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_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_tablesorder 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_tablesorder 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_indexesorder 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
