Do Parallel Inserts And Selects Slow Down A Query?
I've been facing problems with a query which I think is relatively well optimized but has been performing really slow as of late as the size of the table has increased to more than 1GB. The MyISAM table is updated every few seconds, only a few rows, and a different set of rows are selected every few seconds.Wwould that cause a slowdown and if so, what is the solution?
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Nested SELECTS And SUM()
trying to calculate the amount owed by a customer: SELECT c.compdirectdebit_number, SUM( ( cr.cramount + cr.crvat ) - ( SELECT SUM( cppaid ) AS paid FROM companypaid cp WHERE c.compcompanyid=cp.cpcompanyid) ) AS debit FROM company c, companyreminder cr WHERE c.compcompanyid = cr.crcompanyid GROUP BY c.compcompanyid I want to sum the amount+vat and then - the SUM of the payments which should give us the amount owed. The nested select though is obvioulsy wong, but since this is the second time Ive used them, im struggling with the syntax.
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Pattern Selects
I have a few columns with strings stored in base64 and need to do patterned searches within those strings. Is there any built in base64 encoders/decoders that would allow selects something like the following? select id, name from files where base64Decode(name) like '%bob%' or conversely something like this select id, name from files where name like '%base64Encode(bob)%'
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Selects With If-thens
I want to do a query where I get the records after a date, the date is the last date in a table, if that table is empty then the date is the start of another Something like: select * from log1 where timestamp > isnull(select timestamp from log2 order by timestamp desc limit 1, select timestamp from log3 order by timestamp asc limit 1) I have tried all sorts of things like local variabless and so on, but it is not playing. The code has to be ansi sql too, or at least run on most databases.
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Doing 2 Selects In One Statement Possible?
How can I do 2 selects in one Sql statement. What I'm trying to do is below. So instead of using two statements can i do this in one? I'm using the same table from my last query. select t_stamp as a from day_count where c_col = '6' join select t_stamp as b from day_count where c_col = '1' "6" "2007-11-08 01:01:10" "5" "2007-11-11 01:01:10" "0" "2007-12-08 01:01:10" "1" "2007-12-09 01:01:10" "2" "2007-12-10 01:01:10" "3" "2007-12-11 01:01:10" "4" "2007-12-12 01:01:10" But nothing works.
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Nested SELECTS?
SELECT PPosts.* , (SELECT Count(ID) FROM PComments WHERE PComments.ForPostID = PPosts.ID) AS CommentCounts FROM PPosts Well is this possible in MySQL 4? ? ?? Cos i've developed my site in MySQL5 and it worked fine with this, but when i put on the hosting server which is MySQL4 i get this message: #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 Count(ID) FROM PComments WHERE PComments.ForPostID = PPo
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Performance When Using Sub-selects
i'm using a mysql select that has a sub select in it, something like this: Code: SELECT *, (SELECT * FROM other_table) AS other_column FROM my_table; i've never needed to do anything like this before so i'm a little curious about performance. do queries like this cause a significant performance?
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Wildcard Vs Defined Selects
At which point is it better to do a wildcard select compared to defined as per below, or is it better in all cases to do a wildcard or defined? Is there a speed difference? This is for use within php scripts and not via command line type selects. wildcard- SELECT t.*, ................from $threads t........... defined- SELECT t.field1, t.field2, t.field3, t.field4 ................from $threads t........... Also... SELECT t.*,f.name FROM $threads t, $forums f WHERE t.fid=f.fid is this better being done with a join and which mysql version started supporting joins?
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Multiple Selects Efficiency
Someone could help get a better understanding of the mechanics of this language. For example, I have two tables: one called 'articles' and other called 'autors'. What I want is to select all the columns from the 'articles' table, based on the article name, and then select all the columns from the 'autors' table, based on the autor of that article. So I came up with the following php code: $article_name = $_POST['article']; $query = "SELECT * FROM articles WHERE title='".$article_name."'"; $result = mysql_query($query); if($result){ while($row = mysql_fetch_array($result)){ $search_autor = $row['autor']; } $query_autor = "SELECT * FROM autors WHERE name='".$search_autor."'"; $result_autor = mysql_query($query_autor); if($result_autor){ //echoes out all the results } } It works, but I'm worried about its efficiency, because after all it's two querys. Is there a way to, with just one single query statement, do it all? Also, could you point me to some article or site that talks about the different query statements?
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Case Sensitivity In Selects
Is there a function where i can set a search criteria to be case insensitive? eg: select img_id, img_title from images where img_filename LIKE setCase(Insensitive, '%portugal%'); The filenames that are stored in the need to be case sensitive for file referencing, so i need to be able to match files & folder names like Portugal, portuGal, PORTUGAL etc etc. Any ideas people might have?
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