如何在Postgres中将行转换为列？

-- 检查是否启用了tablefunc扩展
SELECT * FROM pg_extension WHERE extname = 'tablefunc';

-- 如果没有启用，执行以下命令启用
CREATE EXTENSION IF NOT EXISTS tablefunc;

CREATE TABLE sales (
    product_id integer,
    sales_date date,
    quantity integer
);

SELECT *
FROM crosstab(
    'SELECT product_id, sales_date, quantity 
     FROM sales 
     ORDER BY 1,2',
    'SELECT DISTINCT sales_date 
     FROM sales 
     ORDER BY 1'
)
AS sales_summary (product_id integer, date1 integer, date2 integer, date3 integer);