<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>8.15. Arrays</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="datatype-json.html" title="8.14. JSON Types" /><link rel="next" href="rowtypes.html" title="8.16. Composite Types" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">8.15. Arrays</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="datatype-json.html" title="8.14. JSON Types">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="datatype.html" title="Chapter 8. Data Types">Up</a></td><th width="60%" align="center">Chapter 8. Data Types</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="rowtypes.html" title="8.16. Composite Types">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="ARRAYS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">8.15. Arrays</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="arrays.html#ARRAYS-DECLARATION">8.15.1. Declaration of Array Types</a></span></dt><dt><span class="sect2"><a href="arrays.html#ARRAYS-INPUT">8.15.2. Array Value Input</a></span></dt><dt><span class="sect2"><a href="arrays.html#ARRAYS-ACCESSING">8.15.3. Accessing Arrays</a></span></dt><dt><span class="sect2"><a href="arrays.html#ARRAYS-MODIFYING">8.15.4. Modifying Arrays</a></span></dt><dt><span class="sect2"><a href="arrays.html#ARRAYS-SEARCHING">8.15.5. Searching in Arrays</a></span></dt><dt><span class="sect2"><a href="arrays.html#ARRAYS-IO">8.15.6. Array Input and Output Syntax</a></span></dt></dl></div><a id="id-1.5.7.23.2" class="indexterm"></a><p>
<span class="productname">PostgreSQL</span> allows columns of a table to be
defined as variable-length multidimensional arrays. Arrays of any
built-in or user-defined base type, enum type, composite type, range type,
or domain can be created.
</p><div class="sect2" id="ARRAYS-DECLARATION"><div class="titlepage"><div><div><h3 class="title">8.15.1. Declaration of Array Types</h3></div></div></div><a id="id-1.5.7.23.4.2" class="indexterm"></a><p>
To illustrate the use of array types, we create this table:
</p><pre class="programlisting">
CREATE TABLE sal_emp (
name text,
pay_by_quarter integer[],
schedule text[][]
);
</pre><p>
As shown, an array data type is named by appending square brackets
(<code class="literal">[]</code>) to the data type name of the array elements. The
above command will create a table named
<code class="structname">sal_emp</code> with a column of type
<code class="type">text</code> (<code class="structfield">name</code>), a
one-dimensional array of type <code class="type">integer</code>
(<code class="structfield">pay_by_quarter</code>), which represents the
employee's salary by quarter, and a two-dimensional array of
<code class="type">text</code> (<code class="structfield">schedule</code>), which
represents the employee's weekly schedule.
</p><p>
The syntax for <code class="command">CREATE TABLE</code> allows the exact size of
arrays to be specified, for example:
</p><pre class="programlisting">
CREATE TABLE tictactoe (
squares integer[3][3]
);
</pre><p>
However, the current implementation ignores any supplied array size
limits, i.e., the behavior is the same as for arrays of unspecified
length.
</p><p>
The current implementation does not enforce the declared
number of dimensions either. Arrays of a particular element type are
all considered to be of the same type, regardless of size or number
of dimensions. So, declaring the array size or number of dimensions in
<code class="command">CREATE TABLE</code> is simply documentation; it does not
affect run-time behavior.
</p><p>
An alternative syntax, which conforms to the SQL standard by using
the keyword <code class="literal">ARRAY</code>, can be used for one-dimensional arrays.
<code class="structfield">pay_by_quarter</code> could have been defined
as:
</p><pre class="programlisting">
pay_by_quarter integer ARRAY[4],
</pre><p>
Or, if no array size is to be specified:
</p><pre class="programlisting">
pay_by_quarter integer ARRAY,
</pre><p>
As before, however, <span class="productname">PostgreSQL</span> does not enforce the
size restriction in any case.
