*.: add support for alter database stmt #691

[hustjieke]

[summary] add "ALTER DATABASE Statement", For MySQL 8.0, support new option "ENCRYPTION" and "READ ONLY " and no longer support "UPGRADE DATA DIRECTORY NAME" feature in 5.7. see:https://dev.mysql.com/doc/refman/8.0/en/alter-database.html

ALTER {DATABASE | SCHEMA} [db_name]
    alter_option ...

alter_option: {
    [DEFAULT] CHARACTER SET [=] charset_name
  | [DEFAULT] COLLATE [=] collation_name
  | [DEFAULT] ENCRYPTION [=] {'Y' | 'N'}
  | READ ONLY [=] {DEFAULT | 0 | 1}
}

[test case] src/proxy/ddl_test.go src/vendor/github.com/xelabs/go-mysqlstack/sqlparser/ddl_test.go

[patch codecov] src/proxy/ddl.go 93.9% src/vendor/github.com/xelabs/go-mysqlstack/sqlparser/ast.go 96.8% src/vendor/github.com/xelabs/go-mysqlstack/sqlparser/ast_funcs.go 95.5%

[codecov[bot]]

Codecov Report

Merging #712 (dfbf5fe) into master (ed3d531) will increase coverage by 0%. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #712   +/-   ##
=====================================
  Coverage      89%    89%           
=====================================
  Files         131    131           
  Lines        9271   9284   +13     
=====================================
+ Hits         8254   8278   +24     
+ Misses        674    666    -8     
+ Partials      343    340    -3     

Impacted Files	Coverage Δ
src/proxy/ddl.go	91% <100%> (+<1%)	:arrow_up:
src/executor/engine/merge_join.go	96% <0%> (+1%)	:arrow_up:
src/backend/queryz.go	90% <0%> (+3%)	:arrow_up:
src/backend/pool.go	91% <0%> (+3%)	:arrow_up:
src/backend/connection.go	92% <0%> (+4%)	:arrow_up:

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[BohuTANG]

LGTM