PostgreSQL中的条件求和

Question

我有一个transactions表，其中包含类别（category_id），金额（amount）和标志（managed），可以是true或false。

我想显示所有类别的列表，其中包含托管和非托管交易的总金额，例如

Category | managed_transactions | unmanaged_transactions
Cat 1    |     124000           |     54000
Cat 2    |     4000             |     0
Cat 3    |     854000           |     1000000

有没有办法做类似

的事情

Select category_id,
       sum(amount) if (managed is true) as managed_transactions,
       sum(amount) if (managed is false) as unmanaged_transactions
from transactions

我显然被困在if managed is true部分......

Answer 1

享受！

SELECT
  category_id,
  SUM( CASE WHEN managed THEN amount ELSE      0 END ) AS managed_transactions,
  SUM( CASE WHEN managed THEN      0 ELSE amount END ) AS unmanaged_transactions
FROM
  transactions
GROUP BY
  category_id
ORDER BY
  category_id