plan: statsInfo.count for LogicalTableDual should be its RowCount (pi…

…ngcap#6190)

executor: remove Next function for HashAggExec (pingcap#5987)

executor: remove Next for HashJoinExec (pingcap#5991)

*: move irrelevant code out of package "distsql" (pingcap#5893)

parser: create index support LOCK syntax (pingcap#5851) (pingcap#5853)

executor: use batch get to speed up LOAD DATA (pingcap#5632)

* use batch get to speed up LOAD DATA

server: optimize com_field_list, make use database faster. (pingcap#5677

) (pingcap#5679)

expression: refine the type infer of group_concat (pingcap#5582)

fix issue5462 (pingcap#5463) (pingcap#5492)

 *: improve performance of show variables (pingcap#5363)

* show: fix variable scope error (pingcap#5291)

* *: improve performance of show variables (pingcap#5297)

* *: session variable value should not be modified when get global variable (pingcap#5317)

* fix ci

* ddl,expression: make leak test more stable (pingcap#4895)