Clickhouse 时区

默认设置

Clickhouse默认是读取操作系统的时区 我们可以通过操作系统命令和clickhouse的命令查看验证：

Clickhouse> select now();

SELECT now()

┌───────────────now()─┐
│ 2020-07-11 23:47:56 │
└─────────────────────┘

1 rows in set. Elapsed: 0.003 sec. 

Clickhouse> exit;
Bye.
[root@hadoop ~]# date
Sat Jul 11 23:48:01 CST 2020



此时操作系统的时区和时间是：
# timedatectl
      Local time: Sat 2020-07-11 23:49:06 CST
  Universal time: Sat 2020-07-11 15:49:06 UTC
        RTC time: Sat 2020-07-11 15:49:05
       Time zone: Asia/Shanghai (CST, +0800)
     NTP enabled: n/a
NTP synchronized: no
 RTC in local TZ: no
      DST active: n/a

操作系统的命令：
# timedatectl list-timezones
ist-timezones 列出系统上支持的时区
set-timezone 设定时区
set-time 设置时间
set-btp 设置同步ntp

示例:设置时区示例：
timedatec修改时区
timedatectl set-timezone "America/New_York"

# timedatectl set-timezone Asia/Shanghai
ntp设置：
yum -y install ntp 
systemctl enable ntpd 
systemctl start ntpd
 同步时间
ntpdate -u cn.pool.ntp.org

clickhouse提供了配置的参数选型：

1.修改设置
sudo vim /etc/clickhouse-server/config.xml

Asia/Shanghai
 由于clickhouse是俄罗斯人主导开发的，默认设置为Europe/Moscow
2.重启服务器：
sudo service clickhouse-server restart


我们可以看到选型的说明如下：
 
    

时区在日期时间相关的函数，若指定时区作为参数。在Datetime和String类型之间进行转换。
时区的指定是按照IANA标准的时区库指定的，可以在Linux系统中通过命令查询
若不指定则使用系统启动的时区。

 clickhouse相关的时区函数：

Clickhouse> select formatDateTime(now(),'%F %T') as dt,toString(toDateTime(dt),'Asia/Shanghai') as BJ_time,toString(toDateTime(dt),'America/New_York') as NY_time;

SELECT 
    formatDateTime(now(), '%F %T') AS dt,
    toString(toDateTime(dt), 'Asia/Shanghai') AS BJ_time,
    toString(toDateTime(dt), 'America/New_York') AS NY_time

┌─dt──────────────────┬─BJ_time─────────────┬─NY_time─────────────┐
│ 2020-07-12 00:13:29 │ 2020-07-12 00:13:29 │ 2020-07-11 12:13:29 │
└─────────────────────┴─────────────────────┴─────────────────────┘

1 rows in set. Elapsed: 0.006 sec. 


可以看到Clickhouse默认采用的系统的UTC


Clickhouse> select formatDateTime(now(),'%F %T') as dt,toString(toDateTime(dt,'UTC'),'Asia/Shanghai') as BJ_time,toTimeZone(toDateTime(dt,'UTC'),'Asia/Shanghai') as random_time,toString(toDateTime(dt),'Asia/Shanghai') SH_TIME,toTimeZone(toDateTime(dt),'Asia/Shanghai') SH_time,toTimeZone(toDateTime(dt,'America/New_York'), 'Asia/Hong_Kong') HK_time;

SELECT 
    formatDateTime(now(), '%F %T') AS dt,
    toString(toDateTime(dt, 'UTC'), 'Asia/Shanghai') AS BJ_time,
    toTimeZone(toDateTime(dt, 'UTC'), 'Asia/Shanghai') AS random_time,
    toString(toDateTime(dt), 'Asia/Shanghai') AS SH_TIME,
    toTimeZone(toDateTime(dt), 'Asia/Shanghai') AS SH_time,
    toTimeZone(toDateTime(dt, 'America/New_York'), 'Asia/Hong_Kong') AS HK_time

┌─dt──────────────────┬─BJ_time─────────────┬─────────random_time─┬─SH_TIME─────────────┬─────────────SH_time─┬─────────────HK_time─┐
│ 2020-07-12 00:27:25 │ 2020-07-12 08:27:25 │ 2020-07-12 08:27:25 │ 2020-07-12 00:27:25 │ 2020-07-12 00:27:25 │ 2020-07-12 12:27:25 │
└─────────────────────┴─────────────────────┴─────────────────────┴─────────────────────┴─────────────────────┴─────────────────────┘

1 rows in set. Elapsed: 0.007 sec. 

可以看到toTimeZone,与toString 的功能很像


Clickhouse> select formatDateTime(now(),'%F %T') as dt,toTypeName(toString(toDateTime(dt),'Asia/Shanghai')) SH_TIME,toTypeName(toTimeZone(toDateTime(dt),'Asia/Shanghai')) SH_time,toTypeName(toTimeZone(toDateTime(dt,'America/New_York'), 'Asia/Hong_Kong')) HK_time;

SELECT 
    formatDateTime(now(), '%F %T') AS dt,
    toTypeName(toString(toDateTime(dt), 'Asia/Shanghai')) AS SH_TIME,
    toTypeName(toTimeZone(toDateTime(dt), 'Asia/Shanghai')) AS SH_time,
    toTypeName(toTimeZone(toDateTime(dt, 'America/New_York'), 'Asia/Hong_Kong')) AS HK_time

┌─dt──────────────────┬─SH_TIME─┬─SH_time───────────────────┬─HK_time────────────────────┐
│ 2020-07-12 00:29:43 │ String  │ DateTime('Asia/Shanghai') │ DateTime('Asia/Hong_Kong') │
└─────────────────────┴─────────┴───────────────────────────┴────────────────────────────┘

1 rows in set. Elapsed: 0.002 sec. 
toTimeZone函数可以实现时区转换，通过toTypeName还可以获知字段类型，以及该字段对应的时区。

相关的函数