</p></div><div class="sect2" id="ARRAYS-INPUT"><div class="titlepage"><div><div><h3 class="title">8.15.2. Array Value Input</h3></div></div></div><a id="id-1.5.7.23.5.2" class="indexterm"></a><p>
To write an array value as a literal constant, enclose the element
values within curly braces and separate them by commas. (If you
know C, this is not unlike the C syntax for initializing
structures.) You can put double quotes around any element value,
and must do so if it contains commas or curly braces. (More
details appear below.) Thus, the general format of an array
constant is the following:
</p><pre class="synopsis">
'{ <em class="replaceable"><code>val1</code></em> <em class="replaceable"><code>delim</code></em> <em class="replaceable"><code>val2</code></em> <em class="replaceable"><code>delim</code></em> ... }'
</pre><p>
where <em class="replaceable"><code>delim</code></em> is the delimiter character
for the type, as recorded in its <code class="literal">pg_type</code> entry.
Among the standard data types provided in the
<span class="productname">PostgreSQL</span> distribution, all use a comma
(<code class="literal">,</code>), except for type <code class="type">box</code> which uses a semicolon
(<code class="literal">;</code>). Each <em class="replaceable"><code>val</code></em> is
either a constant of the array element type, or a subarray. An example
of an array constant is:
</p><pre class="programlisting">
'{{1,2,3},{4,5,6},{7,8,9}}'
</pre><p>
This constant is a two-dimensional, 3-by-3 array consisting of
three subarrays of integers.
</p><p>
To set an element of an array constant to NULL, write <code class="literal">NULL</code>
for the element value. (Any upper- or lower-case variant of
<code class="literal">NULL</code> will do.) If you want an actual string value
<span class="quote">“<span class="quote">NULL</span>”</span>, you must put double quotes around it.
</p><p>
(These kinds of array constants are actually only a special case of
the generic type constants discussed in <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-CONSTANTS-GENERIC" title="4.1.2.7. Constants of Other Types">Section 4.1.2.7</a>. The constant is initially
treated as a string and passed to the array input conversion
routine. An explicit type specification might be necessary.)
</p><p>
Now we can show some <code class="command">INSERT</code> statements:
</p><pre class="programlisting">
INSERT INTO sal_emp
VALUES ('Bill',
'{10000, 10000, 10000, 10000}',
'{{"meeting", "lunch"}, {"training", "presentation"}}');
INSERT INTO sal_emp
VALUES ('Carol',
'{20000, 25000, 25000, 25000}',
'{{"breakfast", "consulting"}, {"meeting", "lunch"}}');
</pre><p>
</p><p>
The result of the previous two inserts looks like this:
</p><pre class="programlisting">
SELECT * FROM sal_emp;
name | pay_by_quarter | schedule
-------+---------------------------+-------------------------------------------
Bill | {10000,10000,10000,10000} | {{meeting,lunch},{training,presentation}}
Carol | {20000,25000,25000,25000} | {{breakfast,consulting},{meeting,lunch}}
(2 rows)
</pre><p>
</p><p>
Multidimensional arrays must have matching extents for each
dimension. A mismatch causes an error, for example:
</p><pre class="programlisting">
INSERT INTO sal_emp
VALUES ('Bill',
'{10000, 10000, 10000, 10000}',
'{{"meeting", "lunch"}, {"meeting"}}');
ERROR: multidimensional arrays must have array expressions with matching dimensions
</pre><p>
</p><p>
The <code class="literal">ARRAY</code> constructor syntax can also be used:
</p><pre class="programlisting">
INSERT INTO sal_emp
VALUES ('Bill',
ARRAY[10000, 10000, 10000, 10000],
ARRAY[['meeting', 'lunch'], ['training', 'presentation']]);
INSERT INTO sal_emp
VALUES ('Carol',
ARRAY[20000, 25000, 25000, 25000],
ARRAY[['breakfast', 'consulting'], ['meeting', 'lunch']]);
</pre><p>
Notice that the array elements are ordinary SQL constants or
expressions; for instance, string literals are single quoted, instead of
double quoted as they would be in an array literal. The <code class="literal">ARRAY</code>
constructor syntax is discussed in more detail in
<a class="xref" href="sql-expressions.html#SQL-SYNTAX-ARRAY-CONSTRUCTORS" title="4.2.12. Array Constructors">Section 4.2.12</a>.
