Re: How to optimize a slow query?
Hi Mike, Thanks for you help! Best, Jia mos wrote: Jia, The code you sent seems to be able to get the job done. You could try something simpler by executing 2 sql statements instead of using one. Something like: create table rmpdata1 select ri.*, mv.* from RItime as ri left join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)); insert into rmpdata1 select ri.*, mv.* from MVtime as mv left join RItime as ri on (ri.code=mv.code and ri.ndate=mv.ndate)) where ri.code is null and ri.date is null; You will of course have to play with the column list to avoid duplicate columns. The Insert statement will insert rows from mv that are missing in ri. Mike At 01:51 PM 9/6/2009, Jia Chen wrote: Hi Mike, Thanks for your detailed answer. Now, I understand what you mean. And, yes, I agree with you that keeping all data in one table works better for a bunch of 1:1 relationship tables. Actually, this is what I was trying to do with that query. Since you mention They all had a 1:1 relationship and occasionally some of the tables did not have a corresponding row. and From then on I've merged all 8 tables into one and if any of the subordinate table data isn't available for a row, its columns are set to NULL, I do want to ask you about how you set the columns to NULL for rows in subordinate table data unavailable because I have similar situation. If I want to combine two tables into one, I think that a full outer join can achieve what you did. However, MySQL does not have full outer join. So, I am using create table rmpdata1 (select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri left outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)) union (select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri right outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)); This query takes more than twice as much time as the query in my first e-mail. Do you have a better way? Thanks. Best, Jia mos wrote: Jia, Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. Could you elaborate that? Sure but first I have to relate it to my own experience. I had 8 tables of around 25 million rows each. They all had a 1:1 relationship and occasionally some of the tables did not have a corresponding row. I felt it was better from a design point of view to have 8 different tables and do the joins on the tables that I needed for each of my particular queries. I'd be joining anywhere from 2 to 5 or 6 or even all 8 tables at a time, using a where clause to select 15k rows at a time. This is the way to do it from a normalized point of view. All of the information is in its respective table and only assemble the tables for each particular query. Well, this was slwww! A heck of a lot of work was done to join the tables together on a 2 column key (like yours). I also had to run maintenance on the tables to see which tables where corrupted or were missing rows that should have been there. The tables also repeated columns from the other tables like date and product_id that is used to help identify each row. Well to make a long story short, it was far too much effort to juggle the relationships between all of these tables. Then a colleague made the monumental announcement by saying I've never found the need to use more than 1 table when there was a 1:1 relationship. There is a tremendous speed cost involved in piecing the data back together. I put all of the data into 1 table. So the light went on for me. From then on I've merged all 8 tables into one and if any of the subordinate table data isn't available for a row, its columns are set to NULL, which is the values they would have had anyway after a left join. I am perfectly happy know with one wide table with over 100 columns. Everything is in its place and maintenance is a dream. Queries are also quite fast because all of the information is under one table and not 8. I don't have to worry about optimizing the indexes for the table joins because there aren't any joins between these tables because it is all in 1 row. So you really have to ask yourself, why spend 10 minutes each time your query is run? Instead you eliminate the query altogether by keeping the data of the 2 tables into 1 table in the first place. Mike At 09:45 AM 9/6/2009, Jia Chen wrote: Thanks for your reply, Mike. Yes, 13419851 rows were added to rmpdata1. However, 10 minutes seem to be too long. I run the same join by using SQL procedure in a statistical software called SAS on a similar machine. It only takes 1 minute and 3 seconds. Yes, it is a 1:1 relationship between table RItime and
Re: How to optimize a slow query?
