COUNT

返回资源中的记录总数，或分组中某列非 NULL 实例的计数。

另请参阅：
[SELECT]

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语法

SELECT COUNT( * | columnExpression ) FROM <multipartIdentifier>
[ GROUP BY groupByColumn ];

参数

columnExpression 或 *
列或表达式。如果指定 *，则统计资源或分组中的所有记录。

columnExpression 中必须至少有一个值不为 NULL，否则返回 NULL。

groupByColumn
用于执行汇总或聚合操作的一列或多列。GROUP BY 子句为每个列分组返回一行。

返回值

返回一个整数，表示计数。

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示例

返回列表达式在整个资源上的平均值

SELECT count(*) as num_instances
FROM google.compute.instances 
WHERE project = 'stackql-demo' 
AND zone = 'australia-southeast1-a';

返回按另一个列表达式分组的列表达式的平均值

SELECT tags, count(*) as num_instances
FROM google.compute.instances 
WHERE project = 'stackql-demo' 
AND zone = 'australia-southeast1-a'
GROUP BY json_extract(tags, '$.instanceType');

将 COUNT 用作窗口函数来计算累计计数

-- Track cumulative issue counts over time
SELECT
    number,
    title,
    state,
    created_at,
    COUNT(*) OVER (ORDER BY created_at) as cumulative_issues,
    COUNT(*) OVER (PARTITION BY state ORDER BY created_at) as cumulative_by_state
FROM github.issues.issues
WHERE owner = 'stackql'
  AND repo = 'stackql'
ORDER BY created_at;

有关更多信息，请参阅 https://www.sqlite.org/lang_aggfunc.html#count。