</p></div><div class="sect2" id="ARRAYS-ACCESSING"><div class="titlepage"><div><div><h3 class="title">8.15.3. Accessing Arrays</h3></div></div></div><a id="id-1.5.7.23.6.2" class="indexterm"></a><p>
Now, we can run some queries on the table.
First, we show how to access a single element of an array.
This query retrieves the names of the employees whose pay changed in
the second quarter:
</p><pre class="programlisting">
SELECT name FROM sal_emp WHERE pay_by_quarter[1] <> pay_by_quarter[2];
name
-------
Carol
(1 row)
</pre><p>
The array subscript numbers are written within square brackets.
By default <span class="productname">PostgreSQL</span> uses a
one-based numbering convention for arrays, that is,
an array of <em class="replaceable"><code>n</code></em> elements starts with <code class="literal">array[1]</code> and
ends with <code class="literal">array[<em class="replaceable"><code>n</code></em>]</code>.
</p><p>
This query retrieves the third quarter pay of all employees:
</p><pre class="programlisting">
SELECT pay_by_quarter[3] FROM sal_emp;
pay_by_quarter
----------------
10000
25000
(2 rows)
</pre><p>
</p><p>
We can also access arbitrary rectangular slices of an array, or
subarrays. An array slice is denoted by writing
<code class="literal"><em class="replaceable"><code>lower-bound</code></em>:<em class="replaceable"><code>upper-bound</code></em></code>
for one or more array dimensions. For example, this query retrieves the first
item on Bill's schedule for the first two days of the week:
</p><pre class="programlisting">
SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';
schedule
------------------------
{{meeting},{training}}
(1 row)
</pre><p>
If any dimension is written as a slice, i.e., contains a colon, then all
dimensions are treated as slices. Any dimension that has only a single
number (no colon) is treated as being from 1
to the number specified. For example, <code class="literal">[2]</code> is treated as
<code class="literal">[1:2]</code>, as in this example:
</p><pre class="programlisting">
SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill';
schedule
-------------------------------------------
{{meeting,lunch},{training,presentation}}
(1 row)
</pre><p>
To avoid confusion with the non-slice case, it's best to use slice syntax
for all dimensions, e.g., <code class="literal">[1:2][1:1]</code>, not <code class="literal">[2][1:1]</code>.
</p><p>
It is possible to omit the <em class="replaceable"><code>lower-bound</code></em> and/or
<em class="replaceable"><code>upper-bound</code></em> of a slice specifier; the missing
bound is replaced by the lower or upper limit of the array's subscripts.
For example:
</p><pre class="programlisting">
SELECT schedule[:2][2:] FROM sal_emp WHERE name = 'Bill';
schedule
------------------------
{{lunch},{presentation}}
(1 row)
SELECT schedule[:][1:1] FROM sal_emp WHERE name = 'Bill';
schedule
------------------------
{{meeting},{training}}
(1 row)
</pre><p>
</p><p>
An array subscript expression will return null if either the array itself or
any of the subscript expressions are null. Also, null is returned if a
subscript is outside the array bounds (this case does not raise an error).
For example, if <code class="literal">schedule</code>
currently has the dimensions <code class="literal">[1:3][1:2]</code> then referencing
<code class="literal">schedule[3][3]</code> yields NULL. Similarly, an array reference
with the wrong number of subscripts yields a null rather than an error.
</p><p>
An array slice expression likewise yields null if the array itself or
any of the subscript expressions are null. However, in other
cases such as selecting an array slice that
is completely outside the current array bounds, a slice expression
yields an empty (zero-dimensional) array instead of null. (This
does not match non-slice behavior and is done for historical reasons.)
If the requested slice partially overlaps the array bounds, then it
is silently reduced to just the overlapping region instead of
returning null.
