-<!-- $PostgreSQL: pgsql/doc/src/sgml/array.sgml,v 1.46 2005/11/04 23:13:59 petere Exp $ -->
+<!-- doc/src/sgml/array.sgml -->
<sect1 id="arrays">
<title>Arrays</title>
<para>
<productname>PostgreSQL</productname> 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.)
+ built-in or user-defined base type, enum type, or composite type
+ can be created.
+ Arrays of domains are not yet supported.
</para>
- <sect2>
+ <sect2 id="arrays-declaration">
<title>Declaration of Array Types</title>
+ <indexterm>
+ <primary>array</primary>
+ <secondary>declaration</secondary>
+ </indexterm>
+
<para>
To illustrate the use of array types, we create this table:
<programlisting>
);
</programlisting>
- However, the current implementation does not enforce the array size
- limits — the behavior is the same as for arrays of unspecified
+ However, the current implementation ignores any supplied array size
+ limits, i.e., the behavior is the same as for arrays of unspecified
length.
</para>
<para>
- Actually, the current implementation does not enforce the declared
+ 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
- <command>CREATE TABLE</command> is simply documentation, it does not
+ of dimensions. So, declaring the array size or number of dimensions in
+ <command>CREATE TABLE</command> is simply documentation; it does not
affect run-time behavior.
</para>
<para>
- An alternative syntax, which conforms to the SQL standard, may
- be used for one-dimensional arrays.
+ An alternative syntax, which conforms to the SQL standard by using
+ the keyword <literal>ARRAY</>, can be used for one-dimensional arrays.
<structfield>pay_by_quarter</structfield> could have been defined
as:
<programlisting>
pay_by_quarter integer ARRAY[4],
</programlisting>
- This syntax requires an integer constant to denote the array size.
+ Or, if no array size is to be specified:
+<programlisting>
+ pay_by_quarter integer ARRAY,
+</programlisting>
As before, however, <productname>PostgreSQL</> does not enforce the
- size restriction.
+ size restriction in any case.
</para>
</sect2>
- <sect2>
+ <sect2 id="arrays-input">
<title>Array Value Input</title>
<indexterm>
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,
+ 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:
where <replaceable>delim</replaceable> is the delimiter character
for the type, as recorded in its <literal>pg_type</literal> entry.
Among the standard data types provided in the
- <productname>PostgreSQL</productname> distribution, type
- <literal>box</> uses a semicolon (<literal>;</>) but all the others
- use comma (<literal>,</>). Each <replaceable>val</replaceable> is
+ <productname>PostgreSQL</productname> distribution, all use a comma
+ (<literal>,</>), except for type <type>box</> which uses a semicolon
+ (<literal>;</>). Each <replaceable>val</replaceable> is
either a constant of the array element type, or a subarray. An example
- of an array constant is
+ of an array constant is:
<programlisting>
'{{1,2,3},{4,5,6},{7,8,9}}'
</programlisting>
three subarrays of integers.
</para>
+ <para>
+ To set an element of an array constant to NULL, write <literal>NULL</>
+ for the element value. (Any upper- or lower-case variant of
+ <literal>NULL</> will do.) If you want an actual string value
+ <quote>NULL</>, you must put double quotes around it.
+ </para>
+
<para>
(These kinds of array constants are actually only a special case of
the generic type constants discussed in <xref
</para>
<para>
- Now we can show some <command>INSERT</command> statements.
-
-<programlisting>
-INSERT INTO sal_emp
- VALUES ('Bill',
- '{10000, 10000, 10000, 10000}',
- '{{"meeting", "lunch"}, {"meeting"}}');
-ERROR: multidimensional arrays must have array expressions with matching dimensions
-</programlisting>
-
- Note that multidimensional arrays must have matching extents for each
- dimension. A mismatch causes an error report.
+ Now we can show some <command>INSERT</command> statements:
<programlisting>
INSERT INTO sal_emp
</programlisting>
</para>
- <para>
- 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.)
