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Postgresql 动态统计某一列的某一值出现的次数实例

时间:2021-04-04 22:53     来源/作者:AnAnDawn

实例解析:

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select to_char(log.date, 'yyyy-MM-dd HH24') as hour,
  log.exten, sum(case log.grade when '1' then 1 else 0 end) as "1",
  sum(case log.grade when '2' then 1 else 0 end) as "2",
  sum(case log.grade when '3' then 1 else 0 end) as "3",
  sum(case log.grade when '4' then 1 else 0 end) as "4",
  sum(case log.grade when '5' then 1 else 0 end) as "5",
  log.direction from iface_satisfaction_investigation as log
where log.date >= '2017-08-03 00:00:00' and log.date < '2017-08-04 00:00:00'
group by hour,log.exten,log.direction order by hour,log.exten,log.direction asc

to_char:用于查询时间格式化,to_char(log.date, 'yyyy-MM-dd HH24'),大致的结果是:2017-08-03 13

sum():毫无疑问是用来计算总和的。

sum(case log.grade when '1' then 1 else 0 end) 是计算什么呢?

他的意思就是:

计算grade这个列的值为1的时候有多少行,后面的sum(……)就类推了。

其他的也没有什么好讲的了

补充:PostgreSQL常用的统计信息

我就废话不多说了,大家还是直接看代码吧~

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/*计算表的空间大小*/
select oid,table_schema as "模式",
    table_name as "表名",
    row_estimate::bigint as "表中的行数(估计值)",
    pg_size_pretty(total_bytes) as "总大小",
  pg_size_pretty(table_bytes) as "表大小",
    pg_size_pretty(index_bytes) as "索引大小",
  pg_size_pretty(toast_bytes) as "toast表总大小"
from (
    select *, total_bytes-index_bytes-coalesce(toast_bytes,0) as table_bytes
        from (
            select
                c.oid,
                nspname as table_schema,
                relname as table_name,
                c.reltuples as row_estimate,
                pg_total_relation_size(c.oid) as total_bytes,
                pg_indexes_size(c.oid) as index_bytes,
                pg_total_relation_size(reltoastrelid) as toast_bytes
            from pg_class c
            left join pg_namespace n on n.oid = c.relnamespace
            where relkind = 'r'
 ) t1
) t2 order by 2,3;
/*统计用户表信息*/
select
    schemaname as "模式",
    relname as "表名",
    seq_scan as "顺序扫描的次数",
    seq_tup_read as "顺序扫描获取活动行的数量",
    idx_scan as "索引扫描次数",
    idx_tup_fetch as "索引扫描获取活动行的数量",
    n_tup_ins as "累计插入的行数",
    n_tup_upd as "累计更新的行数(包含HOT 更新的行)",
    n_tup_del as "累计删除的行数",
    n_live_tup as "当前活动行估计数量",
    n_dead_tup as "当前死亡行的估计数量",
    n_mod_since_analyze as "最后一次分析后被修改的行估计数量",
    last_vacuum as "上次被手动清理的时间(不统计VACUUM FULL)",
    last_autovacuum as "上次自动清理的时间",
    last_analyze as "上次手动分析的时间",
    last_autoanalyze as "上次自动清理分析的时间",
    vacuum_count as "手动清理的次数",
    autovacuum_count as "自动清理的次数",
    analyze_count as "手动分析的次数",
    autoanalyze_count as "自动分析的次数",
    pg_size_pretty(pg_table_size(relid)) as "表大小(不包含索引)"
from pg_stat_user_tables
order by 1;
/*统计用户表IO信息*/
select
    schemaname as "模式",
    relname as "表名",
    heap_blks_read as "读取的磁盘块数量",
    heap_blks_hit as "缓冲区命中数量",
    idx_blks_read as "表上所有索引读取的磁盘块数",
    idx_blks_hit as "表上的所有索引缓冲区命中数量",
    toast_blks_read as "TOAST表(如果有)读取的磁盘块数",
    toast_blks_hit as "TOAST表(如果有)缓冲区命中数量",
    tidx_blks_read as "TOAST表索引(如果有)读取的磁盘块数",
    tidx_blks_hit as "TOAST表索引(如果有)缓冲区命中数量"
from pg_statio_user_tables
order by 1;
/*统计用户索引信息*/
select
    indexrelid,
    schemaname as "模式",
    relname as "索引所在的表名称",
    indexrelname as "索引名称",
    idx_scan as "索引扫描次数",
    idx_tup_read as "索引扫描返回的索引项数量",
    idx_tup_fetch as "简单索引扫描获取的活动行数量",
    pg_size_pretty(pg_relation_size(indexrelid)) as "索引大小"
from pg_stat_user_indexes
order by 1,2;
/*追踪函数,需要打开track_functions参数(默认关闭)*/
select * from pg_stat_user_functions;

以上为个人经验,希望能给大家一个参考,也希望大家多多支持服务器之家。如有错误或未考虑完全的地方,望不吝赐教。

原文链接:https://blog.csdn.net/qq_34090008/article/details/76618335

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