</p><p>
The current dimensions of any array value can be retrieved with the
<code class="function">array_dims</code> function:
</p><pre class="programlisting">
SELECT array_dims(schedule) FROM sal_emp WHERE name = 'Carol';
array_dims
------------
[1:2][1:2]
(1 row)
</pre><p>
<code class="function">array_dims</code> produces a <code class="type">text</code> result,
which is convenient for people to read but perhaps inconvenient
for programs. Dimensions can also be retrieved with
<code class="function">array_upper</code> and <code class="function">array_lower</code>,
which return the upper and lower bound of a
specified array dimension, respectively:
</p><pre class="programlisting">
SELECT array_upper(schedule, 1) FROM sal_emp WHERE name = 'Carol';
array_upper
-------------
2
(1 row)
</pre><p>
<code class="function">array_length</code> will return the length of a specified
array dimension:
</p><pre class="programlisting">
SELECT array_length(schedule, 1) FROM sal_emp WHERE name = 'Carol';
array_length
--------------
2
(1 row)
</pre><p>
<code class="function">cardinality</code> returns the total number of elements in an
array across all dimensions. It is effectively the number of rows a call to
<code class="function">unnest</code> would yield:
</p><pre class="programlisting">
SELECT cardinality(schedule) FROM sal_emp WHERE name = 'Carol';
cardinality
-------------
4
(1 row)
</pre><p>
</p></div><div class="sect2" id="ARRAYS-MODIFYING"><div class="titlepage"><div><div><h3 class="title">8.15.4. Modifying Arrays</h3></div></div></div><a id="id-1.5.7.23.7.2" class="indexterm"></a><p>
An array value can be replaced completely:
</p><pre class="programlisting">
UPDATE sal_emp SET pay_by_quarter = '{25000,25000,27000,27000}'
WHERE name = 'Carol';
</pre><p>
or using the <code class="literal">ARRAY</code> expression syntax:
</p><pre class="programlisting">
UPDATE sal_emp SET pay_by_quarter = ARRAY[25000,25000,27000,27000]
WHERE name = 'Carol';
</pre><p>
An array can also be updated at a single element:
</p><pre class="programlisting">
UPDATE sal_emp SET pay_by_quarter[4] = 15000
WHERE name = 'Bill';
</pre><p>
or updated in a slice:
</p><pre class="programlisting">
UPDATE sal_emp SET pay_by_quarter[1:2] = '{27000,27000}'
WHERE name = 'Carol';
</pre><p>
The slice syntaxes with omitted <em class="replaceable"><code>lower-bound</code></em> and/or
<em class="replaceable"><code>upper-bound</code></em> can be used too, but only when
updating an array value that is not NULL or zero-dimensional (otherwise,
there is no existing subscript limit to substitute).
</p><p>
A stored array value can be enlarged by assigning to elements not already
present. Any positions between those previously present and the newly
assigned elements will be filled with nulls. For example, if array
<code class="literal">myarray</code> currently has 4 elements, it will have six
elements after an update that assigns to <code class="literal">myarray[6]</code>;
<code class="literal">myarray[5]</code> will contain null.
Currently, enlargement in this fashion is only allowed for one-dimensional
arrays, not multidimensional arrays.
</p><p>
Subscripted assignment allows creation of arrays that do not use one-based
subscripts. For example one might assign to <code class="literal">myarray[-2:7]</code> to
create an array with subscript values from -2 to 7.
</p><p>
New array values can also be constructed using the concatenation operator,
<code class="literal">||</code>:
</p><pre class="programlisting">
SELECT ARRAY[1,2] || ARRAY[3,4];
?column?
-----------
{1,2,3,4}
(1 row)
SELECT ARRAY[5,6] || ARRAY[[1,2],[3,4]];
?column?