- </para>
-
<para>
The result of the previous two inserts looks like this:
+
<programlisting>
SELECT * FROM sal_emp;
name | pay_by_quarter | schedule
</para>
<para>
- The <literal>ARRAY</> constructor syntax may also be used:
+ Multidimensional arrays must have matching extents for each
+ dimension. A mismatch causes an error, for example:
+
+<programlisting>
+INSERT INTO sal_emp
+ VALUES ('Bill',
+ '{10000, 10000, 10000, 10000}',
+ '{{"meeting", "lunch"}, {"meeting"}}');
+ERROR: multidimensional arrays must have array expressions with matching dimensions
+</programlisting>
+ </para>
+
+ <para>
+ The <literal>ARRAY</> constructor syntax can also be used:
<programlisting>
INSERT INTO sal_emp
VALUES ('Bill',
</para>
</sect2>
- <sect2>
+ <sect2 id="arrays-accessing">
<title>Accessing Arrays</title>
+ <indexterm>
+ <primary>array</primary>
+ <secondary>accessing</secondary>
+ </indexterm>
+
<para>
Now, we can run some queries on the table.
- First, we show how to access a single element of an array at a time.
+ 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:
-
+
<programlisting>
SELECT name FROM sal_emp WHERE pay_by_quarter[1] <> pay_by_quarter[2];
</programlisting>
The array subscript numbers are written within square brackets.
- By default <productname>PostgreSQL</productname> uses the
+ By default <productname>PostgreSQL</productname> uses a
one-based numbering convention for arrays, that is,
an array of <replaceable>n</> elements starts with <literal>array[1]</literal> and
ends with <literal>array[<replaceable>n</>]</literal>.
<para>
This query retrieves the third quarter pay of all employees:
-
+
<programlisting>
SELECT pay_by_quarter[3] FROM sal_emp;
<literal><replaceable>lower-bound</replaceable>:<replaceable>upper-bound</replaceable></literal>
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:
-
+
<programlisting>
SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';
(1 row)
</programlisting>
- We could also have written
+ 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, <literal>[2]</> is treated as
+ <literal>[1:2]</>, as in this example:
<programlisting>
-SELECT schedule[1:2][1] FROM sal_emp WHERE name = 'Bill';
-</programlisting>
-
- 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
- <literal><replaceable>lower</replaceable>:<replaceable>upper</replaceable></literal>.
- A lower bound of 1 is assumed for any subscript where only one value
- is specified, as in this example:
-<programlisting>
SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill';
schedule
-------------------------------------------
{{meeting,lunch},{training,presentation}}
(1 row)
+</programlisting>
+
+ To avoid confusion with the non-slice case, it's best to use slice syntax
+ for all dimensions, e.g., <literal>[1:2][1:1]</>, not <literal>[2][1:1]</>.
+ </para>
+
+ <para>
+ It is possible to omit the <replaceable>lower-bound</replaceable> and/or
+ <replaceable>upper-bound</replaceable> of a slice specifier; the missing
+ bound is replaced by the lower or upper limit of the array's subscripts.
+ For example:
+
+<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)
</programlisting>
</para>
<para>
- Fetching from outside the current bounds of an array yields a
- SQL null value, not an error. For example, if <literal>schedule</>
+ 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 <literal>schedule</>
currently has the dimensions <literal>[1:3][1:2]</> then referencing
<literal>schedule[3][3]</> 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.
+ </para>
+
+ <para>
+ 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.
</para>
<para>
array_dims
------------
- [1:2][1:1]
+ [1:2][1:2]
(1 row)
</programlisting>
<function>array_dims</function> produces a <type>text</type> result,
- which is convenient for people to read but perhaps not so convenient
+ which is convenient for people to read but perhaps inconvenient
for programs. Dimensions can also be retrieved with
<function>array_upper</function> and <function>array_lower</function>,
which return the upper and lower bound of a
- specified array dimension, respectively.
+ specified array dimension, respectively:
<programlisting>
SELECT array_upper(schedule, 1) FROM sal_emp WHERE name = 'Carol';
-------------
2
(1 row)
+</programlisting>
+
+ <function>array_length</function> will return the length of a specified
+ array dimension:
+
+<programlisting>
+SELECT array_length(schedule, 1) FROM sal_emp WHERE name = 'Carol';
+
+ array_length
+--------------
+ 2
+(1 row)
+</programlisting>
+
+ <function>cardinality</function> returns the total number of elements in an
+ array across all dimensions. It is effectively the number of rows a call to
+ <function>unnest</function> would yield:
+
+<programlisting>
+SELECT cardinality(schedule) FROM sal_emp WHERE name = 'Carol';
+
+ cardinality
+-------------
+ 4
+(1 row)
</programlisting>
</para>
</sect2>
- <sect2>
+ <sect2 id="arrays-modifying">
<title>Modifying Arrays</title>
+ <indexterm>
+ <primary>array</primary>
+ <secondary>modifying</secondary>
+ </indexterm>
+
<para>
An array value can be replaced completely:
WHERE name = 'Carol';
</programlisting>
- An array may also be updated at a single element:
+ An array can also be updated at a single element:
<programlisting>
UPDATE sal_emp SET pay_by_quarter[4] = 15000
WHERE name = 'Bill';
-</programListing>
+</programlisting>
or updated in a slice:
WHERE name = 'Carol';
</programlisting>
+ The slice syntaxes with omitted <replaceable>lower-bound</replaceable> and/or
+ <replaceable>upper-bound</replaceable> 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).
