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<title>8.10.Arrays</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="arrays"></a>8.10.Arrays</h2></div></div></div>
<a name="id591273"></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 can be created.  (Arrays of
  composite types or domains are not yet supported, however.)
 </p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id591292"></a>8.10.1.Declaration of Array Types</h3></div></div></div>
<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 does not enforce the array size
  limits [mdash ] the behavior is the same as for arrays of unspecified
  length.
 </p>
<p>  Actually, 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 number of dimensions or sizes 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, may
  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>
  This syntax requires an integer constant to denote the array size.
  As before, however, <span class="productname">PostgreSQL</span> does not enforce the
  size restriction.
 </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id591410"></a>8.10.2.Array Value Input</h3></div></div></div>
<a name="id591414"></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 may 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, type
   <code class="literal">box</code> uses a semicolon (<code class="literal">;</code>) but all the others
   use comma (<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>   (These kinds of array constants are actually only a special case of
   the generic type constants discussed in <a href="sql-syntax.html#sql-syntax-constants-generic" title="4.1.2.5.Constants of Other Types">Section4.1.2.5, &#8220;Constants of Other Types&#8221;</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"}, {"meeting"}}');
ERROR:  multidimensional arrays must have array expressions with matching dimensions</pre>
<p>

  Note that multidimensional arrays must have matching extents for each
  dimension. A mismatch causes an error report.

</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>   A limitation of the present array implementation is that individual
   elements of an array cannot be SQL null values.  The entire array
   can be set to null, but you can't have an array with some elements
   null and some not.  (This is likely to change in the future.)
  </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>  The <code class="literal">ARRAY</code> constructor syntax may 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 href="sql-expressions.html#sql-syntax-array-constructors" title="4.2.10.Array Constructors">Section4.2.10, &#8220;Array Constructors&#8221;</a>.
 </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id591619"></a>8.10.3.Accessing Arrays</h3></div></div></div>
<p>  Now, we can run some queries on the table.
  First, we show how to access a single element of an array at a time.
  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] &lt;&gt; 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 the
  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>

  We could also have written

</p>
<pre class="programlisting">SELECT schedule[1:2][1] FROM sal_emp WHERE name = 'Bill';</pre>
<p>

  with the same result.  An array subscripting operation is always taken to
  represent an array slice if any of the subscripts are written in the form
  <code class="literal"><em class="replaceable"><code>lower</code></em>:<em class="replaceable"><code>upper</code></em></code>.
  A lower bound of 1 is assumed for any subscript where only one value
  is specified, 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>
 </p>
<p>  Fetching from outside the current bounds of an array yields a
  SQL null value, not 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.
  Fetching an array slice that
  is completely outside the current bounds likewise yields a null array;
  but if the requested slice partially overlaps the array bounds, then it
  is silently reduced to just the overlapping region.
 </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][1:1]
(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 not so convenient
  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>
 </p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id591827"></a>8.10.4.Modifying Arrays</h3></div></div></div>
<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 may 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>

 </p>
<p>  A stored array value can be enlarged by assigning to an element adjacent to
  those already present, or by assigning to a slice that is adjacent
  to or overlaps the data already present.  For example, if array
  <code class="literal">myarray</code> currently has 4 elements, it will have five
  elements after an update that assigns to <code class="literal">myarray[5]</code>.
  Currently, enlargement in this fashion is only allowed for one-dimensional
  arrays, not multidimensional arrays.
 </p>
<p>  Array slice 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 running from -2 to 7.
 </p>
<p>  New array values can also be constructed by 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 on to 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 on to the beginning of a one-dimensional
  array, the result is an array with a lower bound subscript equal to
  the right-hand operand's lower bound subscript, minus one. When a single
  element is pushed on to the end of a one-dimensional array, the result is
  an array retaining the lower bound of the left-hand operand. For example:
</p>
<pre class="programlisting">SELECT array_dims(1 || ARRAY[2,3]);
 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 on to 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
------------
 [0:2][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.

