, 27.1] AS laps),
STRUCT("Rotich" AS name, [24.7, 25.6, 26.9, 26.4] AS laps),
STRUCT("Lewandowski" AS name, [25.0, 25.7, 26.3, 27.2] AS laps),
STRUCT("Kipketer" AS name, [23.2, 26.1, 27.3, 29.4] AS laps),
STRUCT("Berian" AS name, [23.7, 26.1, 27.0, 29.3] AS laps)]
AS participants)
SELECT
race,
(SELECT name
FROM UNNEST(participants),
UNNEST(laps) AS duration
ORDER BY duration ASC LIMIT 1) AS runner_with_fastest_lap
FROM Races;
/*------+-------------------------*
| race | runner_with_fastest_lap |
+------+-------------------------+
| 800M | Kipketer |
*------+-------------------------*/
Notice that the preceding query uses the comma operator (,
) to perform an
implicit CROSS JOIN
. It is equivalent to the following example, which uses
an explicit CROSS JOIN
.
WITH Races AS (
SELECT "800M" AS race,
[STRUCT("Rudisha" AS name, [23.4, 26.3, 26.4, 26.1] AS laps),
STRUCT("Makhloufi" AS name, [24.5, 25.4, 26.6, 26.1] AS laps),
STRUCT("Murphy" AS name, [23.9, 26.0, 27.0, 26.0] AS laps),
STRUCT("Bosse" AS name, [23.6, 26.2, 26.5, 27.1] AS laps),
STRUCT("Rotich" AS name, [24.7, 25.6, 26.9, 26.4] AS laps),
STRUCT("Lewandowski" AS name, [25.0, 25.7, 26.3, 27.2] AS laps),
STRUCT("Kipketer" AS name, [23.2, 26.1, 27.3, 29.4] AS laps),
STRUCT("Berian" AS name, [23.7, 26.1, 27.0, 29.3] AS laps)]
AS participants)
SELECT
race,
(SELECT name
FROM UNNEST(participants)
CROSS JOIN UNNEST(laps) AS duration
ORDER BY duration ASC LIMIT 1) AS runner_with_fastest_lap
FROM Races;
/*------+-------------------------*
| race | runner_with_fastest_lap |
+------+-------------------------+
| 800M | Kipketer |
*------+-------------------------*/
Flattening arrays with a CROSS JOIN
excludes rows that have empty
or NULL arrays. If you want to include these rows, use a LEFT JOIN
.
WITH Races AS (
SELECT "800M" AS race,
[STRUCT("Rudisha" AS name, [23.4, 26.3, 26.4, 26.1] AS laps),
STRUCT("Makhloufi" AS name, [24.5, 25.4, 26.6, 26.1] AS laps),
STRUCT("Murphy" AS name, [23.9, 26.0, 27.0, 26.0] AS laps),
STRUCT("Bosse" AS name, [23.6, 26.2, 26.5, 27.1] AS laps),
STRUCT("Rotich" AS name, [24.7, 25.6, 26.9, 26.4] AS laps),
STRUCT("Lewandowski" AS name, [25.0, 25.7, 26.3, 27.2] AS laps),
STRUCT("Kipketer" AS name, [23.2, 26.1, 27.3, 29.4] AS laps),
STRUCT("Berian" AS name, [23.7, 26.1, 27.0, 29.3] AS laps),
STRUCT("Nathan" AS name, ARRAY<FLOAT64>[] AS laps),
STRUCT("David" AS name, NULL AS laps)]
AS participants)
SELECT
name, sum(duration) AS finish_time
FROM Races CROSS JOIN Races.participants LEFT JOIN participants.laps AS duration
GROUP BY name;
/*-------------+--------------------*
| name | finish_time |
+-------------+--------------------+
| Murphy | 102.9 |
| Rudisha | 102.19999999999999 |
| David | NULL |
| Rotich | 103.6 |
| Makhloufi | 102.6 |
| Berian | 106.1 |
| Bosse | 103.4 |
| Kipketer | 106 |
| Nathan | NULL |
| Lewandowski | 104.2 |
*-------------+--------------------*/
Constructing arrays
You can construct an array using array literals or array functions. To learn more about constructing arrays, see Array type.
Creating arrays from subqueries
A common task when working with arrays is turning a subquery result into an
array. In GoogleSQL, you can accomplish this using the
ARRAY()
function.
For example, consider the following operation on the Sequences
table:
WITH Sequences AS
(SELECT [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT [5, 10] AS some_numbers)
SELECT some_numbers,
ARRAY(SELECT x * 2
FROM UNNEST(some_numbers) AS x) AS doubled
FROM Sequences;
/*--------------------+---------------------*
| some_numbers | doubled |
+--------------------+---------------------+
| [0, 1, 1, 2, 3, 5] | [0, 2, 2, 4, 6, 10] |
| [2, 4, 8, 16, 32] | [4, 8, 16, 32, 64] |
| [5, 10] | [10, 20] |
*--------------------+---------------------*/
This example starts with a table named Sequences. This table contains a column,
some_numbers
, of type ARRAY<INT64>
.
