database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2026-01-06 05:22:24 +03:00
Code Activity

Bug#47280 - strange results from count(*) with order by multiple

Browse Source 
columns without where/group
                     
Simple SELECT with implicit grouping used to return many rows if
the query was ordered by the aggregated column in the SELECT
list. This was incorrect because queries with implicit grouping
should only return a single record.
                              
The problem was that when JOIN:exec() decided if execution needed
to handle grouping, it was assumed that sum_func_count==0 meant
that there were no aggregate functions in the query. This
assumption was not correct in JOIN::exec() because the aggregate
functions might have been optimized away during JOIN::optimize().
                  
The reason why queries without ordering behaved correctly was
that sum_func_count is only recalculated if the optimizer chooses
to use temporary tables (which it does in the ordered case).
Hence, non-ordered queries were correctly treated as grouped.
                  
The fix for this bug was to remove the assumption that
sum_func_count==0 means that there is no need for grouping. This
was done by introducing variable "bool implicit_grouping" in the
JOIN object.
This commit is contained in:
Jorgen Loland
2009-10-14 10:46:50 +02:00
parent 0ece5891a2
commit bf0aa2bd34
6 changed files with 156 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

27
sql/sql_class.h
View File

@@ -2647,7 +2647,32 @@ public:
MI_COLUMNDEF *recinfo,*start_recinfo;
KEY *keyinfo;
ha_rows end_write_records;
uint field_count,sum_func_count,func_count;
/**
Number of normal fields in the query, including those referred to
from aggregate functions. Hence, "SELECT `field1`,
SUM(`field2`) from t1" sets this counter to 2.
@see count_field_types
*/
uint field_count;
/**
Number of fields in the query that have functions. Includes both
aggregate functions (e.g., SUM) and non-aggregates (e.g., RAND).
Also counts functions referred to from aggregate functions, i.e.,
"SELECT SUM(RAND())" sets this counter to 2.
@see count_field_types
*/
uint func_count;
/**
Number of fields in the query that have aggregate functions. Note
that the optimizer may choose to optimize away these fields by
replacing them with constants, in which case sum_func_count will
need to be updated.
@see opt_sum_query, count_field_types
*/
uint sum_func_count;
uint hidden_field_count;
uint group_parts,group_length,group_null_parts;
uint quick_group;