Thanks for your reply, Mike. Yes, 13419851 rows were added to rmpdata1. However, 10 minutes seem to be too long. I run the same join by using SQL procedure in a statistical software called SAS on a similar machine. It only takes 1 minute and 3 seconds. Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. Could you elaborate that? I was using B-tree index. Switching to HASH does help. Now, it takes 4 min 50.17 sec to run the query. I also turn on profiling by using mysql set profiling = 1; Query OK, 0 rows affected (0.01 sec) After the query finishes, I get mysql show profile; +--++ | Status | Duration | +--++ | starting | 0.000123 | | checking permissions | 0.10 | | Opening tables | 0.44 | | System lock | 0.07 | | Table lock | 0.11 | | init | 0.83 | | creating table | 0.003428 | | After create | 0.000124 | | System lock | 0.04 | | Table lock | 0.51 | | optimizing | 0.07 | | statistics | 0.33 | | preparing| 0.20 | | executing| 0.04 | | Sending data | 290.153530 | | end | 0.08 | | end | 0.04 | | query end| 0.03 | | freeing items| 0.10 | | closing tables | 0.25 | | logging slow query | 0.01 | | logging slow query | 0.013429 | | cleaning up | 0.04 | +--++ 23 rows in set (0.02 sec) MySQL spends most of its time sending data. According to http://dev.mysql.com/doc/refman/5.0/en/general-thread-states.html, sending data means that the thread is processing rows for a |SELECT| http://dev.mysql.com/doc/refman/5.0/en/select.html statement and also is sending data to the client. Is there more room to optimize this query? Thanks again. Best, Jia mos wrote: How many rows were added to rmpdata1 table? If it is 13.4 million rows then it is going to take several minutes to join this many rows from the 2 tables. Is there a 1:1 relationship between the two tables or a 1:Many? If there is a 1:1 then I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. The only other thing I can suggest is to change the type of index on the tables being joined to see if that makes a speed difference. For example, if you are using BTREE then switch to HASH or vice versa. See http://dev.mysql.com/doc/refman/5.0/en/create-index.html for more info. Mike At 10:05 AM 9/5/2009, Jia Chen wrote: Hi there, One simple query took more than 10 minutes. Here is how relevant rows in the slow query log looks like: # Time: 090905 10:49:57 # u...@host: root[root] @ localhost [] # Query_time: 649 Lock_time: 0 Rows_sent: 0 Rows_examined: 26758561 use world; create table rmpdata1 select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri left outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate); When I explain only the select clause, I get +--+---+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | ++-+---++---+-+-+--+--+---+ | 1 | SIMPLE | ri| ALL| NULL | NULL| NULL | NULL | 13419851 | | | 1 | SIMPLE | mv| eq_ref | PRIMARY | PRIMARY | 11 | world.ri.code,world.ri.ndate |1 | | ++-+---++---+-+-+--+--+---+ 2 rows in set (0.00 sec) I use show table status from world; to get information about two tables, RItime and MVtime, in the join clause: Name: RItime Engine: MyISAM Version: 10 Row_format: Dynamic Rows: 13419851 Avg_row_length: 31 Data_length: 427721848 Max_data_length: 281474976710655 Index_length: 347497472 Data_free: 0 Auto_increment: NULL Create_time: 2009-09-03 10:17:57 Update_time: 2009-09-03 12:04:02 Check_time: NULL Collation: latin1_swedish_ci Checksum: NULL Create_options: Comment: *** 2. row *** Name: MVtime Engine: MyISAM Version: 10 Row_format: Dynamic Rows: 13562373 Avg_row_length: 31 Data_length: 430220056 Max_data_length: 281474976710655 Index_length: 350996480 Data_free: 0 Auto_increment: NULL Create_time: 2009-09-03 13:31:33 Update_time: 2009-09-03
Re: How to optimize a slow query?