---------------------
{{5,6},{1,2},{3,4}}
(1 row)
</pre><p>
</p><p>
The concatenation operator allows a single element to be pushed onto the
beginning or end of a one-dimensional array. It also accepts two
<em class="replaceable"><code>N</code></em>-dimensional arrays, or an <em class="replaceable"><code>N</code></em>-dimensional
and an <em class="replaceable"><code>N+1</code></em>-dimensional array.
</p><p>
When a single element is pushed onto either the beginning or end of a
one-dimensional array, the result is an array with the same lower bound
subscript as the array operand. For example:
</p><pre class="programlisting">
SELECT array_dims(1 || '[0:1]={2,3}'::int[]);
array_dims
------------
[0:2]
(1 row)
SELECT array_dims(ARRAY[1,2] || 3);
array_dims
------------
[1:3]
(1 row)
</pre><p>
</p><p>
When two arrays with an equal number of dimensions are concatenated, the
result retains the lower bound subscript of the left-hand operand's outer
dimension. The result is an array comprising every element of the left-hand
operand followed by every element of the right-hand operand. For example:
</p><pre class="programlisting">
SELECT array_dims(ARRAY[1,2] || ARRAY[3,4,5]);
array_dims
------------
[1:5]
(1 row)
SELECT array_dims(ARRAY[[1,2],[3,4]] || ARRAY[[5,6],[7,8],[9,0]]);
array_dims
------------
[1:5][1:2]
(1 row)
</pre><p>
</p><p>
When an <em class="replaceable"><code>N</code></em>-dimensional array is pushed onto the beginning
or end of an <em class="replaceable"><code>N+1</code></em>-dimensional array, the result is
analogous to the element-array case above. Each <em class="replaceable"><code>N</code></em>-dimensional
sub-array is essentially an element of the <em class="replaceable"><code>N+1</code></em>-dimensional
array's outer dimension. For example:
</p><pre class="programlisting">
SELECT array_dims(ARRAY[1,2] || ARRAY[[3,4],[5,6]]);
array_dims
------------
[1:3][1:2]
(1 row)
</pre><p>
</p><p>
An array can also be constructed by using the functions
<code class="function">array_prepend</code>, <code class="function">array_append</code>,
or <code class="function">array_cat</code>. The first two only support one-dimensional
arrays, but <code class="function">array_cat</code> supports multidimensional arrays.
Some examples:
</p><pre class="programlisting">
SELECT array_prepend(1, ARRAY[2,3]);
array_prepend
---------------
{1,2,3}
(1 row)
SELECT array_append(ARRAY[1,2], 3);
array_append
--------------
{1,2,3}
(1 row)
SELECT array_cat(ARRAY[1,2], ARRAY[3,4]);
array_cat
-----------
{1,2,3,4}
(1 row)
SELECT array_cat(ARRAY[[1,2],[3,4]], ARRAY[5,6]);
array_cat
---------------------
{{1,2},{3,4},{5,6}}
(1 row)
SELECT array_cat(ARRAY[5,6], ARRAY[[1,2],[3,4]]);
array_cat
---------------------
{{5,6},{1,2},{3,4}}
</pre><p>
</p><p>
In simple cases, the concatenation operator discussed above is preferred
over direct use of these functions. However, because the concatenation
operator is overloaded to serve all three cases, there are situations where
use of one of the functions is helpful to avoid ambiguity. For example
consider:
</p><pre class="programlisting">
SELECT ARRAY[1, 2] || '{3, 4}'; -- the untyped literal is taken as an array
?column?
-----------
{1,2,3,4}
SELECT ARRAY[1, 2] || '7'; -- so is this one
ERROR: malformed array literal: "7"
SELECT ARRAY[1, 2] || NULL; -- so is an undecorated NULL
?column?
----------
{1,2}
(1 row)
SELECT array_append(ARRAY[1, 2], NULL); -- this might have been meant
array_append
--------------
{1,2,NULL}
</pre><p>
In the examples above, the parser sees an integer array on one side of the
concatenation operator, and a constant of undetermined type on the other.
