HybridDB for PostgreSQL排序键使用

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排序键是什么

排序键是表的一种属性，可以将数据按照排序键顺序存储在磁盘文件中。
排序键主要有两大优势：(1) 加速列存优化，收集的min、max元信息很少重叠，过滤性很好 (2) 对于含有order by和group by等需要排序的SQL可以避免再次排序，直接从磁盘中读取出来就是满足条件的有序数据

创建表

Command:     CREATE TABLEDescription: define a new tableSyntax:CREATE [[GLOBAL | LOCAL] {TEMPORARY | TEMP}] TABLE table_name ([ { column_name data_type [ DEFAULT default_expr ]     [column_constraint [ ... ][ ENCODING ( storage_directive [,...] ) ]]   | table_constraint   | LIKE other_table [{INCLUDING | EXCLUDING}                      {DEFAULTS | CONSTRAINTS}] ...}   [, ... ] ]   [column_reference_storage_directive [, ] ]   )   [ INHERITS ( parent_table [, ... ] ) ]   [ WITH ( storage_parameter=value [, ... ] )   [ ON COMMIT {PRESERVE ROWS | DELETE ROWS | DROP} ]   [ TABLESPACE tablespace ]   [ DISTRIBUTED BY (column, [ ... ] ) | DISTRIBUTED RANDOMLY ]   [ SORTKEY (column, [ ... ] )]   [ PARTITION BY partition_type (column)       [ SUBPARTITION BY partition_type (column) ]          [ SUBPARTITION TEMPLATE ( template_spec ) ]       [...]    ( partition_spec )        | [ SUBPARTITION BY partition_type (column) ]          [...]    ( partition_spec      [ ( subpartition_spec           [(...)]         ) ]    )

样例:

create table test(date text, time text, open float, high float, low float, volume int) with(APPENDONLY=true,ORIENTATION=column) sortkey (volume);

对表进行排序

VACUUM SORT ONLY [tablename]

修改排序键

这个命令只改catalog不会对数据立即排序，需要通过vaccum sort only命令排序。

ALTER [[GLOBAL | LOCAL] {TEMPORARY | TEMP}] TABLE table_name SET SORTKEY (column, [ ... ] )

样例:

alter table test set sortkey (high,low);

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