  Note that the concatenation operator discussed above is preferred over
  direct use of these functions. In fact, the functions are primarily for use
  in implementing the concatenation operator. However, they may be directly
  useful in the creation of user-defined aggregates. 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>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id592063"></a>8.10.5.Searching in Arrays</h3></div></div></div>
<p>  To search for a value in an array, you must check each value of the
  array. This can be done by hand, 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 uncertain. An alternative method is
  described in <a href="functions-comparisons.html" title="9.17.Row and Array Comparisons">Section9.17, &#8220;Row and Array Comparisons&#8221;</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 could find rows where the array had all values
  equal to 10000 with:

</p>
<pre class="programlisting">SELECT * FROM sal_emp WHERE 10000 = ALL (pay_by_quarter);</pre>
<p>

 </p>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Tip</h3>
<p>   Arrays are not sets; searching for specific array elements
   may 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 up better to large numbers of elements.
  </p>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id592118"></a>8.10.6.Array Input and Output Syntax</h3></div></div></div>
<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, type
   <code class="literal">box</code> uses a semicolon (<code class="literal">;</code>) but all the others
   use comma.)  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 or contain curly braces, delimiter characters,
   double quotes, backslashes, or white space.  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 presence
   or absence of quotes.  (This is a change in behavior from pre-7.2
   <span class="productname">PostgreSQL</span> releases.)
  </p>
<p>   By default, the lower bound index value of an array's dimensions is
   set to one. If any of an array's dimensions has a lower bound index not
   equal to one, an additional decoration that indicates the actual
   array dimensions will precede the array structure decoration.
   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 1 || ARRAY[2,3] AS array;

     array
---------------
 [0:2]={1,2,3}
(1 row)

SELECT ARRAY[1,2] || ARRAY[[3,4]] AS array;

          array
--------------------------
 [0:1][1:2]={{1,2},{3,4}}
(1 row)</pre>
<p>
  </p>
<p>   This syntax can also be used to specify non-default array subscripts
   in an array literal. 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>
  </p>
<p>   As shown previously, when writing an array value you may write 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 whatever the
   delimiter character is), double quotes, backslashes, or leading or trailing
   whitespace must be double-quoted.  To put a double quote or backslash in a
   quoted array element value, precede it with a backslash. Alternatively, you
   can use backslash-escaping to protect all data characters that would
   otherwise be taken as array syntax.
  </p>
<p>   You may write whitespace before a left brace or after a right
   brace. You may also write 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="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>   Remember that what you write in an SQL command will first be interpreted
   as a string literal, and then as an array.  This doubles the number of
   backslashes you need.  For example, to insert a <code class="type">text</code> array
   value containing a backslash and a double quote, you'd need to write
</p>
<pre class="programlisting">INSERT ... VALUES ('{"\\\\","\\""}');</pre>
<p>
   The string-literal processor removes one level of backslashes, so that
   what arrives at the array-value parser looks like <code class="literal">{"\\","\""}</code>.
   In turn, the strings fed to the <code class="type">text</code> data type's input routine
   become <code class="literal">\</code> and <code class="literal">"</code> respectively.  (If we were working
   with a data type whose input routine also treated backslashes specially,
   <code class="type">bytea</code> for example, we might need as many as eight backslashes
   in the command to get one backslash into the stored array element.)
   Dollar quoting (see <a href="sql-syntax.html#sql-syntax-dollar-quoting" title="4.1.2.2.Dollar-Quoted String Constants">Section4.1.2.2, &#8220;Dollar-Quoted String Constants&#8221;</a>) may be
   used to avoid the need to double backslashes.
  </p>
</div>
<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Tip</h3>
<p>   The <code class="literal">ARRAY</code> constructor syntax (see
   <a href="sql-expressions.html#sql-syntax-array-constructors" title="4.2.10.Array Constructors">Section4.2.10, &#8220;Array Constructors&#8221;</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>
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