只是一个愚蠢的例子：
表A：
- 蛋
- 面包
- 干酪
表B（当它们被吃掉时）：
- 蛋|日期
- 面包|日期
- 蛋|日期
- 奶酪|日期
- 面包|日期
对于统计数据，我需要按照每种食物类型的每个日期进行统计，如下所示：
表统计：
egg | bread | cheese
date1 2 1 0
date2 6 4 2
date3 2 0 0
我需要报表中的列标题是动态的（如果添加了新标题，则会自动显示）。
知道如何在postgres中制作这个吗？
感谢。
答案 0 :(得分：3)
基于答案Postgres dynamic column headers (from another table)（Eric Vallabh Minikel的工作）我改进了功能，使其更加灵活方便。我认为它也可能对其他人有用，特别是因为它只依赖于pg / plsql并且不需要安装扩展，因为其他的erics工作派生（即plpython）。 Testet的赔率为9.3.5，但也至少应该达到9.2。
改进：
用途：
SELECT get_crosstab_statement('table_to_pivot', ARRAY['rowname' [, <other_row_header_columns_as_well>], 'colname', 'max(cellval)');
代码：
CREATE OR REPLACE FUNCTION get_crosstab_statement(tablename character varying, row_header_columns character varying[], pivot_headers_column character varying, pivot_values character varying)
RETURNS character varying AS
$BODY$
--returns the sql statement to use for pivoting the table
--based on: http://www.cureffi.org/2013/03/19/automatically-creating-pivot-table-column-names-in-postgresql/
--based on: https://stackoverflow.com/questions/4104508/postgres-dynamic-column-headers-from-another-table
--based on: http://www.postgresonline.com/journal/categories/24-tablefunc
DECLARE
arrayname CONSTANT character varying := 'r';
row_headers_simple character varying;
row_headers_quoted character varying;
row_headers_castdown character varying;
row_headers_castup character varying;
row_header_count smallint;
row_header record;
pivot_values_columnname character varying;
pivot_values_datatype character varying;
pivot_headers_definition character varying;
pivot_headers_simple character varying;
sql_row_headers character varying;
sql_pivot_headers character varying;
sql_crosstab_result character varying;
BEGIN
-- 1. create row header definitions
row_headers_simple := array_to_string(row_header_columns, ', ');
row_headers_quoted := '''' || array_to_string(row_header_columns, ''', ''') || '''';
row_headers_castdown := array_to_string(row_header_columns, '::text, ') || '::text';
row_header_count := 0;
sql_row_headers := 'SELECT column_name, data_type
FROM information_schema.columns
WHERE table_name = ''' || tablename || ''' AND column_name IN (' || row_headers_quoted || ')';
FOR row_header IN EXECUTE sql_row_headers LOOP
row_header_count := row_header_count + 1;
row_headers_castup := COALESCE(row_headers_castup || ', ', '') || arrayname || '[' || row_header_count || ']::' || row_header.data_type || ' AS ' || row_header.column_name;
END LOOP;
-- 2. retrieve basic column name in case an aggregate function is used
SELECT coalesce(substring(pivot_values FROM '.*\((.*)\)'), pivot_values)
INTO pivot_values_columnname;
-- 3. retrieve pivot values datatype
SELECT data_type
FROM information_schema.columns
WHERE table_name = tablename AND column_name = pivot_values_columnname
INTO pivot_values_datatype;
-- 4. retrieve list of pivot column names.
