英文:
How do I count the number of records in a Cassandra table using the GoCQL driver?
问题
我想用Go语言（最好使用GoCql）编写一个简单的程序来计算Cassandra表中记录的数量，这样我就可以减少一次性对数据库的负载量，并降低超时的概率。我只想计算带有where子句的元素数量。
如果可能的话，请简要提供答案，因为我是一个完全的新手。这将对我有很大帮助。
比如，查询给定userId的用户订单数量的查询语句可以是：
Select * from KeySpace.OrderTable where userid = userId
英文:
I wanted write a simple program in golang (prefer GoCql) to count the number of records in a Cassandra table. so I can reduce the amount of load on db at a time and reduce the probability of timeouts. I just wanted to count the number of elements with where clause.
Please suggest the answers in brief if possible, I'm a complete newbie. It will help me a lot.
Like a query of count number of order of a user with a given userId
Select * from KeySpace.OrderTable where userid = userId
答案1
得分: 1
这是一个非常简化的应用程序，使用GoCQL驱动程序计算system.local表中local分区的行数：
package main
import (
"fmt"
"github.com/gocql/gocql"
)
func main() {
// 连接到本地运行的Cassandra集群
cluster := gocql.NewCluster("127.0.0.1:9042")
session, _ := cluster.CreateSession()
iter := session.Query(`SELECT COUNT(version) FROM system.local WHERE key = 'local'`).Iter()
for iter.Scan(&rows) {
fmt.Printf("%d rows\n", rows)
}
}
请记住，你只应该计算分区内的行数。不受限制的查询（不限于分区键）将执行完整的表扫描，这是昂贵的，正如我在为什么在Cassandra中使用COUNT()是不好的中所记录的那样。祝好！
英文:
Here's an extremely simplified app that counts the number of rows in the system.local table for the partition local using the GoCQL driver:
package main
import (
"fmt"
"github.com/gocql/gocql"
)
func main() {
// connect to a Cassandra cluster running locally
cluster := gocql.NewCluster("127.0.0.1:9042")
session, _ := _cluster.CreateSession()
iter := session.Query(`SELECT COUNT(version) FROM system.local WHERE key = 'local'`).Iter()
for iter.Scan(&rows) {
fmt.Printf("%d rows\n", rows)
}
}
Just remember that you should only count rows within a partition. Unbounded queries (not restricted to a partition key) will do a full table scan which is expensive as I've documented in Why COUNT() is bad in Cassandra. Cheers!
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