The query itself contains a subquery. This subquery selects each row in the
some_numbers
column and uses
UNNEST
to return the
array as a set of rows. Next, it multiplies each value by two, and then
re-combines the rows back into an array using the ARRAY()
operator.
Filtering arrays
The following example uses a WHERE
clause in the ARRAY()
operator's subquery
to filter the returned rows.
WITH Sequences AS
(SELECT [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT [5, 10] AS some_numbers)
SELECT
ARRAY(SELECT x * 2
FROM UNNEST(some_numbers) AS x
WHERE x < 5) AS doubled_less_than_five
FROM Sequences;
/*------------------------*
| doubled_less_than_five |
+------------------------+
| [0, 2, 2, 4, 6] |
| [4, 8] |
| [] |
*------------------------*/
Notice that the third row contains an empty array, because the elements in the
corresponding original row ([5, 10]
) did not meet the filter requirement of
x < 5
.
You can also filter arrays by using SELECT DISTINCT
to return only
unique elements within an array.
WITH Sequences AS
(SELECT [0, 1, 1, 2, 3, 5] AS some_numbers)
SELECT ARRAY(SELECT DISTINCT x
FROM UNNEST(some_numbers) AS x) AS unique_numbers
FROM Sequences;
/*-----------------*
| unique_numbers |
+-----------------+
| [0, 1, 2, 3, 5] |
*-----------------*/
You can also filter rows of arrays by using the
IN
keyword. This
keyword filters rows containing arrays by determining if a specific
value matches an element in the array.
WITH Sequences AS
(SELECT [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT [5, 10] AS some_numbers)
SELECT
ARRAY(SELECT x
FROM UNNEST(some_numbers) AS x
WHERE 2 IN UNNEST(some_numbers)) AS contains_two
FROM Sequences;
/*--------------------*
| contains_two |
+--------------------+
| [0, 1, 1, 2, 3, 5] |
| [2, 4, 8, 16, 32] |
| [] |
*--------------------*/
Notice again that the third row contains an empty array, because the array in
the corresponding original row ([5, 10]
) did not contain 2
.
Scanning arrays
To check if an array contains a specific value, use the IN
operator with UNNEST
. To check if an array contains a value
matching a condition, use the EXISTS
operator with
UNNEST
.
Scanning for specific values
To scan an array for a specific value, use the IN
operator with UNNEST
.
Example
The following example returns true
if the array contains the number 2.
SELECT 2 IN UNNEST([0, 1, 1, 2, 3, 5]) AS contains_value;
/*----------------*
| contains_value |
+----------------+
| true |
*----------------*/
To return the rows of a table where the array column contains a specific value,
filter the results of IN UNNEST
using the WHERE
clause.
Example
The following example returns the id
value for the rows where the array
column contains the value 2.
WITH Sequences AS
(SELECT 1 AS id, [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT 2 AS id, [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT 3 AS id, [5, 10] AS some_numbers)
SELECT id AS matching_rows
FROM Sequences
WHERE 2 IN UNNEST(Sequences.some_numbers)
ORDER BY matching_rows;
/*---------------*
| matching_rows |
+---------------+
| 1 |
| 2 |
*---------------*/
Scanning for values that satisfy a condition
To scan an array for values that match a condition, use UNNEST
to return a
table of the elements in the array, use WHERE
to filter the resulting table in
a subquery, and use EXISTS
to check if the filtered table contains any rows.
Example
The following example returns the id
value for the rows where the array
column contains values greater than 5.
WITH
Sequences AS (
SELECT 1 AS id, [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL
SELECT 2 AS id, [2, 4, 8, 16, 32] AS some_numbers
UNION ALL
SELECT 3 AS id, [5, 10] AS some_numbers
)
SELECT id AS matching_rows
FROM Sequences
WHERE EXISTS(SELECT * FROM UNNEST(some_numbers) AS x WHERE x > 5);
/*---------------*
| matching_rows |
+---------------+
| 2 |
| 3 |
*---------------*/
Scanning for STRUCT
field values that satisfy a condition
To search an array of STRUCT
s for a field whose value matches a condition, use
UNNEST
to return a table with a column for each STRUCT
field, then filter
non-matching rows from the table using WHERE EXISTS
.
Example
The following example returns the rows where the array column contains a
STRUCT
whose field b
has a value greater than 3.
