SQL Server獲取行數

Question

我有一個名爲replies的表，它有一個名爲topic_id的列。

我想要做的是計算有多少行具有topic_id 1.

我試圖

SELECT COUNT(*) 
FROM [***].[replies] 
WHERE [***].[topic_id] = '1' 

但在這種情況下，我不知道這是否是一個有效的查詢。如果是這樣，我怎樣才能將它拉回到我的php代碼中名爲$num_rows的變量中？

說明：*實際上是我介紹的前綴。

Answer 1

像這樣的東西應該工作：

--declare the variable 
DECLARE @num_rows INT 

--get the total number of rows 
SELECT @num_rows = COUNT(*) FROM replies WHERE topic_id = 1 

--get a distinct count of rows (if for some reason you need it) 
SELECT @num_rows = COUNT(DISTINCT reply_id) FROM replies WHERE topic_id = 1 

--return the result set 
SELECT @num_rows AS num_rows 

如果你只是想返回一個名爲num_rows雖然列，這將是一個更有效的方法：

SELECT COUNT(*) AS num_rows FROM replies WHERE topic_id = 1