是否可以根据PostgreSQL中的输入列生成列

这可以通过许多CASE表达式来完成：

SELECT project,
       size,
       startdate,
       CASE WHEN mon < 2
            THEN greatest(size - 50 * (1 - mon), 0)
            ELSE 0
       END AS jan,
       CASE WHEN mon < 3
            THEN greatest(size - 50 * (2 - mon), 0)
            ELSE 0
       END AS feb,
       CASE WHEN mon < 4
            THEN greatest(size - 50 * (3 - mon), 0)
            ELSE 0
       END AS mar,
       CASE WHEN mon < 5
            THEN greatest(size - 50 * (4 - mon), 0)
            ELSE 0
       END AS apr,
       CASE WHEN mon < 6
            THEN greatest(size - 50 * (5 - mon), 0)
            ELSE 0
       END AS may,
       CASE WHEN mon < 7
            THEN greatest(size - 50 * (6 - mon), 0)
            ELSE 0
       END AS jun,
       CASE WHEN mon < 8
            THEN greatest(size - 50 * (7 - mon), 0)
            ELSE 0
       END AS jul,
       CASE WHEN mon < 9
            THEN greatest(size - 50 * (8 - mon), 0)
            ELSE 0
       END AS aug,
       CASE WHEN mon < 10
            THEN greatest(size - 50 * (9 - mon), 0)
            ELSE 0
       END AS sep,
       CASE WHEN mon < 11
            THEN greatest(size - 50 * (10 - mon), 0)
            ELSE 0
       END AS oct,
       CASE WHEN mon < 12
            THEN greatest(size - 50 * (11 - mon), 0)
            ELSE 0
       END AS nov,
       CASE WHEN mon < 13
            THEN greatest(size - 50 * (12 - mon), 0)
            ELSE 0
       END AS dec
FROM (SELECT project,
             size,
             startdate,
             extract(month FROM startdate) AS mon
      FROM mytable) AS q;

回答来源：stackoverflow