如何在WHERE子句中使用別名列日？

Question

我對此查詢有疑問：

  SELECT DAYOFYEAR(t.ts_start) AS 'day', YEAR(t.ts_start) AS year, t.o AS value FROM Cryptoforecast_ETH_BTC_1h AS t 

當我運行它會顯示結果。 現在我想過濾一天添加這樣的WHERE語句

SELECT DAYOFYEAR(t.ts_start) AS 'day', YEAR(t.ts_start) AS year, t.o AS value FROM Cryptoforecast_ETH_BTC_1h AS t WHERE 'day'=157

但這沒有結果和警告：

Truncated incorrect DOUBLE value: 'day'

問題是什么？

Answer 1

您不能在WHERE子句中使用別WHERE 。 因此，您實際上並沒有將列值與int進行比較。

WHERE 'day'=157

相反，您可以使用

WHERE DAYOFYEAR(t.ts_start) = 157

注意：列別名無需使用單引號。

Answer 2

只需在WHERE子句中重復調用DAYOFYEAR ：

SELECT
    DAYOFYEAR(t.ts_start) AS day,
    YEAR(t.ts_start) AS year,
    o AS value
FROM Cryptoforecast_ETH_BTC_1h
WHERE DAYOFYEAR(t.ts_start) = 157;

或者，如果要使用day別名，則可以使用重載的HAVING子句來使用：

SELECT
    DAYOFYEAR(t.ts_start) AS day,
    YEAR(t.ts_start) AS year,
    o AS value
FROM Cryptoforecast_ETH_BTC_1h
HAVING day = 157;