PostgreSQL 实现将多行合并转为列

CREATE TABLE Student_score(姓名 varchar, 课程 varchar, 分数 int);
INSERT INTO Student_score VALUES('张三','数学',83);
INSERT INTO Student_score VALUES('张三','物理',93);
INSERT INTO Student_score VALUES('张三','语文',80);
INSERT INTO Student_score VALUES('李四','语文',74);
INSERT INTO Student_score VALUES('李四','数学',84);
INSERT INTO Student_score VALUES('李四','物理',94);
select 姓名
  ,sum(case 课程 when '数学' then 分数 end) as 数学
  ,sum(case 课程 when '物理' then 分数 end) as 物理
  ,sum(case 课程 when '语文' then 分数 end) as 语文
from Student_score
GROUP BY 1

CREATE TABLE Student_grade(姓名 varchar, 课程 varchar, 等级 varchar);
INSERT INTO Student_grade VALUES('张三','数学','优');
INSERT INTO Student_grade VALUES('张三','物理','良');
INSERT INTO Student_grade VALUES('张三','语文','及格');
INSERT INTO Student_grade VALUES('李四','语文','及格');
INSERT INTO Student_grade VALUES('李四','数学','良');
INSERT INTO Student_grade VALUES('李四','物理','优');

  ,string_agg((case 课程 when '数学' then 等级 end),'') as 数学
  ,string_agg((case 课程 when '物理' then 等级 end),'') as 物理
  ,string_agg((case 课程 when '语文' then 等级 end),'') as 语文
from Student_grade
GROUP BY 1

SELECT *
FROM crosstab(
 'select row_name,cat,value
  from table
  order by 1,2')
AS (row_name type, category_1 type, category_2 type, category_3 type, ...);

SELECT *
FROM crosstab(
 'select 姓名,课程,分数
  from Student_score
  order by 1,2')
AS (姓名 varchar, 数学 int, 物理 int, 语文 int);

CREATE or REPLACE FUNCTION 
long_to_wide(
table_name VARCHAR,
row_name VARCHAR,
cat VARCHAR,
value_field VARCHAR)
returns void as
$$
/*
table_name : 表名
row_name : 行名字段
cat : 转换为列名的字段
value_field : 转换为值的字段
*/
DECLARE v_sql text;
arow record;
value_type VARCHAR;
BEGIN
  
  v_sql='
  drop table if exists temp_table;
  CREATE TABLE temp_table as 
  SELECT distinct '||cat||' as col from '||table_name||'
  order by '||cat;
  execute v_sql;
  v_sql='
  SELECT t.typname AS type
  FROM pg_class c
  ,pg_attribute a
  ,pg_type t 
  WHERE c.relname = lower('''||table_name||''') 
  and a.attnum > 0 
  and a.attrelid = c.oid 
  and a.atttypid = t.oid 
  and a.attname='''||value_field||'''
  ORDER BY a.attnum
  '; 
  execute v_sql into value_type;--获取值字段的数据类型
  
  v_sql='select '||row_name;
  IF value_type in ('numeric','int8','int4','int')--判断值字段是否是数值型 
    THEN  
    FOR arow in (SELECT col FROM temp_table) loop
    
    v_sql=v_sql||'
        ,sum(case '||cat||' when '''||arow.col||''' then '||value_field||' else 0 end) '||cat||'_'||arow.col;
    end loop;
  ELSE 
    FOR arow in (SELECT col FROM temp_table) loop
    
    v_sql=v_sql||'
    ,string_agg((case '||cat||' when '''||arow.col||''' then '||value_field||' else '''' end),'''') '||cat||'_'||arow.col;
    end loop;
  END IF;
    
  v_sql='
        drop table if exists '||table_name||'_wide;
        CREATE TABLE '||table_name||'_wide as 
        '||v_sql||' 
        from '||table_name||' 
        group by '||row_name||';
        drop table if exists temp_table
        ';
  
  execute v_sql;
end;
$$ LANGUAGE plpgsql;