WITH
Sequences AS (
SELECT 1 AS id, [STRUCT(0 AS a, 1 AS b)] AS some_numbers
UNION ALL
SELECT 2 AS id, [STRUCT(2 AS a, 4 AS b)] AS some_numbers
UNION ALL
SELECT 3 AS id, [STRUCT(5 AS a, 3 AS b), STRUCT(7 AS a, 4 AS b)] AS some_numbers
)
SELECT id AS matching_rows
FROM Sequences
WHERE EXISTS(SELECT 1 FROM UNNEST(some_numbers) WHERE b > 3);
/*---------------*
| matching_rows |
+---------------+
| 2 |
| 3 |
*---------------*/
Arrays and aggregation
With GoogleSQL, you can aggregate values into an array using
ARRAY_AGG()
.
WITH Fruits AS
(SELECT "apple" AS fruit
UNION ALL SELECT "pear" AS fruit
UNION ALL SELECT "banana" AS fruit)
SELECT ARRAY_AGG(fruit) AS fruit_basket
FROM Fruits;
/*-----------------------*
| fruit_basket |
+-----------------------+
| [apple, pear, banana] |
*-----------------------*/
The array returned by ARRAY_AGG()
is in an arbitrary order, since the order in
which the function concatenates values is not guaranteed. To order the array
elements, use ORDER BY
. For example:
WITH Fruits AS
(SELECT "apple" AS fruit
UNION ALL SELECT "pear" AS fruit
UNION ALL SELECT "banana" AS fruit)
SELECT ARRAY_AGG(fruit ORDER BY fruit) AS fruit_basket
FROM Fruits;
/*-----------------------*
| fruit_basket |
+-----------------------+
| [apple, banana, pear] |
*-----------------------*/
You can also apply aggregate functions such as SUM()
to the elements in an
array. For example, the following query returns the sum of array elements for
each row of the Sequences
table.
WITH Sequences AS
(SELECT [0, 1, 1, 2, 3, 5] AS some_numbers
UNION ALL SELECT [2, 4, 8, 16, 32] AS some_numbers
UNION ALL SELECT [5, 10] AS some_numbers)
SELECT some_numbers,
(SELECT SUM(x)
FROM UNNEST(s.some_numbers) AS x) AS sums
FROM Sequences AS s;
/*--------------------+------*
| some_numbers | sums |
+--------------------+------+
| [0, 1, 1, 2, 3, 5] | 12 |
| [2, 4, 8, 16, 32] | 62 |
| [5, 10] | 15 |
*--------------------+------*/
GoogleSQL also supports an aggregate function, ARRAY_CONCAT_AGG()
,
which concatenates the elements of an array column across rows.
WITH Aggregates AS
(SELECT [1,2] AS numbers
UNION ALL SELECT [3,4] AS numbers
UNION ALL SELECT [5, 6] AS numbers)
SELECT ARRAY_CONCAT_AGG(numbers) AS count_to_six_agg
FROM Aggregates;
/*--------------------------------------------------*
| count_to_six_agg |
+--------------------------------------------------+
| [1, 2, 3, 4, 5, 6] |
*--------------------------------------------------*/
Converting arrays to strings
The ARRAY_TO_STRING()
function allows you to convert an ARRAY<STRING>
to a
single STRING
value or an ARRAY<BYTES>
to a single BYTES
value where the
resulting value is the ordered concatenation of the array elements.
The second argument is the separator that the function will insert between inputs to produce the output; this second argument must be of the same type as the elements of the first argument.
Example:
WITH Words AS
(SELECT ["Hello", "World"] AS greeting)
SELECT ARRAY_TO_STRING(greeting, " ") AS greetings
FROM Words;
/*-------------*
| greetings |
+-------------+
| Hello World |
*-------------*/
The optional third argument takes the place of NULL
values in the input
array.
If you omit this argument, then the function ignores
NULL
array elements.If you provide an empty string, the function inserts a separator for
NULL
array elements.
Example:
SELECT
ARRAY_TO_STRING(arr, ".", "N") AS non_empty_string,
ARRAY_TO_STRING(arr, ".", "") AS empty_string,
ARRAY_TO_STRING(arr, ".") AS omitted
FROM (SELECT ["a", NULL, "b", NULL, "c", NULL] AS arr);
/*------------------+--------------+---------*
| non_empty_string | empty_string | omitted |
+------------------+--------------+---------+
| a.N.b.N.c.N | a..b..c. | a.b.c |
*------------------+--------------+---------*/
Combining arrays
In some cases, you might want to combine multiple arrays into a single array.
You can accomplish this using the ARRAY_CONCAT()
function.
SELECT ARRAY_CONCAT([1, 2], [3, 4], [5, 6]) AS count_to_six;
/*--------------------------------------------------*
| count_to_six |
+--------------------------------------------------+
| [1, 2, 3, 4, 5, 6] |
*--------------------------------------------------*/
Updating arrays
Consider the following table called arrays_table
. The first column in the
table is an array of integers and the second column contains two nested arrays
of integers.
