Codecov Report

Merging #913 into master will increase coverage by 0.10%.
The diff coverage is 76.00%.

@@            Coverage Diff             @@
##           master     #913      +/-   ##
==========================================
+ Coverage   78.37%   78.48%   +0.10%     
==========================================
  Files          40       40              
  Lines       14936    14984      +48     
==========================================
+ Hits        11706    11760      +54     
+ Misses       2538     2527      -11     
- Partials      692      697       +5     

Current syntax:

CREATE STATISTICS [IF NOT EXISTS] statistics_name
    [ '(' CARDINALITY ')' | '(' DEPENDENCY ')' | '(' CORRELATION ')' ] 
    ON table_name '(' column_name ',' column_name [',' ...] ')'

For comparison, PostgreSQL (and CockroachDB):

CREATE STATISTICS [IF NOT EXISTS] statistics_name
    [ '(' { NDISTINCT | DEPENDENCIES | MCV } [',' ...] ')' ]
    ON column_name ',' column_name [',' ...] 
    FROM table_name

Transact-SQL

CREATE STATISTICS statistics_name
    ON table_name '(' column_name ',' column_name [',' ...] ')'
    [ WHERE predicate ]
    [ WITH options ]

SAP HANA

CREATE STATISTICS statistics_name
    ON table_name [ '(' column_name ',' column_name [',' ...] ')' ] FOR { DEFAULT | EXTENDED } STORAGE
    [ TYPE statistics_type ]
    [ statistics_properties ',' statistics_properties [',' ...] ]
    [ [ NO ] INITIAL REFRESH ]

So the current syntax looks like a strange mix of PostgreSQL and Transact-SQL.

Question:

• why not allow specifying multiple statistics?

  create statistics foo (cardinality, correlation) on tbl (c1, c2);

@kennytm the idea of extended statistics is mainly borrowed from PostgreSQL, but we plan to support different types of statistics, i.e, correlation. The definition of table and columns, i.e, ON t(a,b,c) is consistent with MySQL syntax style, e.g, create index idx on t(a,b,c).

CI failure should be fixed after pingcap/tidb#18787 is merged.

@qw4990,Thanks for your review. However, LGTM is restricted to Reviewers or higher roles.See the corresponding SIG page for more information. Related SIGs: ddl(slack).

@winoros,Thanks for your review. However, LGTM is restricted to Reviewers or higher roles.See the corresponding SIG page for more information. Related SIGs: ddl(slack).