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Document the array_dims() function, and make some other small improvements

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in the docs for arrays.
This commit is contained in:
Tom Lane
2000-12-18 23:39:37 +00:00
parent 1f159e562b
commit e4eb91048c
3 changed files with 45 additions and 18 deletions
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42
doc/src/sgml/array.sgml
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@@ -1,3 +1,7 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/array.sgml,v 1.8 2000/12/18 23:39:37 tgl Exp $
-->
<Chapter Id="arrays">
<Title>Arrays</Title>
@@ -30,7 +34,7 @@ CREATE TABLE sal_emp (
(pay_by_quarter), which represents the employee's
salary by quarter, and a two-dimensional array of <FirstTerm>text</FirstTerm>
(schedule), which represents the employee's weekly
schedule. Now we do some <FirstTerm>INSERTS</FirstTerm>s; note that when
schedule. Now we do some <FirstTerm>INSERT</FirstTerm>s; note that when
appending to an array, we enclose the values within
braces and separate them by commas. If you know <FirstTerm>C</FirstTerm>,
this is not unlike the syntax for initializing structures.
@@ -82,9 +86,10 @@ SELECT pay_by_quarter[3] FROM sal_emp;
</Para>
<Para>
We can also access arbitrary slices of an array, or
We can also access arbitrary rectangular slices of an array, or
subarrays. An array slice is denoted by writing
"lower subscript : upper subscript" for one or more array
<replaceable>lower subscript</replaceable> <literal>:</literal>
<replaceable>upper subscript</replaceable> for one or more array
dimensions. This query retrieves the first item on
Bill's schedule for the first two days of the week:
@@ -103,7 +108,11 @@ SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';
SELECT schedule[1:2][1] FROM sal_emp WHERE name = 'Bill';
</ProgramListing>
with the same result.
with the same result. An array subscripting operation is taken to
represent an array slice if any of the subscripts are written in
the form <replaceable>lower</replaceable> <literal>:</literal>
<replaceable>upper</replaceable>. A lower bound of 1 is assumed
for any subscript where only one value is specified.
</Para>
<Para>
@@ -114,7 +123,7 @@ UPDATE sal_emp SET pay_by_quarter = '{25000,25000,27000,27000}'
WHERE name = 'Carol';
</ProgramListing>
or updated at a single entry:
or updated at a single element:
<ProgramListing>
UPDATE sal_emp SET pay_by_quarter[4] = 15000
@@ -132,10 +141,11 @@ UPDATE sal_emp SET pay_by_quarter[1:2] = '{27000,27000}'
<Para>
An array 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. Currently, this is only
allowed for one-dimensional arrays, not multidimensional arrays.
to or overlaps the data already present.
For example, if an array value currently has 4 elements, it will
have five elements after an update that assigns to array[5].
Currently, enlargement in this fashion is only
allowed for one-dimensional arrays, not multidimensional arrays.
</Para>
<Para>
@@ -160,4 +170,22 @@ CREATE TABLE tictactoe (
number of dimensions.
</Para>
<Para>
The current dimensions of any array value can be retrieved with
the <function>array_dims</function> function:
<ProgramListing>
SELECT array_dims(schedule) FROM sal_emp WHERE name = 'Carol';
array_dims
------------
[1:2][1:1]
(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
for programs.
</Para>
</Chapter>