sql_pivot_headers := 'SELECT string_agg(DISTINCT quote_ident(' || pivot_headers_column || '), '', '' ORDER BY quote_ident(' || pivot_headers_column || ')) as names, string_agg(DISTINCT quote_ident(' || pivot_headers_column || ') || '' ' || pivot_values_datatype || ''', '', '' ORDER BY quote_ident(' || pivot_headers_column || ') || '' ' || pivot_values_datatype || ''') as definitions FROM ' || tablename || ';';
EXECUTE sql_pivot_headers INTO pivot_headers_simple, pivot_headers_definition;
-- 5. set up the crosstab query
sql_crosstab_result := 'SELECT ' || replace (row_headers_castup || ', ' || pivot_headers_simple, ', ', ',
') || '
FROM crosstab (
''SELECT ARRAY[' || row_headers_castdown || '] AS ' || arrayname || ', ' || pivot_headers_column || ', ' || pivot_values || '
FROM ' || tablename || '
GROUP BY ' || row_headers_simple || ', ' || pivot_headers_column || (CASE pivot_values_columnname=pivot_values WHEN true THEN ', ' || pivot_values ELSE '' END) || '
ORDER BY ' || row_headers_simple || '''
,
''SELECT DISTINCT ' || pivot_headers_column || '
FROM ' || tablename || '
ORDER BY ' || pivot_headers_column || '''
) AS newtable (
' || arrayname || ' varchar[]' || ',
' || replace(pivot_headers_definition, ', ', ',
') || '
);';
RETURN sql_crosstab_result;
END
$BODY$
LANGUAGE plpgsql STABLE
COST 100;
答案 1 :(得分：2)
我遇到了同样的问题，并找到了另一种解决方案。我想在这里征求意见。
我们的想法是动态地为crosstab创建“输出类型”字符串。 plpgsql函数不能返回最终结果，因为该函数需要具有静态返回类型（我们没有）或返回setof record，因此没有优势原始的crosstab函数。因此，我的函数将输出交叉表保存在视图中。同样，尚未采用跨表格式的“pivot”数据输入表取自现有视图或表格。
使用就像这样，使用你的例子（我添加了“fat”字段来说明排序功能）：
CREATE TABLE food_fat (name character varying(20) NOT NULL, fat integer);
CREATE TABLE eaten (food character varying(20) NOT NULL, day date NOT NULL);
-- This view will be formatted as cross-table.
-- ORDER BY is important, otherwise crosstab won't merge rows
CREATE TEMPORARY VIEW mymeals AS
SELECT day,food,COUNT(*) AS meals FROM eaten
GROUP BY day, food ORDER BY day;
SELECT auto_crosstab_ordered('mymeals_cross',
'mymeals', 'day', 'food', 'meals', -- what table to convert to cross-table
'food_fat', 'name', 'fat'); -- where to take the columns from
最后一个语句创建一个如下所示的视图mymeals_cross：
SELECT * FROM mymeals_cross;
day | bread | cheese | eggs
------------+-------+--------+------
2012-06-01 | 3 | 3 | 2
2012-06-02 | 2 | 1 | 3
(2 rows)
我的实现来了：
-- FUNCTION get_col_type(tab, col)
-- returns the data type of column <col> in table <tab> as string
DROP FUNCTION get_col_type(TEXT, TEXT);
CREATE FUNCTION get_col_type(tab TEXT, col TEXT, OUT ret TEXT)
AS $BODY$ BEGIN
EXECUTE $f$
SELECT atttypid::regtype::text
FROM pg_catalog.pg_attribute
WHERE attrelid='$f$||quote_ident(tab)||$f$'::regclass
AND attname='$f$||quote_ident(col)||$f$'
$f$ INTO ret;
END;
$BODY$ LANGUAGE plpgsql;
-- FUNCTION get_crosstab_type(tab, row, val, cattab, catcol, catord)
--
-- This function generates the output type expression for the crosstab(text, text)
-- function from the PostgreSQL tablefunc module when the "categories"
-- (cross table column labels) can be looked up in some view or table.
--
-- See auto_crosstab below for parameters
DROP FUNCTION get_crosstab_type(TEXT, TEXT, TEXT, TEXT, TEXT, TEXT);
CREATE FUNCTION get_crosstab_type(tab TEXT, rw TEXT, val TEXT, cattab TEXT,
catcol TEXT, catord TEXT, OUT ret TEXT)
AS $BODY$ BEGIN
EXECUTE $f$
SELECT '"$f$||quote_ident(rw)||$f$" $f$
||get_col_type(quote_ident(tab), quote_ident(rw))||$f$'
|| string_agg(',"'||_values._v||'" $f$
||get_col_type(quote_ident(tab), quote_ident(val))||$f$')
FROM (SELECT DISTINCT ON(_t.$f$||quote_ident(catord)||$f$) _t.$f$||quote_ident(catcol)||$f$ AS _v
FROM $f$||quote_ident(cattab)||$f$ _t
ORDER BY _t.$f$||quote_ident(catord)||$f$) _values
$f$ INTO ret;
END; $BODY$ LANGUAGE plpgsql;
-- FUNCTION auto_crosstab_ordered(view_name, tab, row, cat, val, cattab, catcol, catord)
--
-- This function creates a VIEW containing a cross-table of input table.
