如何構建一個查詢來返回一個結果

Question

在谷歌的bigquery，讓我說我想嘗試找到一個完全匹配（例如：通過郵政編碼），但如果我失敗了，根據說城市+狀態得到另一個更接近的匹配+國家。

因此，像：

select * 
from locations 
where 
    Target_Type = "Postal Code" and 
    Name = "L4A" and 
    Country_Code = "CA" 
    or 
    (
    Name = "Toronto" and 
    Target_Type = "City" and 
    Country_Code = "CA" 
) 

這將返回兩個，我想只是第一場比賽，第二隻在第一場比賽失敗。

如何做到這一點？

Answer 1

創建一個虛擬字段以指示哪一個具有更高的優先級。並使用UNION同時進行搜索。

SELECT '1st Match' as priority, <some fields> 
FROM YourTable 
WHERE <some conditions> 
UNION ALL 
SELECT '2st Match' as priority, <some fields> 
FROM YourTable 
WHERE <other conditions> 
ORDER BY priority, <other sort field> -- in case query return multiple result 
LIMIT 1 

Answer 2

BigQuery的標準SQL - 又一個值得考慮的選擇 - 它允許你添加更多的「規則」比只有兩個在你的榜樣

#standardSQL 
WITH locations AS (
    SELECT "Postal Code" AS Target_Type, "L4A" AS Name, "CA" AS Country_Code UNION ALL 
    SELECT "City", "Toronto", "CA" 
) 
SELECT * 
FROM locations 
WHERE (
    Target_Type = "Postal Code" AND 
    Name = "L4A" AND 
    Country_Code = "CA" 
) OR (
    Name = "Toronto" AND 
    Target_Type = "City"AND 
    Country_Code = "CA" 
) 
ORDER BY CASE Target_Type 
    WHEN "Postal Code" THEN 1 
    WHEN "City" THEN 2 
    ELSE 3 END 
LIMIT 1