Jia, Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. Could you elaborate that? Sure but first I have to relate it to my own experience. I had 8 tables of around 25 million rows each. They all had a 1:1 relationship and occasionally some of the tables did not have a corresponding row. I felt it was better from a design point of view to have 8 different tables and do the joins on the tables that I needed for each of my particular queries. I'd be joining anywhere from 2 to 5 or 6 or even all 8 tables at a time, using a where clause to select 15k rows at a time. This is the way to do it from a normalized point of view. All of the information is in its respective table and only assemble the tables for each particular query. Well, this was slwww! A heck of a lot of work was done to join the tables together on a 2 column key (like yours). I also had to run maintenance on the tables to see which tables where corrupted or were missing rows that should have been there. The tables also repeated columns from the other tables like date and product_id that is used to help identify each row. Well to make a long story short, it was far too much effort to juggle the relationships between all of these tables. Then a colleague made the monumental announcement by saying I've never found the need to use more than 1 table when there was a 1:1 relationship. There is a tremendous speed cost involved in piecing the data back together. I put all of the data into 1 table. So the light went on for me. From then on I've merged all 8 tables into one and if any of the subordinate table data isn't available for a row, its columns are set to NULL, which is the values they would have had anyway after a left join. I am perfectly happy know with one wide table with over 100 columns. Everything is in its place and maintenance is a dream. Queries are also quite fast because all of the information is under one table and not 8. I don't have to worry about optimizing the indexes for the table joins because there aren't any joins between these tables because it is all in 1 row. So you really have to ask yourself, why spend 10 minutes each time your query is run? Instead you eliminate the query altogether by keeping the data of the 2 tables into 1 table in the first place. Mike At 09:45 AM 9/6/2009, Jia Chen wrote: Thanks for your reply, Mike. Yes, 13419851 rows were added to rmpdata1. However, 10 minutes seem to be too long. I run the same join by using SQL procedure in a statistical software called SAS on a similar machine. It only takes 1 minute and 3 seconds. Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. Could you elaborate that? I was using B-tree index. Switching to HASH does help. Now, it takes 4 min 50.17 sec to run the query. I also turn on profiling by using mysql set profiling = 1; Query OK, 0 rows affected (0.01 sec) After the query finishes, I get mysql show profile; +--++ | Status | Duration | +--++ | starting | 0.000123 | | checking permissions | 0.10 | | Opening tables | 0.44 | | System lock | 0.07 | | Table lock | 0.11 | | init | 0.83 | | creating table | 0.003428 | | After create | 0.000124 | | System lock | 0.04 | | Table lock | 0.51 | | optimizing | 0.07 | | statistics | 0.33 | | preparing| 0.20 | | executing| 0.04 | | Sending data | 290.153530 | | end | 0.08 | | end | 0.04 | | query end| 0.03 | | freeing items| 0.10 | | closing tables | 0.25 | | logging slow query | 0.01 | | logging slow query | 0.013429 | | cleaning up | 0.04 | +--++ 23 rows in set (0.02 sec) MySQL spends most of its time sending data. According to http://dev.mysql.com/doc/refman/5.0/en/general-thread-states.html, sending data means that the thread is processing rows for a |SELECT| http://dev.mysql.com/doc/refman/5.0/en/select.html statement and also is sending data to the client. Is there more room to optimize this query? Thanks again. Best, Jia mos wrote: How many rows were added to rmpdata1 table? If it is 13.4 million rows then it is going to take several minutes to join this many rows from the 2 tables. Is there a 1:1 relationship between the two tables or a 1:Many? If there is a 1:1 then I'd recommend joining the two tables into 1 table
Re: How to optimize a slow query?
