Theory Of Subqueries For 4.1.7
While converting SQL statements for a database change, I discovered a
big performance hit in MYSQL with subqueries vices Sybase. I'm hoping
that someone might be able to help me understand why?
I have two tables USERS (2200 records) and JOB Decriptions (163
records). I wanted to retrieve all the job description not in the
USER table. (No Indexes on JOBDESC currently)
select JOBDESC from JOBS where JOBDESC not in ( select JOBDESC from
USERS where JOBDESC not NULL )
In Sybase the query returns in about .56 secs
In Mysql 4.1.7 query returns in about 8.78 secs
The funny thing is if I run the query like so
select JOBDESC from JOBS where JOBDESC not in ('President','Vice
President','Treasaur','Secretary')
returns in .03 secs.
Those four descriptions are returned by the inner select.
All select statements individually return in .03 secs.
I created indexes on both tables for JOBDESC and reduced the time to
..97 secs. I used explain command to help understand what is going on
hence the indexes, but why the difference in speed?
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I have a table with a list of books, their genres (type), and price. I have attached it as an image. I would like to select all books whose price is higher than all books of type HOR. Basically, I think that this means: find the book of type HOR that is the most expensive. Then, select all other books whose price is greater than that. In this example, the most expensive HOR book is 19.60. Therefore, I need to select all books with price > 19.60 and not of type HOR. I tried using a subquery like this: SELECT * FROM BOOK WHERE PRICE > (SELECT MAX(PRICE) FROM BOOK WHERE TYPE='HOR' GROUP BY TYPE) However, I get an error that says: Quote: #1064 - You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT MAX( PRICE ) WHERE TYPE = 'HOR' GROUP BY TYPE ) LIMIT I looked up that error in the mysql doc but it didn't have much info in there: Quote: Error: 1064 SQLSTATE: 42000 (ER_PARSE_ERROR) Message: %s near '%s' at line %d
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“Rewriting Subqueries As Joins For Earlier MySQL Version
In my portal I use MySQL version 4.1.7 where i can use subquerys but now i need to move my portal to server where is MySQL version 3.23.58. This SQL statement should convert to form where is NO subquerys and do it only ONE statement: select * from ajanvaraus where toimenpidetunnus in(select toimenpidetunnus from toimenpide where kategorianimi = (select distinct kategorianimi from toimenpide where toimenpidetunnus = $tp))"; I managed to convert inner subquery to form: select taulu2.toimenpidetunnus from toimenpide as taulu1, toimenpide as taulu2 where taulu1.toimenpidetunnus = $tp and taulu1.kategorianimi = taulu2.kategorianimi now i need to compine my last two querys togehter.
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