The heuristic it uses to resolve the constant's type is to assume it's of
the same type as the operator's other input — in this case,
integer array. So the concatenation operator is presumed to
represent <code class="function">array_cat</code>, not <code class="function">array_append</code>. When
that's the wrong choice, it could be fixed by casting the constant to the
array's element type; but explicit use of <code class="function">array_append</code> might
be a preferable solution.
</p></div><div class="sect2" id="ARRAYS-SEARCHING"><div class="titlepage"><div><div><h3 class="title">8.15.5. Searching in Arrays</h3></div></div></div><a id="id-1.5.7.23.8.2" class="indexterm"></a><p>
To search for a value in an array, each value must be checked.
This can be done manually, if you know the size of the array.
For example:
</p><pre class="programlisting">
SELECT * FROM sal_emp WHERE pay_by_quarter[1] = 10000 OR
pay_by_quarter[2] = 10000 OR
pay_by_quarter[3] = 10000 OR
pay_by_quarter[4] = 10000;
</pre><p>
However, this quickly becomes tedious for large arrays, and is not
helpful if the size of the array is unknown. An alternative method is
described in <a class="xref" href="functions-comparisons.html" title="9.23. Row and Array Comparisons">Section 9.23</a>. The above
query could be replaced by:
</p><pre class="programlisting">
SELECT * FROM sal_emp WHERE 10000 = ANY (pay_by_quarter);
</pre><p>
In addition, you can find rows where the array has all values
equal to 10000 with:
</p><pre class="programlisting">
SELECT * FROM sal_emp WHERE 10000 = ALL (pay_by_quarter);
</pre><p>
</p><p>
Alternatively, the <code class="function">generate_subscripts</code> function can be used.
For example:
</p><pre class="programlisting">
SELECT * FROM
(SELECT pay_by_quarter,
generate_subscripts(pay_by_quarter, 1) AS s
FROM sal_emp) AS foo
WHERE pay_by_quarter[s] = 10000;
</pre><p>
This function is described in <a class="xref" href="functions-srf.html#FUNCTIONS-SRF-SUBSCRIPTS" title="Table 9.59. Subscript Generating Functions">Table 9.59</a>.
</p><p>
You can also search an array using the <code class="literal">&&</code> operator,
which checks whether the left operand overlaps with the right operand.
For instance:
</p><pre class="programlisting">
SELECT * FROM sal_emp WHERE pay_by_quarter && ARRAY[10000];
</pre><p>
This and other array operators are further described in
<a class="xref" href="functions-array.html" title="9.18. Array Functions and Operators">Section 9.18</a>. It can be accelerated by an appropriate
index, as described in <a class="xref" href="indexes-types.html" title="11.2. Index Types">Section 11.2</a>.
</p><p>
You can also search for specific values in an array using the <code class="function">array_position</code>
and <code class="function">array_positions</code> functions. The former returns the subscript of
the first occurrence of a value in an array; the latter returns an array with the
subscripts of all occurrences of the value in the array. For example:
</p><pre class="programlisting">
SELECT array_position(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon');
array_positions
-----------------
2
SELECT array_positions(ARRAY[1, 4, 3, 1, 3, 4, 2, 1], 1);
array_positions
-----------------
{1,4,8}
</pre><p>
</p><div class="tip"><h3 class="title">Tip</h3><p>
Arrays are not sets; searching for specific array elements
can be a sign of database misdesign. Consider
using a separate table with a row for each item that would be an
array element. This will be easier to search, and is likely to
scale better for a large number of elements.
</p></div></div><div class="sect2" id="ARRAYS-IO"><div class="titlepage"><div><div><h3 class="title">8.15.6. Array Input and Output Syntax</h3></div></div></div><a id="id-1.5.7.23.9.2" class="indexterm"></a><p>
The external text representation of an array value consists of items that
are interpreted according to the I/O conversion rules for the array's
element type, plus decoration that indicates the array structure.
The decoration consists of curly braces (<code class="literal">{</code> and <code class="literal">}</code>)
around the array value plus delimiter characters between adjacent items.
