Query with conditional JOIN running slow
I have a query the first part of which looks like this -
With CTE AS (
select DISTINCT
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
OR
B.col3= 'Y' and B.col4=A.col4
OR
.
.
.
.
)
)
Now this query runs for more than 4 minutes and the execution plan showed a table spool which was data size of 600 MB and looked like this -
I changed this to conditional JOIN to UNIONs -
With CTE AS (
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
)
UNION
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'Y' and B.col4=A.col4
)
UNION
.
.
.
)
Now the spool with the large number of rows vanished and the run time reduced to 17 seconds. However when I check the IO statistics, the logical reads are higher than the previous slower query. What could the reason be ?
sql-server-2014 join execution-plan statistics union
asked Aug 13 '18 at 4:10
virvir
112
bumped to the homepage by Community♦ 7 mins ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
add a comment |
I have a query the first part of which looks like this -
With CTE AS (
select DISTINCT
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
OR
B.col3= 'Y' and B.col4=A.col4
OR
.
.
.
.
)
)
Now this query runs for more than 4 minutes and the execution plan showed a table spool which was data size of 600 MB and looked like this -
I changed this to conditional JOIN to UNIONs -
With CTE AS (
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
)
UNION
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'Y' and B.col4=A.col4
)
UNION
.
.
.
)
Now the spool with the large number of rows vanished and the run time reduced to 17 seconds. However when I check the IO statistics, the logical reads are higher than the previous slower query. What could the reason be ?
sql-server-2014 join execution-plan statistics union
asked Aug 13 '18 at 4:10
virvir
112
bumped to the homepage by Community♦ 7 mins ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
add a comment |
I have a query the first part of which looks like this -
With CTE AS (
select DISTINCT
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
OR
B.col3= 'Y' and B.col4=A.col4
OR
.
.
.
.
)
)
Now this query runs for more than 4 minutes and the execution plan showed a table spool which was data size of 600 MB and looked like this -
I changed this to conditional JOIN to UNIONs -
With CTE AS (
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
)
UNION
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'Y' and B.col4=A.col4
)
UNION
.
.
.
)
Now the spool with the large number of rows vanished and the run time reduced to 17 seconds. However when I check the IO statistics, the logical reads are higher than the previous slower query. What could the reason be ?
sql-server-2014 join execution-plan statistics union
asked Aug 13 '18 at 4:10
virvir
112
I have a query the first part of which looks like this -
With CTE AS (
select DISTINCT
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
OR
B.col3= 'Y' and B.col4=A.col4
OR
.
.
.
.
)
)
Now this query runs for more than 4 minutes and the execution plan showed a table spool which was data size of 600 MB and looked like this -
I changed this to conditional JOIN to UNIONs -
With CTE AS (
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'X' and B.col4=A.col3
)
UNION
select
A.col1,
A.col2,
.
.
.
from tableA A
JOIN tableB B ON
(
B.col3= 'Y' and B.col4=A.col4
)
UNION
.
.
.
)
Now the spool with the large number of rows vanished and the run time reduced to 17 seconds. However when I check the IO statistics, the logical reads are higher than the previous slower query. What could the reason be ?
sql-server-2014 join execution-plan statistics union
sql-server-2014 join execution-plan statistics union
asked Aug 13 '18 at 4:10
virvir
112
asked Aug 13 '18 at 4:10
virvir
112
asked Aug 13 '18 at 4:10
virvir
112
asked Aug 13 '18 at 4:10
virvir
112
asked Aug 13 '18 at 4:10
virvir
112
112
bumped to the homepage by Community♦ 7 mins ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
bumped to the homepage by Community♦ 7 mins ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
The reason is that AND and OR has the same precedence and the long condition x AND y OR z AND w OR v AND... without round brackets has a bit different meaning than you think.
Your query can be rewritten that way:
FROM tableA AS A
JOIN tableB AS B ON ( B.col3 = 'X' AND B.col4 = A.col3 )
OR ( B.col3 = 'Y' AND B.col4 = A.col4 )
OR (. . . . .)
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
I've tried this too and got the same run time and statistics(and plan) as the first query(the one with the spool with 29 million rows). And I think AND has precedence over OR.
– vir
Aug 13 '18 at 4:45
ANDandORactually have different precedence. In absence of brackets,ANDhas higher priority. YourONpredicate, therefore, would work the same way with or without those brackets. That said, however, specifying the brackets makes the intent clearer, as not everyone can constantly remember the precedence rules.
– Andriy M
Aug 13 '18 at 12:38
add a comment |
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1 Answer
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1 Answer
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active
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oldest
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active
oldest
votes
The reason is that AND and OR has the same precedence and the long condition x AND y OR z AND w OR v AND... without round brackets has a bit different meaning than you think.
