Trafodion showstats查看表的统计信息

在前面的文章中，我们了解在Trafodion中可以使用”update statistics”语句可以在表上更新统计信息，以保证执行计划的准确性，同样的，我们也可以使用”showstats”命令来查看表上的统计信息。
关于”showstats”的语法，请参考http://trafodion.incubator.apache.org/docs/sql_reference/index.html#_showstats_statement
showstats可以基于表上的一个字段或多个字段，也可以是字段的组合，或者是key相关的字段。具体语法在此不详细介绍，下面列举几个常用的showstats的例子，

1 表上没有统计信息时，显示”No Histograms”

>>showstats for table test on every column;Histogram data for Table TRAFODION.SEABASE.TESTTable ID: 4493039957384952556   Hist ID # Ints    Rowcount         UEC Colname(s)========== ====== =========== =========== ===========================No Histograms exist for the requested columns or groups--- SQL operation complete.

2 显示表统计信息概括

>>showstats for table test on every column;Histogram data for Table TRAFODION.SEABASE.TESTTable ID: 4493039957384952556   Hist ID # Ints    Rowcount         UEC Colname(s)========== ====== =========== =========== =========================== 799435282      1           1           1 SYSKEY 799435277      1           1           1 A 799435272      1           1           1 B--- SQL operation complete.

3 显示表统计信息详细,带后缀”detail”

>>showstats for table test on every column detail;Detailed Histogram data for Table TRAFODION.SEABASE.TESTTable ID: 4493039957384952556Hist ID:    799435282Column(s):  SYSKEYTotal Rows: 1Total UEC:  1Low Value:  (2259254545988670607)High Value: (2259254545988670607)Intervals:  1Number    Rowcount         UEC Boundary====== =========== =========== ======================================     0           0           0 (2259254545988670607)     1           1           1 (2259254545988670607)Hist ID:    799435277Column(s):  ATotal Rows: 1Total UEC:  1Low Value:  ('ab')High Value: ('ab')Intervals:  1Number    Rowcount         UEC Boundary====== =========== =========== ======================================     0           0           0 ('ab')     1           1           1 ('ab')Hist ID:    799435272Column(s):  BTotal Rows: 1Total UEC:  1Low Value:  ('ab')High Value: ('ab')Intervals:  1Number    Rowcount         UEC Boundary====== =========== =========== ======================================     0           0           0 ('ab')     1           1           1 ('ab')--- SQL operation complete.