</para>
<para>
- 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
- <literal>myarray</> currently has 4 elements, it will have five
- elements after an update that assigns to <literal>myarray[5]</>.
+ 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
+ <literal>myarray</> currently has 4 elements, it will have six
+ elements after an update that assigns to <literal>myarray[6]</>;
+ <literal>myarray[5]</> will contain null.
Currently, enlargement in this fashion is only allowed for one-dimensional
arrays, not multidimensional arrays.
</para>
<para>
- Array slice assignment allows creation of arrays that do not use one-based
+ Subscripted assignment allows creation of arrays that do not use one-based
subscripts. For example one might assign to <literal>myarray[-2:7]</> to
- create an array with subscript values running from -2 to 7.
+ create an array with subscript values from -2 to 7.
</para>
<para>
- New array values can also be constructed by using the concatenation operator,
- <literal>||</literal>.
+ New array values can also be constructed using the concatenation operator,
+ <literal>||</literal>:
<programlisting>
SELECT ARRAY[1,2] || ARRAY[3,4];
?column?
</para>
<para>
- The concatenation operator allows a single element to be pushed on to the
+ The concatenation operator allows a single element to be pushed onto the
beginning or end of a one-dimensional array. It also accepts two
<replaceable>N</>-dimensional arrays, or an <replaceable>N</>-dimensional
and an <replaceable>N+1</>-dimensional array.
</para>
<para>
- 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:
+ 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:
<programlisting>
-SELECT array_dims(1 || ARRAY[2,3]);
+SELECT array_dims(1 || '[0:1]={2,3}'::int[]);
array_dims
------------
[0:2]
</para>
<para>
- When an <replaceable>N</>-dimensional array is pushed on to the beginning
+ When an <replaceable>N</>-dimensional array is pushed onto the beginning
or end of an <replaceable>N+1</>-dimensional array, the result is
analogous to the element-array case above. Each <replaceable>N</>-dimensional
sub-array is essentially an element of the <replaceable>N+1</>-dimensional
SELECT array_dims(ARRAY[1,2] || ARRAY[[3,4],[5,6]]);
array_dims
------------
- [0:2][1:2]
+ [1:3][1:2]
(1 row)
</programlisting>
</para>
<function>array_prepend</function>, <function>array_append</function>,
or <function>array_cat</function>. The first two only support one-dimensional
arrays, but <function>array_cat</function> 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:
+ Some examples:
<programlisting>
SELECT array_prepend(1, ARRAY[2,3]);
{{5,6},{1,2},{3,4}}
</programlisting>
</para>
+
+ <para>
+ 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:
+
+<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}
+</programlisting>
+
+ 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 <function>array_cat</>, not <function>array_append</>. When
+ that's the wrong choice, it could be fixed by casting the constant to the
+ array's element type; but explicit use of <function>array_append</> might
+ be a preferable solution.
+ </para>
</sect2>
- <sect2>
+ <sect2 id="arrays-searching">
<title>Searching in Arrays</title>
+ <indexterm>
+ <primary>array</primary>
+ <secondary>searching</secondary>
+ </indexterm>
+
<para>
- 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.
+ 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:
<programlisting>
</programlisting>
However, this quickly becomes tedious for large arrays, and is not
- helpful if the size of the array is uncertain. An alternative method is
+ helpful if the size of the array is unknown. An alternative method is
described in <xref linkend="functions-comparisons">. The above
query could be replaced by:
SELECT * FROM sal_emp WHERE 10000 = ANY (pay_by_quarter);
</programlisting>
- In addition, you could find rows where the array had all values
+ In addition, you can find rows where the array has all values
equal to 10000 with:
<programlisting>
</para>
+ <para>
+ Alternatively, the <function>generate_subscripts</> function can be used.
+ For example:
+
+<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;
+</programlisting>
+
+ This function is described in <xref linkend="functions-srf-subscripts">.
