slow-query-log

long-query-time=0.00001

log-slow-verbosity=full

create table t21(a int, b int);

insert into t21 select seq, seq from seq_1_to_10000;

select sum(a) from t21 

union all

select sum(b) from t21;

# Time: 241106 16:05:31

# User@Host: root[root] @ localhost []

# Thread_id: 3  Schema: j1  QC_hit: No

# Query_time: 0.140179  Lock_time: 0.000414  Rows_sent: 2  Rows_examined: 0

# Rows_affected: 0  Bytes_sent: 81

# Pages_accessed: 48  Pages_read: 0  Pages_prefetched: 0  Pages_updated: 0  Old_rows_read: 0

# Pages_read_time: 0.0000  Engine_time: 123.8240

# Full_scan: Yes  Full_join: No  Tmp_table: No  Tmp_table_on_disk: No

# Filesort: No  Filesort_on_disk: No  Merge_passes: 0  Priority_queue: No

#

# explain: id   select_type     table   type    possible_keys   key     key_len ref     rows    r_rows  filtered        r_filtered      Extra

# explain: 1    PRIMARY t21     ALL     NULL    NULL    NULL    NULL    10157   10000.00        100.00  100.00

# explain: 2    UNION   t21     ALL     NULL    NULL    NULL    NULL    10157   10000.00        100.00  100.00

#

SET timestamp=1730901931;

select sum(a) from t21

union all

select sum(b) from t21;

select sum(a) from t21 

union

select sum(b) from t21;

# Time: 241106 16:04:59

# User@Host: root[root] @ localhost []

# Thread_id: 3  Schema: j1  QC_hit: No

# Query_time: 0.129300  Lock_time: 0.000127  Rows_sent: 1  Rows_examined: 20001

# Rows_affected: 0  Bytes_sent: 74

# Pages_accessed: 48  Pages_read: 0  Pages_prefetched: 0  Pages_updated: 0  Old_rows_read: 0

# Pages_read_time: 0.0000  Engine_time: 114.1540

# Tmp_tables: 1  Tmp_disk_tables: 0  Tmp_table_sizes: 126984

# Full_scan: Yes  Full_join: No  Tmp_table: Yes  Tmp_table_on_disk: No

# Filesort: No  Filesort_on_disk: No  Merge_passes: 0  Priority_queue: No

#

# explain: id   select_type     table   type    possible_keys   key     key_len ref     rows    r_rows  filtered        r_filtered      Extra

# explain: 1    PRIMARY t21     ALL     NULL    NULL    NULL    NULL    10000   10000.00        100.00  100.00

# explain: 2    UNION   t21     ALL     NULL    NULL    NULL    NULL    10000   10000.00        100.00  100.00

# explain: NULL UNION RESULT    <union1,2>      ALL     NULL    NULL    NULL    NULL    NULL    1.00    NULL    NULL

#

SET timestamp=1730901899;

select sum(a) from t21

union

select sum(b) from t21;