diff --git a/doc/src/sgml/array.sgml b/doc/src/sgml/array.sgml
index bbc0a07f56..aa7ecdc711 100644
--- a/doc/src/sgml/array.sgml
+++ b/doc/src/sgml/array.sgml
@@ -10,14 +10,13 @@ This must become a chapter on array behavior. Volunteers? - thomas 1998-01-12
- Postgres allows attributes of an instance to be defined
- as fixed-length or variable-length multi-dimensional
- arrays. Arrays of any base type or user-defined type
- can be created. To illustrate their use, we first create a
- class with arrays of base types.
+ Postgres allows attributes of a class
+ to be defined as variable-length multi-dimensional
+ arrays. Arrays of any built-in type or user-defined type
+ can be created. To illustrate their use, we create this class:
-CREATE TABLE SAL_EMP (
+CREATE TABLE sal_emp (
name text,
pay_by_quarter int4[],
schedule text[][]
@@ -26,10 +25,10 @@ CREATE TABLE SAL_EMP (
- The above query will create a class named SAL_EMP with
+ The above query will create a class named sal_emp with
a text string (name), a one-dimensional array of int4
(pay_by_quarter), which represents the employee's
- salary by quarter and a two-dimensional array of text
+ salary by quarter, and a two-dimensional array of text
(schedule), which represents the employee's weekly
schedule. Now we do some INSERTSs; note that when
appending to an array, we enclose the values within
@@ -37,20 +36,18 @@ CREATE TABLE SAL_EMP (
this is not unlike the syntax for initializing structures.
-INSERT INTO SAL_EMP
+INSERT INTO sal_emp
VALUES ('Bill',
'{10000, 10000, 10000, 10000}',
'{{"meeting", "lunch"}, {}}');
-INSERT INTO SAL_EMP
+INSERT INTO sal_emp
VALUES ('Carol',
'{20000, 25000, 25000, 25000}',
'{{"talk", "consult"}, {"meeting"}}');
- By default, Postgres uses the "one-based" numbering
- convention for arrays -- that is, an array of n elements starts with array[1] and ends with array[n].
- Now, we can run some queries on SAL_EMP. First, we
+ Now, we can run some queries on sal_emp. 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:
@@ -63,6 +60,10 @@ SELECT name FROM sal_emp WHERE pay_by_quarter[1] <> pay_by_quarter[2];
Carol
(1 row)
+
+ Postgres uses the "one-based" numbering
+ convention for arrays --- that is, an array of n elements starts with
+ array[1] and ends with array[n].
@@ -82,8 +83,10 @@ SELECT pay_by_quarter[3] FROM sal_emp;
We can also access arbitrary slices of an array, or
- subarrays. This query retrieves the first item on
- Bill's schedule for the first two days of the week.
+ subarrays. An array slice is denoted by writing
+ "lower subscript : upper subscript" for one or more array
+ dimensions. This query retrieves the first item on
+ Bill's schedule for the first two days of the week:
SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';
@@ -93,6 +96,59 @@ SELECT schedule[1:2][1:1] FROM sal_emp WHERE name = 'Bill';
{{"meeting"},{""}}
(1 row)
+
+ We could also have written
+
+
+SELECT schedule[1:2][1] FROM sal_emp WHERE name = 'Bill';
+
+
+ with the same result.
+
+
+
+ An array value can be replaced completely:
+
+
+UPDATE sal_emp SET pay_by_quarter = '{25000,25000,27000,27000}'
+ WHERE name = 'Carol';
+
+
+ or updated at a single entry:
+
+
+UPDATE sal_emp SET pay_by_quarter[4] = 15000
+ WHERE name = 'Bill';
+
+
+ or updated in a slice:
+
+
+UPDATE sal_emp SET pay_by_quarter[1:2] = '{27000,27000}'
+ WHERE name = 'Carol';
+
+
+
+
+ It is not currently possible to resize an array value except by
+ complete replacement; for example, we couldn't change a four-
+ element array value to a five-element value with a single
+ assignment to array[5].
+
+
+
+ The syntax for CREATE TABLE allows fixed-length arrays to be
+ defined:
+
+
+CREATE TABLE tictactoe (
+ squares int4[3][3]
+);
+
+
+ However, the current implementation does not enforce the array
+ size limits --- the behavior is the same as for arrays of
+ unspecified length.