revision-id: 85bd5314c56c150d756066806d4a6cb5b682383f (mariadb-10.1.43-251-g85bd5314c56) parent(s): ab578bdf453c3cb0e9ca561cf373f64c96b22fda author: Sergei Petrunia committer: Sergei Petrunia timestamp: 2020-08-06 13:39:10 +0300 message: Better comment about TABLE::maybe_null --- sql/table.h | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/sql/table.h b/sql/table.h index 93795113fab..2ea9b514df4 100644 --- a/sql/table.h +++ b/sql/table.h @@ -1291,9 +1291,16 @@ struct TABLE /* number of select if it is derived table */ uint derived_select_number; /* - 0 or JOIN_TYPE_{LEFT|RIGHT}. Currently this is only compared to 0. - If maybe_null !=0, this table is inner w.r.t. some outer join operation, - and null_row may be true. + Possible values: + - 0 by default + - JOIN_TYPE_{LEFT|RIGHT} if the table is inner w.r.t an outer join + operation + - 1 if the SELECT has mixed_implicit_grouping=1. example: + select max(col1), col2 from t1. In this case, the query produces + one row with all columns having NULL values. + + Interpetation: If maybe_null!=0, all fields of the table are considered + NULLable (and have NULL values when null_row=true) */ uint maybe_null; int current_lock; /* Type of lock on table */