是否可以在WHERE中使用CASE？

Question

試圖做到這一點：

SELECT CASE WHEN field = true THEN one * another ELSE one END as case_field 
FROM table WHERE case_field >= 9000 

和接收case_field不存在的錯誤。

有沒有可能做到這一點，而無需重複CASE？

Answer 1

看起來像PostgreSQL的支持derived tables

SELECT * FROM 
(
SELECT CASE WHEN field = true THEN one * another ELSE one END as case_field 
FROM table 
) AS derived 
WHERE case_field >= 9000 

您可能要檢查它不會對執行計劃的任何負面影響。

Answer 2

使用臨時表：

SELECT * 
FROM (
    SELECT 
     CASE WHEN field = true THEN one * another 
     ELSE one 
     END as case_field 
     FROM table 
    ) a 
WHERE a.case_field >= 9000