WITH arrays_table AS (
SELECT
[1, 2] AS regular_array,
STRUCT([10, 20] AS first_array, [100, 200] AS second_array) AS nested_arrays
UNION ALL SELECT
[3, 4] AS regular_array,
STRUCT([30, 40] AS first_array, [300, 400] AS second_array) AS nested_arrays
)
SELECT * FROM arrays_table;
/*---------------*---------------------------*----------------------------*
| regular_array | nested_arrays.first_array | nested_arrays.second_array |
+---------------+---------------------------+----------------------------+
| [1, 2] | [10, 20] | [100, 200] |
| [3, 4] | [30, 40] | [130, 400] |
*---------------*---------------------------*----------------------------*/
You can update arrays in a table by using the UPDATE
statement. The following
example inserts the number 5 into the regular_array
column,
and inserts the elements from the first_array
field of the nested_arrays
column into the second_array
field:
UPDATE
arrays_table
SET
regular_array = ARRAY_CONCAT(regular_array, [5]),
nested_arrays.second_array = ARRAY_CONCAT(nested_arrays.second_array,
nested_arrays.first_array)
WHERE TRUE;
SELECT * FROM arrays_table;
/*---------------*---------------------------*----------------------------*
| regular_array | nested_arrays.first_array | nested_arrays.second_array |
+---------------+---------------------------+----------------------------+
| [1, 2, 5] | [10, 20] | [100, 200, 10, 20] |
| [3, 4, 5] | [30, 40] | [130, 400, 30, 40] |
*---------------*---------------------------*----------------------------*/
Zipping arrays
Given two arrays of equal size, you can merge them into a single array consisting of pairs of elements from input arrays, taken from their corresponding positions. This operation is sometimes called zipping.
You can zip arrays with UNNEST
and WITH OFFSET
. In this example, each
value pair is stored as a STRUCT
in an array.
WITH
Combinations AS (
SELECT
['a', 'b'] AS letters,
[1, 2, 3] AS numbers
)
SELECT
ARRAY(
SELECT AS STRUCT
letters[SAFE_OFFSET(index)] AS letter,
numbers[SAFE_OFFSET(index)] AS number
FROM Combinations
CROSS JOIN
UNNEST(
GENERATE_ARRAY(
0,
LEAST(ARRAY_LENGTH(letters), ARRAY_LENGTH(numbers)) - 1)) AS index
ORDER BY index
);
/*------------------------------*
| pairs |
+------------------------------+
| [{ letter: "a", number: 1 }, |
| { letter: "b", number: 2 }] |
*------------------------------*/
You can use input arrays of different lengths as long as the first array is equal to or less than the length of the second array. The zipped array will be the length of the shortest input array.
To get a zipped array that includes all the elements even when the input arrays
are different lengths, change LEAST
to GREATEST
. Elements of either array
that have no associated element in the other array will be paired with NULL
.
WITH
Combinations AS (
SELECT
['a', 'b'] AS letters,
[1, 2, 3] AS numbers
)
SELECT
ARRAY(
SELECT AS STRUCT
letters[SAFE_OFFSET(index)] AS letter,
numbers[SAFE_OFFSET(index)] AS number
FROM Combinations
CROSS JOIN
UNNEST(
GENERATE_ARRAY(
0,
GREATEST(ARRAY_LENGTH(letters), ARRAY_LENGTH(numbers)) - 1)) AS index
ORDER BY index
);
/*-------------------------------*
| pairs |
+-------------------------------+
| [{ letter: "a", number: 1 }, |
| { letter: "b", number: 2 }, |
| { letter: null, number: 3 }] |
*-------------------------------*/
Building arrays of arrays
GoogleSQL does not support building
arrays of arrays
directly. Instead, you must create an array of structs, with each struct
containing a field of type ARRAY
. To illustrate this, consider the following
Points
table:
/*----------*
| point |
+----------+
| [1, 5] |
| [2, 8] |
| [3, 7] |
| [4, 1] |
| [5, 7] |
*----------*/
Now, let's say you wanted to create an array consisting of each point
in the
Points
table. To accomplish this, wrap the array returned from each row in a
STRUCT
, as shown below.
WITH Points AS
(SELECT [1, 5] AS point
UNION ALL SELECT [2, 8] AS point
UNION ALL SELECT [3, 7] AS point
UNION ALL SELECT [4, 1] AS point
UNION ALL SELECT [5, 7] AS point)
SELECT ARRAY(
SELECT STRUCT(point)
FROM Points)
AS coordinates;
/*-------------------*
| coordinates |
+-------------------+
| [{point: [1,5]}, |
| {point: [2,8]}, |
| {point: [5,7]}, |
| {point: [3,7]}, |
| {point: [4,1]}] |
*-------------------*/