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  • Postgresql 动态统计某一列的某一值出现的次数实例
  • 2021/1/26 15:09:06
  • 实例解析:

    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~

    /*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本教程网。如有错误或未考虑完全的地方,望不吝赐教。