Hi Mike, Thanks for your detailed answer. Now, I understand what you mean. And, yes, I agree with you that keeping all data in one table works better for a bunch of 1:1 relationship tables. Actually, this is what I was trying to do with that query. Since you mention They all had a 1:1 relationship and occasionally some of the tables did not have a corresponding row. and From then on I've merged all 8 tables into one and if any of the subordinate table data isn't available for a row, its columns are set to NULL, I do want to ask you about how you set the columns to NULL for rows in subordinate table data unavailable because I have similar situation. If I want to combine two tables into one, I think that a full outer join can achieve what you did. However, MySQL does not have full outer join. So, I am using create table rmpdata1 (select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri left outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)) union (select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri right outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)); This query takes more than twice as much time as the query in my first e-mail. Do you have a better way? Thanks. Best, Jia mos wrote: Jia, Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. Could you elaborate that? Sure but first I have to relate it to my own experience. I had 8 tables of around 25 million rows each. They all had a 1:1 relationship and occasionally some of the tables did not have a corresponding row. I felt it was better from a design point of view to have 8 different tables and do the joins on the tables that I needed for each of my particular queries. I'd be joining anywhere from 2 to 5 or 6 or even all 8 tables at a time, using a where clause to select 15k rows at a time. This is the way to do it from a normalized point of view. All of the information is in its respective table and only assemble the tables for each particular query. Well, this was slwww! A heck of a lot of work was done to join the tables together on a 2 column key (like yours). I also had to run maintenance on the tables to see which tables where corrupted or were missing rows that should have been there. The tables also repeated columns from the other tables like date and product_id that is used to help identify each row. Well to make a long story short, it was far too much effort to juggle the relationships between all of these tables. Then a colleague made the monumental announcement by saying I've never found the need to use more than 1 table when there was a 1:1 relationship. There is a tremendous speed cost involved in piecing the data back together. I put all of the data into 1 table. So the light went on for me. From then on I've merged all 8 tables into one and if any of the subordinate table data isn't available for a row, its columns are set to NULL, which is the values they would have had anyway after a left join. I am perfectly happy know with one wide table with over 100 columns. Everything is in its place and maintenance is a dream. Queries are also quite fast because all of the information is under one table and not 8. I don't have to worry about optimizing the indexes for the table joins because there aren't any joins between these tables because it is all in 1 row. So you really have to ask yourself, why spend 10 minutes each time your query is run? Instead you eliminate the query altogether by keeping the data of the 2 tables into 1 table in the first place. Mike At 09:45 AM 9/6/2009, Jia Chen wrote: Thanks for your reply, Mike. Yes, 13419851 rows were added to rmpdata1. However, 10 minutes seem to be too long. I run the same join by using SQL procedure in a statistical software called SAS on a similar machine. It only takes 1 minute and 3 seconds. Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. Could you elaborate that? I was using B-tree index. Switching to HASH does help. Now, it takes 4 min 50.17 sec to run the query. I also turn on profiling by using mysql set profiling = 1; Query OK, 0 rows affected (0.01 sec) After the query finishes, I get mysql show profile; +--++ | Status | Duration | +--++ | starting | 0.000123 | | checking permissions | 0.10 | | Opening tables | 0.44 | | System lock | 0.07 | | Table lock | 0.11
Re: How to optimize a slow query?
Jia, The code you sent seems to be able to get the job done. You could try something simpler by executing 2 sql statements instead of using one. Something like: create table rmpdata1 select ri.*, mv.* from RItime as ri left join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)); insert into rmpdata1 select ri.*, mv.* from MVtime as mv left join RItime as ri on (ri.code=mv.code and ri.ndate=mv.ndate)) where ri.code is null and ri.date is null; You will of course have to play with the column list to avoid duplicate columns. The Insert statement will insert rows from mv that are missing in ri. Mike At 01:51 PM 9/6/2009, Jia Chen wrote: Hi Mike, Thanks for your detailed answer. Now, I understand what you mean. And, yes, I agree with you that keeping all data in one table works better for a bunch of 1:1 relationship tables. Actually, this is what I was trying to do with that query. Since you mention They all had a 1:1 relationship and occasionally some of the tables did not have a corresponding row. and From then on I've merged all 8 tables into one and if any of the subordinate table data isn't available for a row, its columns are set to NULL, I do want to ask you about how you set the columns to NULL for rows in subordinate table data unavailable because I have similar situation. If I want to combine two tables into one, I think that a full