Query Too Complex
in [Queries]
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From: david on 6 Jul 2008 07:17 Queries are optimised all the way through the stack, so it is not 'more efficient' to put the selection at the bottom of the stack -- it just makes the query more complex to optimise for ODBC. The internal rules for optimisation of an ODBC query are arcane, unspecified and yes, different from the Jet optimisation, because the Jet engine does call-backs to get Date(), before getting the records from an MDB, but the ODBC version applies that selection criteria in Jet after getting all the records from ODBC first. In any case, just re-write the query stack so that it is different: any change changes the optimiser path, and so can change if it considers the query too complex. (david) "cpsaltis" <cpsaltis(a)discussions.microsoft.com> wrote in message news:E75F9161-C2BF-419C-ACA2-D746ECCBBD2A(a)microsoft.com... > > > "louisjohnphillips(a)gmail.com" wrote: > > > On Jul 4, 10:41 am, cpsaltis <cpsal...(a)discussions.microsoft.com> > > wrote: > > > I have nested queries that when run on a local table runs correctly. When I > > > switch the first query to use ODBC tables I get query too complex. If I run > > > the individual queries (in the nest) they work all the way to the very last > > > one (that the report uses). Other than the ODBC connection the difference is > > > local table is single table, ODBC is two linked tables. I've see here that > > > there is a 64k compiled limit to the size of the query. Is there a way to > > > identify the size? Is there a different limit when using and ODBC connection? > > > > > > Thanks in advance > > > > Can it be assumed that the ODBC connection is to a database that > > supports views? View seen by Access through an ODBC connection appear > > if they are tables. > > > > Rather than worry about the limit of the size of a query, try breaking > > the query into views that have performed most of the selection work. > > Use this technic to simplify the complex query. > > > > I don't quite understand your comments about views. > > The reason for nesting, other than some calculations etc, is to limit > selections. The first 4 do most of the selction work. I've included the 2nd & > 4th for example. The reason they are in different queries is to simplify. > > SELECT [qAR-1].* > FROM [qAR-1] > WHERE ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > (([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date]))) OR > ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > (([Forms]![fARSelections]![MonthNum]) Is Null)) OR > ((([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])) AND > (([Forms]![fARSelections]![BranchNum]) Is Null)) OR > ((([Forms]![fARSelections]![MonthNum]) Is Null) AND > (([Forms]![fARSelections]![BranchNum]) Is Null)); > > SELECT [qAR-3].* > FROM [qAR-3] > WHERE ((([Forms]![fARSelections]![CustType])=0 Or > ([Forms]![fARSelections]![CustType])=-1)) OR > ((([Forms]![fARSelections]![CustType])=1) AND > (([qAR-3].cu_install)>(Date()-365))) OR > ((([Forms]![fARSelections]![CustType])=2) AND > (([qAR-3].cu_install)<=(Date()-365))); >
From: cpsaltis on 6 Jul 2008 13:19 David, Thank you for the explanation. I also ran across a post from Michel Walsh demonstrating an alternative to the criteria [field] with separate line for [field] is null which gets complicated with multiple fields, ie ([field1] AND [field2]) OR ([field1] AND [field2] is null) OR ([field1] is null AND [field2]) OR ([field1] if null AND [field2] is null) which allowed me to also reduce the number of sub queries. Queries now work with ODBC link. SELECT [qAR-1].* FROM [qAR-1] WHERE (((IIf(([Forms]![fARSelections]![BranchNum]) Is Null,True,([cu_branch])=[Forms]![fARSelections]![BranchNum]))<>False) AND ((IIf(([Forms]![fARSelections]![MonthNum]) Is Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>False) AND (([Forms]![fARSelections]![CustType])=0 Or ([Forms]![fARSelections]![CustType])=-1)) OR (((IIf(([Forms]![fARSelections]![BranchNum]) Is Null,True,([cu_branch]=[Forms]![fARSelections]![BranchNum]))<>False) AND ((IIf(([Forms]![fARSelections]![MonthNum]) Is Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>False) AND (([Forms]![fARSelections]![CustType])=1) AND ([cu_install]>(Date()-365))) OR (((IIf(([Forms]![fARSelections]![BranchNum]) Is Null,True,([cu_branch]=[Forms]![fARSelections]![BranchNum]))<>False) AND ((IIf(([Forms]![fARSelections]![MonthNum]) Is Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>False) AND (([Forms]![fARSelections]![CustType])=2) AND ([cu_install]<=(Date()-365))); "david(a)epsomdotcomdotau" wrote: > Queries are optimised all the way through the stack, > so it is not 'more efficient' to put the selection at the > bottom of the stack -- it just makes the query more > complex to optimise for ODBC. > > The internal rules for optimisation of an ODBC query > are arcane, unspecified and yes, different from the Jet > optimisation, because the Jet engine does call-backs > to get Date(), before getting the records from an MDB, > but the ODBC version applies that selection criteria in > Jet after getting all the records from ODBC first. > > In any case, just re-write the query stack so that it is > different: any change changes the optimiser path, and > so can change if it considers the query too complex. > > (david) > > > "cpsaltis" <cpsaltis(a)discussions.microsoft.com> wrote in message > news:E75F9161-C2BF-419C-ACA2-D746ECCBBD2A(a)microsoft.com... > > > > > > "louisjohnphillips(a)gmail.com" wrote: > > > > > On Jul 4, 10:41 am, cpsaltis <cpsal...(a)discussions.microsoft.com> > > > wrote: > > > > I have nested queries that when run on a local table runs correctly. > When I > > > > switch the first query to use ODBC tables I get query too complex. If > I run > > > > the individual queries (in the nest) they work all the way to the very > last > > > > one (that the report uses). Other than the ODBC connection the > difference is > > > > local table is single table, ODBC is two linked tables. I've see here > that > > > > there is a 64k compiled limit to the size of the query. Is there a way > to > > > > identify the size? Is there a different limit when using and ODBC > connection? > > > > > > > > Thanks in advance > > > > > > Can it be assumed that the ODBC connection is to a database that > > > supports views? View seen by Access through an ODBC connection appear > > > if they are tables. > > > > > > Rather than worry about the limit of the size of a query, try breaking > > > the query into views that have performed most of the selection work. > > > Use this technic to simplify the complex query. > > > > > > > I don't quite understand your comments about views. > > > > The reason for nesting, other than some calculations etc, is to limit > > selections. The first 4 do most of the selction work. I've included the > 2nd & > > 4th for example. The reason they are in different queries is to simplify. > > > > SELECT [qAR-1].* > > FROM [qAR-1] > > WHERE ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > > (([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date]))) OR > > ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > > (([Forms]![fARSelections]![MonthNum]) Is Null)) OR > > ((([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])) AND > > (([Forms]![fARSelections]![BranchNum]) Is Null)) OR > > ((([Forms]![fARSelections]![MonthNum]) Is Null) AND > > (([Forms]![fARSelections]![BranchNum]) Is Null)); > > > > SELECT [qAR-3].* > > FROM [qAR-3] > > WHERE ((([Forms]![fARSelections]![CustType])=0 Or > > ([Forms]![fARSelections]![CustType])=-1)) OR > > ((([Forms]![fARSelections]![CustType])=1) AND > > (([qAR-3].cu_install)>(Date()-365))) OR > > ((([Forms]![fARSelections]![CustType])=2) AND > > (([qAR-3].cu_install)<=(Date()-365))); > > > > >
From: cpsaltis on 6 Jul 2008 13:26 Opps, should have said separate line in Design View. "cpsaltis" wrote: > David, > > Thank you for the explanation. > > I also ran across a post from Michel Walsh demonstrating an alternative to > the criteria [field] with separate line for [field] is null which gets > complicated with multiple fields, ie ([field1] AND [field2]) OR ([field1] AND > [field2] is null) OR ([field1] is null AND [field2]) OR ([field1] if null AND > [field2] is null) which allowed me to also reduce the number of sub queries. > Queries now work with ODBC link. > > SELECT [qAR-1].* > FROM [qAR-1] > WHERE (((IIf(([Forms]![fARSelections]![BranchNum]) Is > Null,True,([cu_branch])=[Forms]![fARSelections]![BranchNum]))<>False) AND > ((IIf(([Forms]![fARSelections]![MonthNum]) Is > Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>False) > AND (([Forms]![fARSelections]![CustType])=0 Or > ([Forms]![fARSelections]![CustType])=-1)) OR > (((IIf(([Forms]![fARSelections]![BranchNum]) Is > Null,True,([cu_branch]=[Forms]![fARSelections]![BranchNum]))<>False) AND > ((IIf(([Forms]![fARSelections]![MonthNum]) Is > Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>False) > AND (([Forms]![fARSelections]![CustType])=1) AND ([cu_install]>(Date()-365))) > OR (((IIf(([Forms]![fARSelections]![BranchNum]) Is > Null,True,([cu_branch]=[Forms]![fARSelections]![BranchNum]))<>False) AND > ((IIf(([Forms]![fARSelections]![MonthNum]) Is > Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>False) > AND (([Forms]![fARSelections]![CustType])=2) AND > ([cu_install]<=(Date()-365))); > > > "david(a)epsomdotcomdotau" wrote: > > > Queries are optimised all the way through