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Diffstat (limited to 'doc/src/sgml/array.sgml')
| -rw-r--r-- | doc/src/sgml/array.sgml | 287 |
1 files changed, 9 insertions, 278 deletions
diff --git a/doc/src/sgml/array.sgml b/doc/src/sgml/array.sgml index a7a05762de..985a92f7fa 100644 --- a/doc/src/sgml/array.sgml +++ b/doc/src/sgml/array.sgml @@ -1,4 +1,4 @@ -<!-- $Header: /cvsroot/pgsql/doc/src/sgml/array.sgml,v 1.26 2003/06/24 23:14:42 momjian Exp $ --> +<!-- $Header: /cvsroot/pgsql/doc/src/sgml/array.sgml,v 1.27 2003/06/25 21:30:25 momjian Exp $ --> <sect1 id="arrays"> <title>Arrays</title> @@ -60,74 +60,14 @@ 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. - </para> - <para> - This can lead to surprising results. For example, the result of the - previous two inserts looks like this: -<programlisting> -SELECT * FROM sal_emp; - name | pay_by_quarter | schedule --------+---------------------------+-------------------- - Bill | {10000,10000,10000,10000} | {{meeting},{""}} - Carol | {20000,25000,25000,25000} | {{talk},{meeting}} -(2 rows) -</programlisting> - Because the <literal>[2][2]</literal> element of - <structfield>schedule</structfield> is missing in each of the - <command>INSERT</command> statements, the <literal>[1][2]</literal> - element is discarded. - </para> - <note> <para> - Fixing this is on the to-do list. + 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. Fixing this is on the to-do list. </para> </note> - - <para> - The <command>ARRAY</command> expression syntax may also be used: -<programlisting> -INSERT INTO sal_emp - VALUES ('Bill', - ARRAY[10000, 10000, 10000, 10000], - ARRAY[['meeting', 'lunch'], ['','']]); - -INSERT INTO sal_emp - VALUES ('Carol', - ARRAY[20000, 25000, 25000, 25000], - ARRAY[['talk', 'consult'], ['meeting', '']]); -SELECT * FROM sal_emp; - name | pay_by_quarter | schedule --------+---------------------------+------------------------------- - Bill | {10000,10000,10000,10000} | {{meeting,lunch},{"",""}} - Carol | {20000,25000,25000,25000} | {{talk,consult},{meeting,""}} -(2 rows) -</programlisting> - Note that with this syntax, multidimensional arrays must have matching - extents for each dimension. This eliminates the missing-array-elements - problem above. For example: -<programlisting> -INSERT INTO sal_emp - VALUES ('Carol', - ARRAY[20000, 25000, 25000, 25000], - ARRAY[['talk', 'consult'], ['meeting']]); -ERROR: Multidimensional arrays must have array expressions with matching dimensions -</programlisting> - Also notice that string literals are single quoted instead of double quoted. - </para> - - <note> - <para> - The examples in the rest of this section are based on the - <command>ARRAY</command> expression syntax <command>INSERT</command>s. - </para> - </note> - </sect2> <sect2> @@ -192,30 +132,11 @@ 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 + 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; another example follows: -<programlisting> -SELECT schedule[1:2][2] FROM sal_emp WHERE name = 'Bill'; - schedule ---------------------------- - {{meeting,lunch},{"",""}} -(1 row) -</programlisting> - </para> - - <para> - Additionally, we can also access a single arbitrary array element of - a one-dimensional array with the <function>array_subscript</function> - function: -<programlisting> -SELECT array_subscript(pay_by_quarter, 2) FROM sal_emp WHERE name = 'Bill'; - array_subscript ------------------ - 10000 -(1 row) -</programlisting> + is specified. </para> <para> @@ -226,23 +147,7 @@ UPDATE sal_emp SET pay_by_quarter = '{25000,25000,27000,27000}' WHERE name = 'Carol'; </programlisting> - or using the <command>ARRAY</command> expression syntax: - -<programlisting> -UPDATE sal_emp SET pay_by_quarter = ARRAY[25000,25000,27000,27000] - WHERE name = 'Carol'; -</programlisting> - - <note> - <para> - Anywhere you can use the <quote>curly braces</quote> array syntax, - you can also use the <command>ARRAY</command> expression syntax. The - remainder of this section will illustrate only one or the other, but - not both. - </para> - </note> - - An array may also be updated at a single element: + or updated at a single element: <programlisting> UPDATE sal_emp SET pay_by_quarter[4] = 15000 @@ -255,14 +160,6 @@ UPDATE sal_emp SET pay_by_quarter[4] = 15000 UPDATE sal_emp SET pay_by_quarter[1:2] = '{27000,27000}' WHERE name = 'Carol'; </programlisting> - - A one-dimensional array may also be updated with the - <function>array_assign</function> function: - -<programlisting> -UPDATE sal_emp SET pay_by_quarter = array_assign(pay_by_quarter, 4, 15000) - WHERE name = 'Bill'; -</programListing> </para> <para> @@ -282,88 +179,6 @@ UPDATE sal_emp SET