outer join can achieve what you did. However, MySQL does not have full outer join. So, I am using create table rmpdata1 (select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri left outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)) union (select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri right outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate)); This query takes more than twice as much time as the query in my first e-mail. Do you have a better way? Thanks. Best, Jia mos wrote: Jia, Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. Could you elaborate that? Sure but first I have to relate it to my own experience. I had 8 tables of around 25 million rows each. They all had a 1:1 relationship and occasionally some of the tables did not have a corresponding row. I felt it was better from a design point of view to have 8 different tables and do the joins on the tables that I needed for each of my particular queries. I'd be joining anywhere from 2 to 5 or 6 or even all 8 tables at a time, using a where clause to select 15k rows at a time. This is the way to do it from a normalized point of view. All of the information is in its respective table and only assemble the tables for each particular query. Well, this was slwww! A heck of a lot of work was done to join the tables together on a 2 column key (like yours). I also had to run maintenance on the tables to see which tables where corrupted or were missing rows that should have been there. The tables also repeated columns from the other tables like date and product_id that is used to help identify each row. Well to make a long story short, it was far too much effort to juggle the relationships between all of these tables. Then a colleague made the monumental announcement by saying I've never found the need to use more than 1 table when there was a 1:1 relationship. There is a tremendous speed cost involved in piecing the data back together. I put all of the data into 1 table. So the light went on for me. From then on I've merged all 8 tables into one and if any of the subordinate table data isn't available for a row, its columns are set to NULL, which is the values they would have had anyway after a left join. I am perfectly happy know with one wide table with over 100 columns. Everything is in its place and maintenance is a dream. Queries are also quite fast because all of the information is under one table and not 8. I don't have to worry about optimizing the indexes for the table joins because there aren't any joins between these tables because it is all in 1 row. So you really have to ask yourself, why spend 10 minutes each time your query is run? Instead you eliminate the query altogether by keeping the data of the 2 tables into 1 table in the first place. Mike At 09:45 AM 9/6/2009, Jia Chen wrote: Thanks for your reply, Mike. Yes, 13419851 rows were added to rmpdata1. However, 10 minutes seem to be too long. I run the same join by using SQL procedure in a statistical software called SAS on a similar machine. It only takes 1 minute and 3 seconds. Yes, it is a 1:1 relationship between table RItime and MVtime. However, I don't get your suggestion, I'd recommend
How to optimize a slow query?
Hi there, One simple query took more than 10 minutes. Here is how relevant rows in the slow query log looks like: # Time: 090905 10:49:57 # u...@host: root[root] @ localhost [] # Query_time: 649 Lock_time: 0 Rows_sent: 0 Rows_examined: 26758561 use world; create table rmpdata1 select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri left outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate); When I explain only the select clause, I get +--+---+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | ++-+---++---+-+-+--+--+---+ | 1 | SIMPLE | ri| ALL| NULL | NULL| NULL | NULL | 13419851 | | | 1 | SIMPLE | mv| eq_ref | PRIMARY | PRIMARY | 11 | world.ri.code,world.ri.ndate |1 | | ++-+---++---+-+-+--+--+---+ 2 rows in set (0.00 sec) I use show table status from world; to get information about two tables, RItime and MVtime, in the join clause: Name: RItime Engine: MyISAM Version: 10 Row_format: Dynamic Rows: 13419851 Avg_row_length: 31 Data_length: 427721848 Max_data_length: 281474976710655 Index_length: 347497472 Data_free: 0 Auto_increment: NULL Create_time: 2009-09-03 10:17:57 Update_time: 2009-09-03 12:04:02 Check_time: NULL Collation: latin1_swedish_ci Checksum: NULL Create_options: Comment: *** 2. row *** Name: MVtime Engine: MyISAM Version: 10 Row_format: Dynamic Rows: 13562373 Avg_row_length: 31 Data_length: 430220056 Max_data_length: 281474976710655 Index_length: 350996480 Data_free: 0 Auto_increment: NULL Create_time: 2009-09-03 13:31:33 Update_time: 2009-09-03 13:43:51 Check_time: NULL Collation: latin1_swedish_ci Checksum: NULL Create_options: Comment: I also describe these two tables: mysql desc RItime; +---++--+-++---+ | Field | Type | Null | Key | Default| Extra | +---++--+-++---+ | code | varchar(6) | NO | PRI || | | ndate | date | NO | PRI | -00-00 | | | ri| double | YES | | NULL | | | time | date | YES | | NULL | | | bdate | date | YES | | NULL | | +---++--+-++---+ 5 rows in set (0.00 sec) mysql desc MVtime; +---++--+-++---+ | Field | Type | Null | Key | Default| Extra | +---++--+-++---+ | code | varchar(6) | NO | PRI || | | ndate | date | NO | PRI | -00-00 | | | MV| double | YES | | NULL | | | time | date | YES | | NULL | | | bdate | date | YES | | NULL | | +---++--+-++---+ 5 rows in set (0.00 sec) Could you give me some hint on how to improve the speed of this query? Thanks. Best, Jia -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql?unsub=arch...@jab.org
Re: How to optimize a slow query?