the stack, > > so it is not 'more efficient' to put the selection at the > > bottom of the stack -- it just makes the query more > > complex to optimise for ODBC. > > > > The internal rules for optimisation of an ODBC query > > are arcane, unspecified and yes, different from the Jet > > optimisation, because the Jet engine does call-backs > > to get Date(), before getting the records from an MDB, > > but the ODBC version applies that selection criteria in > > Jet after getting all the records from ODBC first. > > > > In any case, just re-write the query stack so that it is > > different: any change changes the optimiser path, and > > so can change if it considers the query too complex. > > > > (david) > > > > > > "cpsaltis" <cpsaltis(a)discussions.microsoft.com> wrote in message > > news:E75F9161-C2BF-419C-ACA2-D746ECCBBD2A(a)microsoft.com... > > > > > > > > > "louisjohnphillips(a)gmail.com" wrote: > > > > > > > On Jul 4, 10:41 am, cpsaltis <cpsal...(a)discussions.microsoft.com> > > > > wrote: > > > > > I have nested queries that when run on a local table runs correctly. > > When I > > > > > switch the first query to use ODBC tables I get query too complex. If > > I run > > > > > the individual queries (in the nest) they work all the way to the very > > last > > > > > one (that the report uses). Other than the ODBC connection the > > difference is > > > > > local table is single table, ODBC is two linked tables. I've see here > > that > > > > > there is a 64k compiled limit to the size of the query. Is there a way > > to > > > > > identify the size? Is there a different limit when using and ODBC > > connection? > > > > > > > > > > Thanks in advance > > > > > > > > Can it be assumed that the ODBC connection is to a database that > > > > supports views? View seen by Access through an ODBC connection appear > > > > if they are tables. > > > > > > > > Rather than worry about the limit of the size of a query, try breaking > > > > the query into views that have performed most of the selection work. > > > > Use this technic to simplify the complex query. > > > > > > > > > > I don't quite understand your comments about views. > > > > > > The reason for nesting, other than some calculations etc, is to limit > > > selections. The first 4 do most of the selction work. I've included the > > 2nd & > > > 4th for example. The reason they are in different queries is to simplify. > > > > > > SELECT [qAR-1].* > > > FROM [qAR-1] > > > WHERE ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > > > (([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date]))) OR > > > ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > > > (([Forms]![fARSelections]![MonthNum]) Is Null)) OR > > > ((([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])) AND > > > (([Forms]![fARSelections]![BranchNum]) Is Null)) OR > > > ((([Forms]![fARSelections]![MonthNum]) Is Null) AND > > > (([Forms]![fARSelections]![BranchNum]) Is Null)); > > > > > > SELECT [qAR-3].* > > > FROM [qAR-3] > > > WHERE ((([Forms]![fARSelections]![CustType])=0 Or > > > ([Forms]![fARSelections]![CustType])=-1)) OR > > > ((([Forms]![fARSelections]![CustType])=1) AND > > > (([qAR-3].cu_install)>(Date()-365))) OR > > > ((([Forms]![fARSelections]![CustType])=2) AND > > > (([qAR-3].cu_install)<=(Date()-365))); > > > > > > > > >
From: david on 7 Jul 2008 18:37
Glad it works :~) By the way, another difference between ODBC and JET optimisation is that ODBC can only handle one Left or Right Join per query. If you want to actually make lots of Left and Right joins run faster with ODBC, you have to use a pass-through query. Inner Joins are sent off to the ODBC server, but due to a limitation in ODBC SQL any more Left or Right joins are simulated by Jet by joining up the separate records returned by ODBC. This is because Left and Right joins were something of a new feature when Access was introduced, not well supported by other SQL databases. But this is just a note about optimisation :~) Left and Right joins don't make your query 'too complex' -- that message normally relates to the way the criteria are applied, as you have found. regards (david) "cpsaltis" <cpsaltis(a)discussions.microsoft.com> wrote in message news:F1D7BED3-34F8-4F72-AFB4-C1D3113A7D37(a)microsoft.com... > > Opps, should have said separate line in Design View. > > "cpsaltis" wrote: > > > David, > > > > Thank you for the explanation. > > > > I also ran across a post from Michel Walsh demonstrating an alternative to > > the criteria [field] with separate line for [field] is null which gets > > complicated with multiple fields, ie ([field1] AND [field2]) OR ([field1] AND > > [field2] is null) OR ([field1] is null AND [field2]) OR ([field1] if null AND > > [field2] is null) which allowed me to also reduce the number of sub queries. > > Queries now work with ODBC link. > > > > SELECT [qAR-1].