Oracle / SQL - 计算单列中值的出现次数
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Oracle / SQL - Count number of occurrences of values in a single column
提问by dscl
Okay, I probably could have come up with a better title, but wasn't sure how to word it so let me explain.
好吧，我可能想出一个更好的标题，但不知道如何措辞，所以让我解释一下。
Say I have a table with the column 'CODE'. Each record in my table will have either 'A', 'B', or 'C' as it's value in the 'CODE' column. What I would like is to get a count of how many 'A's, 'B's, and 'C's I have.
假设我有一个带有“CODE”列的表格。我表中的每条记录都将包含“A”、“B”或“C”，因为它是“CODE”列中的值。我想要的是计算我有多少个“A”、“B”和“C”。
I know I could accomplish this with 3 different queries, but I'm wondering if there is a way to do it with just 1.
我知道我可以用 3 个不同的查询来完成这个，但我想知道是否有办法只用 1 个来做到这一点。
回答by OMG Ponies
Use:
用：
SELECT t.code,
COUNT(*) AS numInstances
FROM YOUR_TABLE t
GROUP BY t.code
The output will resemble:
输出将类似于：
code numInstances
--------------------
A 3
B 5
C 1
If a code exists that has not been used, it will not show up. You'd need to LEFT JOIN to the table containing the list of codes in order to see those that don't have any references.
如果存在未使用的代码，则不会显示。您需要 LEFT JOIN 到包含代码列表的表才能查看那些没有任何引用的表。