How many rows were added to rmpdata1 table? If it is 13.4 million rows then it is going to take several minutes to join this many rows from the 2 tables. Is there a 1:1 relationship between the two tables or a 1:Many? If there is a 1:1 then I'd recommend joining the two tables into 1 table so you don't have to join them in the first place. The only other thing I can suggest is to change the type of index on the tables being joined to see if that makes a speed difference. For example, if you are using BTREE then switch to HASH or vice versa. See http://dev.mysql.com/doc/refman/5.0/en/create-index.html for more info. Mike At 10:05 AM 9/5/2009, Jia Chen wrote: Hi there, One simple query took more than 10 minutes. Here is how relevant rows in the slow query log looks like: # Time: 090905 10:49:57 # u...@host: root[root] @ localhost [] # Query_time: 649 Lock_time: 0 Rows_sent: 0 Rows_examined: 26758561 use world; create table rmpdata1 select ri.*, mv.MV, coalesce(ri.code,mv.code) as ccode, coalesce(ri.ndate,mv.ndate) as cndate from RItime as ri left outer join MVtime as mv on (ri.code=mv.code and ri.ndate=mv.ndate); When I explain only the select clause, I get +--+---+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | ++-+---++---+-+-+--+--+---+ | 1 | SIMPLE | ri| ALL| NULL | NULL| NULL | NULL | 13419851 | | | 1 | SIMPLE | mv| eq_ref | PRIMARY | PRIMARY | 11 | world.ri.code,world.ri.ndate |1 | | ++-+---++---+-+-+--+--+---+ 2 rows in set (0.00 sec) I use show table status from world; to get information about two tables, RItime and MVtime, in the join clause: Name: RItime Engine: MyISAM Version: 10 Row_format: Dynamic Rows: 13419851 Avg_row_length: 31 Data_length: 427721848 Max_data_length: 281474976710655 Index_length: 347497472 Data_free: 0 Auto_increment: NULL Create_time: 2009-09-03 10:17:57 Update_time: 2009-09-03 12:04:02 Check_time: NULL Collation: latin1_swedish_ci Checksum: NULL Create_options: Comment: *** 2. row *** Name: MVtime Engine: MyISAM Version: 10 Row_format: Dynamic Rows: 13562373 Avg_row_length: 31 Data_length: 430220056 Max_data_length: 281474976710655 Index_length: 350996480 Data_free: 0 Auto_increment: NULL Create_time: 2009-09-03 13:31:33 Update_time: 2009-09-03 13:43:51 Check_time: NULL Collation: latin1_swedish_ci Checksum: NULL Create_options: Comment: I also describe these two tables: mysql desc RItime; +---++--+-++---+ | Field | Type | Null | Key | Default| Extra | +---++--+-++---+ | code | varchar(6) | NO | PRI || | | ndate | date | NO | PRI | -00-00 | | | ri| double | YES | | NULL | | | time | date | YES | | NULL | | | bdate | date | YES | | NULL | | +---++--+-++---+ 5 rows in set (0.00 sec) mysql desc MVtime; +---++--+-++---+ | Field | Type | Null | Key | Default| Extra | +---++--+-++---+ | code | varchar(6) | NO | PRI || | | ndate | date | NO | PRI | -00-00 | | | MV| double | YES | | NULL | | | time | date | YES | | NULL | | | bdate | date | YES | | NULL | | +---++--+-++---+ 5 rows in set (0.00 sec) Could you give me some hint on how to improve the speed of this query? Thanks. Best, Jia -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql?unsub=mo...@fastmail.fm -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql?unsub=arch...@jab.org