-- It fetches the column names of the cross table ("categories") from
-- another table.
--
-- view_name - name of VIEW to be created
-- tab - input table. This table / view must have 3 columns:
-- "row", "category", "value".
-- row - column name of the "row" column
-- cat - column name of the "category" column
-- val - column name of the "value" column
-- cattab - another table holding the possible categories
-- catcol - column name in cattab to use as column label in the cross table
-- catord - column name in cattab to sort columns in the cross table
DROP FUNCTION auto_crosstab_ordered(TEXT, TEXT, TEXT, TEXT, TEXT, TEXT, TEXT, TEXT);
CREATE FUNCTION auto_crosstab_ordered(view_name TEXT, tab TEXT, rw TEXT,
cat TEXT, val TEXT, cattab TEXT, catcol TEXT, catord TEXT) RETURNS void
AS $BODY$ BEGIN
EXECUTE $f$
CREATE VIEW $f$||quote_ident(view_name)||$f$ AS
SELECT * FROM crosstab(
'SELECT $f$||quote_ident(rw)||$f$,
$f$||quote_ident(cat)||$f$,
$f$||quote_ident(val)||$f$
FROM $f$||quote_ident(tab)||$f$',
'SELECT DISTINCT ON($f$||quote_ident(catord)||$f$) $f$||quote_ident(catcol)||$f$
FROM $f$||quote_ident(cattab)||$f$ m
ORDER BY $f$||quote_ident(catord)||$f$'
) AS ($f$||get_crosstab_type(tab, rw, val, cattab, catcol, catord)||$f$)$f$;
END; $BODY$ LANGUAGE plpgsql;
-- FUNCTION auto_crosstab(view_name, tab, row, cat, val)
--
-- This function creates a VIEW containing a cross-table of input table.
-- It fetches the column names of the cross table ("categories") from
-- DISTINCT values of the 2nd column of the input table.
--
-- view_name - name of VIEW to be created
-- tab - input table. This table / view must have 3 columns:
-- "row", "category", "value".
-- row - column name of the "row" column
-- cat - column name of the "category" column
-- val - column name of the "value" column
DROP FUNCTION auto_crosstab(TEXT, TEXT, TEXT, TEXT, TEXT);
CREATE FUNCTION auto_crosstab(view_name TEXT, tab TEXT, rw TEXT, cat TEXT, val TEXT) RETURNS void
AS $$ BEGIN
PERFORM auto_crosstab_ordered(view_name, tab, rw, cat, val, tab, cat, cat);
END; $$ LANGUAGE plpgsql;
答案 2 :(得分：1)
代码运行正常。您将收到输出作为动态查询。
CREATE OR REPLACE FUNCTION public.pivotcode(tablename character varying, rowc character varying, colc character varying, cellc character varying, celldatatype character varying)
RETURNS character varying AS
$BODY$
declare
dynsql1 varchar;
dynsql2 varchar;
columnlist varchar;
begin
-- 1. retrieve list of column names.
dynsql1 = 'select string_agg(distinct ''_''||'||colc||'||'' '||celldatatype||''','','' order by ''_''||'||colc||'||'' '||celldatatype||''') from '||tablename||';';
execute dynsql1 into columnlist;
-- 2. set up the crosstab query
--create temp table temp as
dynsql2 = 'select * from crosstab ( ''select '||rowc||','||colc||','||cellc||' from '||tablename||' group by 1,2 order by 1,2'', ''select distinct '||colc||' from '||tablename||' order by 1'' ) as newtable ( '||rowc||' varchar,'||columnlist||' );';
return dynsql2;
end
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
答案 3 :(得分：0)
这是旋转数据的一个示例 - 在postgreSQL 9中有一个交叉表函数可以执行此操作：http://www.postgresql.org/docs/current/static/tablefunc.html
答案 4 :(得分：0)
我在下面的文章中解决了这个问题：
http://okbob.blogspot.com/2008/08/using-cursors-for-generating-cross.html
简而言之，我使用的函数为查询中的每个结果动态创建下一个查询的值，并返回作为refcursor所需的结果。这解决了我的sql结果部分，现在我需要弄清楚java部分，但这与问题没有多大联系：）