pay_by_quarter = array_assign(pay_by_quarter, 4, 15000) </para> <para> - An array can also be enlarged by using the concatenation operator, - <command>||</command>. -<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) -</programlisting> - - The concatenation operator allows a single element to be pushed on to the - beginning or end of a one-dimensional array. It also allows two - <replaceable>N</>-dimensional arrays, or an <replaceable>N</>-dimensional - and an <replaceable>N+1</>-dimensional array. In the former case, the two - <replaceable>N</>-dimension arrays become outer elements of an - <replaceable>N+1</>-dimensional array. In the latter, the - <replaceable>N</>-dimensional array is added as either the first or last - outer element of the <replaceable>N+1</>-dimensional array. - - The array is extended in the direction of the push. Hence, by pushing - onto the beginning of an array with a one-based subscript, a zero-based - subscript array is created: - -<programlisting> -SELECT array_dims(t.f) FROM (SELECT 1 || ARRAY[2,3] AS f) AS t; - array_dims ------------- - [0:2] -(1 row) -</programlisting> - </para> - - <para> - An array can also be enlarged by using the functions - <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: - -<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}} -</programlisting> - </para> - - <para> The syntax for <command>CREATE TABLE</command> allows fixed-length arrays to be defined: @@ -379,16 +194,6 @@ CREATE TABLE tictactoe ( </para> <para> - An alternative syntax for one-dimensional arrays may be used. - <structfield>pay_by_quarter</structfield> could have been defined as: -<programlisting> - pay_by_quarter integer ARRAY[4], -</programlisting> - This syntax may <emphasis>only</emphasis> be used with the integer - constant to denote the array size. - </para> - - <para> 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 @@ -495,72 +300,6 @@ SELECT * FROM sal_emp WHERE pay_by_quarter **= 10000; is not ignored, however: after skipping leading whitespace, everything up to the next right brace or delimiter is taken as the item value. </para> - - <para> - As illustrated earlier in this chapter, arrays may also be represented - using the <command>ARRAY</command> expression syntax. This 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 the keyword - <command>ARRAY</command> and square brackets (<literal>[</> and - <literal>]</>) around the array values, plus delimiter characters between - adjacent items. The delimiter character is always a comma (<literal>,</>). - When representing multidimensional arrays, the keyword - <command>ARRAY</command> is only necessary for the outer level. For example, - <literal>'{{"hello world", "happy birthday"}}'</literal> could be written as: -<programlisting> -SELECT ARRAY[['hello world', 'happy birthday']]; - array ------------------------------------- - {{"hello world","happy birthday"}} -(1 row) -</programlisting> - or it also could be written as: -<programlisting> -SELECT ARRAY[ARRAY['hello world', 'happy birthday']]; - array ------------------------------------- - {{"hello world","happy birthday"}} -(1 row) -</programlisting> - </para> - - <para> - A final method to represent an array, is through an - <command>ARRAY</command> sub-select expression. For example: -<programlisting> -SELECT ARRAY(SELECT oid FROM pg_proc WHERE proname LIKE 'bytea%'); - ?column? -------------------------------------------------------------- - {2011,1954,1948,1952,1951,1244,1950,2005,1949,1953,2006,31} -(1 row) -</programlisting> - The sub-select may <emphasis>only</emphasis> return a single column. The - resulting one-dimensional array will have an element for each row in the - sub-select result, with an element type matching that of the sub-select's - target column. - </para> - - <para> - Arrays may be cast from one type to another in similar fashion to other - data types: - -<programlisting> -SELECT ARRAY[1,2,3]::oid[]; - array ---------- - {1,2,3} -(1 row) - -SELECT CAST(ARRAY[1,2,3] AS float8[]); - array ---------- - {1,2,3} -(1 row) -</programlisting> - - </para> - </sect2> <sect2> @@ -578,14 +317,6 @@ SELECT CAST(ARRAY[1,2,3] AS float8[]); that would otherwise be taken as array syntax or ignorable white space. </para> - <note> - <para> - The discussion in the preceding paragraph with respect to double quoting does - not pertain to the <command>ARRAY</command> expression syntax. In that case, - each element is quoted exactly as any other literal value of the element type. - </para> - </note> - <para> The array output routine will put double quotes around element values if they are empty strings or contain curly braces, delimiter characters, |