The delimiter character is usually a comma (<code class="literal">,</code>) but can be
something else: it is determined by the <code class="literal">typdelim</code> setting
for the array's element type. Among the standard data types provided
in the <span class="productname">PostgreSQL</span> distribution, all use a comma,
except for type <code class="type">box</code>, which uses a semicolon (<code class="literal">;</code>).
In a multidimensional array, each dimension (row, plane,
cube, etc.) gets its own level of curly braces, and delimiters
must be written between adjacent curly-braced entities of the same level.
</p><p>
The array output routine will put double quotes around element values
if they are empty strings, contain curly braces, delimiter characters,
double quotes, backslashes, or white space, or match the word
<code class="literal">NULL</code>. Double quotes and backslashes
embedded in element values will be backslash-escaped. For numeric
data types it is safe to assume that double quotes will never appear, but
for textual data types one should be prepared to cope with either the presence
or absence of quotes.
</p><p>
By default, the lower bound index value of an array's dimensions is
set to one. To represent arrays with other lower bounds, the array
subscript ranges can be specified explicitly before writing the
array contents.
This decoration consists of square brackets (<code class="literal">[]</code>)
around each array dimension's lower and upper bounds, with
a colon (<code class="literal">:</code>) delimiter character in between. The
array dimension decoration is followed by an equal sign (<code class="literal">=</code>).
For example:
</p><pre class="programlisting">
SELECT f1[1][-2][3] AS e1, f1[1][-1][5] AS e2
FROM (SELECT '[1:1][-2:-1][3:5]={{{1,2,3},{4,5,6}}}'::int[] AS f1) AS ss;
e1 | e2
----+----
1 | 6
(1 row)
</pre><p>
The array output routine will include explicit dimensions in its result
only when there are one or more lower bounds different from one.
</p><p>
If the value written for an element is <code class="literal">NULL</code> (in any case
variant), the element is taken to be NULL. The presence of any quotes
or backslashes disables this and allows the literal string value
<span class="quote">“<span class="quote">NULL</span>”</span> to be entered. Also, for backward compatibility with
pre-8.2 versions of <span class="productname">PostgreSQL</span>, the <a class="xref" href="runtime-config-compatible.html#GUC-ARRAY-NULLS">array_nulls</a> configuration parameter can be turned
<code class="literal">off</code> to suppress recognition of <code class="literal">NULL</code> as a NULL.
</p><p>
As shown previously, when writing an array value you can use double
quotes around any individual array element. You <span class="emphasis"><em>must</em></span> do so
if the element value would otherwise confuse the array-value parser.
For example, elements containing curly braces, commas (or the data type's
delimiter character), double quotes, backslashes, or leading or trailing
whitespace must be double-quoted. Empty strings and strings matching the
word <code class="literal">NULL</code> must be quoted, too. To put a double
quote or backslash in a quoted array element value, precede it
with a backslash. Alternatively, you can avoid quotes and use
backslash-escaping to protect all data characters that would otherwise
be taken as array syntax.
</p><p>
You can add whitespace before a left brace or after a right
brace. You can also add whitespace before or after any individual item
string. In all of these cases the whitespace will be ignored. However,
whitespace within double-quoted elements, or surrounded on both sides by
non-whitespace characters of an element, is not ignored.
</p><div class="tip"><h3 class="title">Tip</h3><p>
The <code class="literal">ARRAY</code> constructor syntax (see
<a class="xref" href="sql-expressions.html#SQL-SYNTAX-ARRAY-CONSTRUCTORS" title="4.2.12. Array Constructors">Section 4.2.12</a>) is often easier to work
with than the array-literal syntax when writing array values in SQL
commands. In <code class="literal">ARRAY</code>, individual element values are written the
same way they would be written when not members of an array.
</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="datatype-json.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="datatype.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="rowtypes.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">8.14. <acronym class="acronym">JSON</acronym> Types </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 8.16. Composite Types</td></tr></table></div></body></html>
