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Diffstat (limited to 'doc/src/sgml/array.sgml')
| -rw-r--r-- | doc/src/sgml/array.sgml | 42 |
1 files changed, 35 insertions, 7 deletions
diff --git a/doc/src/sgml/array.sgml b/doc/src/sgml/array.sgml index 5947df26c7a..427a3956cd3 100644 --- a/doc/src/sgml/array.sgml +++ b/doc/src/sgml/array.sgml @@ -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> |