Your query can be rewritten that way:
FROM tableA AS A
JOIN tableB AS B ON ( B.col3 = 'X' AND B.col4 = A.col3 )
OR ( B.col3 = 'Y' AND B.col4 = A.col4 )
OR (. . . . .)
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
I've tried this too and got the same run time and statistics(and plan) as the first query(the one with the spool with 29 million rows). And I think AND has precedence over OR.
– vir
Aug 13 '18 at 4:45
ANDandORactually have different precedence. In absence of brackets,ANDhas higher priority. YourONpredicate, therefore, would work the same way with or without those brackets. That said, however, specifying the brackets makes the intent clearer, as not everyone can constantly remember the precedence rules.
– Andriy M
Aug 13 '18 at 12:38
add a comment |
The reason is that AND and OR has the same precedence and the long condition x AND y OR z AND w OR v AND... without round brackets has a bit different meaning than you think.
Your query can be rewritten that way:
FROM tableA AS A
JOIN tableB AS B ON ( B.col3 = 'X' AND B.col4 = A.col3 )
OR ( B.col3 = 'Y' AND B.col4 = A.col4 )
OR (. . . . .)
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
I've tried this too and got the same run time and statistics(and plan) as the first query(the one with the spool with 29 million rows). And I think AND has precedence over OR.
– vir
Aug 13 '18 at 4:45
ANDandORactually have different precedence. In absence of brackets,ANDhas higher priority. YourONpredicate, therefore, would work the same way with or without those brackets. That said, however, specifying the brackets makes the intent clearer, as not everyone can constantly remember the precedence rules.
– Andriy M
Aug 13 '18 at 12:38
add a comment |
The reason is that AND and OR has the same precedence and the long condition x AND y OR z AND w OR v AND... without round brackets has a bit different meaning than you think.
Your query can be rewritten that way:
FROM tableA AS A
JOIN tableB AS B ON ( B.col3 = 'X' AND B.col4 = A.col3 )
OR ( B.col3 = 'Y' AND B.col4 = A.col4 )
OR (. . . . .)
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
The reason is that AND and OR has the same precedence and the long condition x AND y OR z AND w OR v AND... without round brackets has a bit different meaning than you think.
Your query can be rewritten that way:
FROM tableA AS A
JOIN tableB AS B ON ( B.col3 = 'X' AND B.col4 = A.col3 )
OR ( B.col3 = 'Y' AND B.col4 = A.col4 )
OR (. . . . .)
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
answered Aug 13 '18 at 4:38
KondybasKondybas
2,646912
2,646912
I've tried this too and got the same run time and statistics(and plan) as the first query(the one with the spool with 29 million rows). And I think AND has precedence over OR.
– vir
Aug 13 '18 at 4:45
ANDandORactually have different precedence. In absence of brackets,ANDhas higher priority. YourONpredicate, therefore, would work the same way with or without those brackets. That said, however, specifying the brackets makes the intent clearer, as not everyone can constantly remember the precedence rules.
– Andriy M
Aug 13 '18 at 12:38
add a comment |
I've tried this too and got the same run time and statistics(and plan) as the first query(the one with the spool with 29 million rows). And I think AND has precedence over OR.
– vir
Aug 13 '18 at 4:45
ANDandORactually have different precedence. In absence of brackets,ANDhas higher priority. YourONpredicate, therefore, would work the same way with or without those brackets. That said, however, specifying the brackets makes the intent clearer, as not everyone can constantly remember the precedence rules.
– Andriy M
Aug 13 '18 at 12:38
I've tried this too and got the same run time and statistics(and plan) as the first query(the one with the spool with 29 million rows). And I think AND has precedence over OR.
– vir
Aug 13 '18 at 4:45
I've tried this too and got the same run time and statistics(and plan) as the first query(the one with the spool with 29 million rows). And I think AND has precedence over OR.
– vir
Aug 13 '18 at 4:45
AND and OR actually have different precedence. In absence of brackets, AND has higher priority. Your ON predicate, therefore, would work the same way with or without those brackets. That said, however, specifying the brackets makes the intent clearer, as not everyone can constantly remember the precedence rules.– Andriy M
Aug 13 '18 at 12:38
AND and OR actually have different precedence. In absence of brackets, AND has higher priority. Your ON predicate, therefore, would work the same way with or without those brackets. That said, however, specifying the brackets makes the intent clearer, as not everyone can constantly remember the precedence rules.– Andriy M
Aug 13 '18 at 12:38
add a comment |
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