+ </para>
+
+ <para>
+ You can also search an array using the <literal>&&</> operator,
+ which checks whether the left operand overlaps with the right operand.
+ For instance:
+
+<programlisting>
+SELECT * FROM sal_emp WHERE pay_by_quarter && ARRAY[10000];
+</programlisting>
+
+ This and other array operators are further described in
+ <xref linkend="functions-array">. It can be accelerated by an appropriate
+ index, as described in <xref linkend="indexes-types">.
+ </para>
+
+ <para>
+ You can also search for specific values in an array using the <function>array_position</>
+ and <function>array_positions</> 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:
+
+<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}
+</programlisting>
+ </para>
+
<tip>
<para>
Arrays are not sets; searching for specific array elements
- may be a sign of database misdesign. Consider
+ 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 up better to large numbers of elements.
+ scale better for a large number of elements.
</para>
</tip>
</sect2>
- <sect2>
+ <sect2 id="arrays-io">
<title>Array Input and Output Syntax</title>
+ <indexterm>
+ <primary>array</primary>
+ <secondary>I/O</secondary>
+ </indexterm>
+
<para>
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
around the array value plus delimiter characters between adjacent items.
The delimiter character is usually a comma (<literal>,</>) but can be
something else: it is determined by the <literal>typdelim</> setting
- for the array's element type. (Among the standard data types provided
- in the <productname>PostgreSQL</productname> distribution, type
- <literal>box</> uses a semicolon (<literal>;</>) but all the others
- use comma.) In a multidimensional array, each dimension (row, plane,
+ for the array's element type. Among the standard data types provided
+ in the <productname>PostgreSQL</productname> distribution, all use a comma,
+ except for type <type>box</>, which uses a semicolon (<literal>;</>).
+ 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.
</para>
<para>
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
+ if they are empty strings, contain curly braces, delimiter characters,
+ double quotes, backslashes, or white space, or match the word
+ <literal>NULL</>. 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
- <productname>PostgreSQL</productname> releases.)
+ for textual data types one should be prepared to cope with either the presence
+ or absence of quotes.
</para>
<para>
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.
+ 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 (<literal>[]</>)
around each array dimension's lower and upper bounds, with
a colon (<literal>:</>) delimiter character in between. The
array dimension decoration is followed by an equal sign (<literal>=</>).
For example:
<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)
-</programlisting>
- </para>
-
- <para>
- This syntax can also be used to specify non-default array subscripts
- in an array literal. For example:
-<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;
1 | 6
(1 row)
</programlisting>
+ The array output routine will include explicit dimensions in its result
+ only when there are one or more lower bounds different from one.
+ </para>
+
+ <para>
+ If the value written for an element is <literal>NULL</> (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
+ <quote>NULL</> to be entered. Also, for backward compatibility with
+ pre-8.2 versions of <productname>PostgreSQL</>, the <xref
+ linkend="guc-array-nulls"> configuration parameter can be turned
+ <literal>off</> to suppress recognition of <literal>NULL</> as a NULL.
</para>
<para>
- As shown previously, when writing an array value you may write double
+ As shown previously, when writing an array value you can use double
quotes around any individual array element. You <emphasis>must</> 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.
+ 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 <literal>NULL</> must be quoted, too. To put a double quote or
+ backslash in a quoted array element value, use escape string syntax
+ and 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.
</para>
<para>
- You may write whitespace before a left brace or after a right
- brace. You may also write whitespace before or after any individual item
+ 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.
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 <type>text</> array
- value containing a backslash and a double quote, you'd need to write
+ value containing a backslash and a double quote, you'd need to write:
<programlisting>
-INSERT ... VALUES ('{"\\\\","\\""}');
+INSERT ... VALUES (E'{"\\\\","\\""}');
</programlisting>
- The string-literal processor removes one level of backslashes, so that
+ The escape string processor removes one level of backslashes, so that
what arrives at the array-value parser looks like <literal>{"\\","\""}</>.
In turn, the strings fed to the <type>text</> data type's input routine
become <literal>\</> and <literal>"</> respectively. (If we were working
with a data type whose input routine also treated backslashes specially,
<type>bytea</> 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 <xref linkend="sql-syntax-dollar-quoting">) may be
+ Dollar quoting (see <xref linkend="sql-syntax-dollar-quoting">) can be
used to avoid the need to double backslashes.
</para>
</note>
projects / postgresql / blobdiff