* > > FROM [qAR-1] > > WHERE (((IIf(([Forms]![fARSelections]![BranchNum]) Is > > Null,True,([cu_branch])=[Forms]![fARSelections]![BranchNum]))<>False) AND > > ((IIf(([Forms]![fARSelections]![MonthNum]) Is > > Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>Fa lse) > > AND (([Forms]![fARSelections]![CustType])=0 Or > > ([Forms]![fARSelections]![CustType])=-1)) OR > > (((IIf(([Forms]![fARSelections]![BranchNum]) Is > > Null,True,([cu_branch]=[Forms]![fARSelections]![BranchNum]))<>False) AND > > ((IIf(([Forms]![fARSelections]![MonthNum]) Is > > Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>Fa lse) > > AND (([Forms]![fARSelections]![CustType])=1) AND ([cu_install]>(Date()-365))) > > OR (((IIf(([Forms]![fARSelections]![BranchNum]) Is > > Null,True,([cu_branch]=[Forms]![fARSelections]![BranchNum]))<>False) AND > > ((IIf(([Forms]![fARSelections]![MonthNum]) Is > > Null,True,([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])))<>Fa lse) > > AND (([Forms]![fARSelections]![CustType])=2) AND > > ([cu_install]<=(Date()-365))); > > > > > > "david(a)epsomdotcomdotau" wrote: > > > > > Queries are optimised all the way through the stack, > > > so it is not 'more efficient' to put the selection at the > > > bottom of the stack -- it just makes the query more > > > complex to optimise for ODBC. > > > > > > The internal rules for optimisation of an ODBC query > > > are arcane, unspecified and yes, different from the Jet > > > optimisation, because the Jet engine does call-backs > > > to get Date(), before getting the records from an MDB, > > > but the ODBC version applies that selection criteria in > > > Jet after getting all the records from ODBC first. > > > > > > In any case, just re-write the query stack so that it is > > > different: any change changes the optimiser path, and > > > so can change if it considers the query too complex. > > > > > > (david) > > > > > > > > > "cpsaltis" <cpsaltis(a)discussions.microsoft.com> wrote in message > > > news:E75F9161-C2BF-419C-ACA2-D746ECCBBD2A(a)microsoft.com... > > > > > > > > > > > > "louisjohnphillips(a)gmail.com" wrote: > > > > > > > > > On Jul 4, 10:41 am, cpsaltis <cpsal...(a)discussions.microsoft.com> > > > > > wrote: > > > > > > I have nested queries that when run on a local table runs correctly. > > > When I > > > > > > switch the first query to use ODBC tables I get query too complex. If > > > I run > > > > > > the individual queries (in the nest) they work all the way to the very > > > last > > > > > > one (that the report uses). Other than the ODBC connection the > > > difference is > > > > > > local table is single table, ODBC is two linked tables. I've see here > > > that > > > > > > there is a 64k compiled limit to the size of the query. Is there a way > > > to > > > > > > identify the size? Is there a different limit when using and ODBC > > > connection? > > > > > > > > > > > > Thanks in advance > > > > > > > > > > Can it be assumed that the ODBC connection is to a database that > > > > > supports views? View seen by Access through an ODBC connection appear > > > > > if they are tables. > > > > > > > > > > Rather than worry about the limit of the size of a query, try breaking > > > > > the query into views that have performed most of the selection work. > > > > > Use this technic to simplify the complex query. > > > > > > > > > > > > > I don't quite understand your comments about views. > > > > > > > > The reason for nesting, other than some calculations etc, is to limit > > > > selections. The first 4 do most of the selction work. I've included the > > > 2nd & > > > > 4th for example. The reason they are in different queries is to simplify. > > > > > > > > SELECT [qAR-1].* > > > > FROM [qAR-1] > > > > WHERE ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > > > > (([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date]))) OR > > > > ((([qAR-1].cu_branch)=[Forms]![fARSelections]![BranchNum]) AND > > > > (([Forms]![fARSelections]![MonthNum]) Is Null)) OR > > > > ((([Forms]![fARSelections]![MonthNum])=DatePart("m",[ph_date])) AND > > > > (([Forms]![fARSelections]![BranchNum]) Is Null)) OR > > > > ((([Forms]![fARSelections]![MonthNum]) Is Null) AND > > > > (([Forms]![fARSelections]![BranchNum]) Is Null)); > > > > > > > > SELECT [qAR-3].* > > > > FROM [qAR-3] > > > > WHERE ((([Forms]![fARSelections]![CustType])=0 Or > > > > ([Forms]![fARSelections]![CustType])=-1)) OR > > > > ((([Forms]![fARSelections]![CustType])=1) AND > > > > (([qAR-3].cu_install)>(Date()-365))) OR > > > > ((([Forms]![fARSelections]![CustType])=2) AND > > > > (([qAR-3].cu_install)<=(Date()-365))); > > > > > > > > > > > > > |