Let's take this example explain select * from employee,company,location where location.name= company.name and location.name=employee.name;
addr opcode p1 p2 p3 p4 p5 comment ---- ------------- ---- ---- ---- ------------- -- ------------- 0 Init 0 46 0 00 Start at 46 1 OpenRead 0 2 0 2 00 root=2 iDb=0; employee 2 OpenRead 2 3 0 2 00 root=3 iDb=0; location 3 OpenRead 1 4 0 2 00 root=4 iDb=0; company 4 Explain 0 0 0 SCAN TABLE employee 00 5 Rewind 0 44 0 00 6 Once 0 15 0 00 7 OpenAutoindex 3 3 0 k(3,nil,nil,nil) 00 nColumn=3; for location 8 Rewind 2 15 0 00 9 Column 2 0 2 00 r[2]= location.name 10 Column 2 1 3 00 r[3]=location.addr 11 Rowid 2 4 0 00 r[4]=rowid 12 MakeRecord 2 3 1 00 r[1]=mkrec(r[2..4]) 13 IdxInsert 3 1 0 10 key=r[1] 14 Next 2 9 0 03 15 Explain 0 1 2 SEARCH TABLE location USING AUTOMATIC COVERING INDEX (name=?) 00 16 Column 0 0 5 00 r[5]= employee.name 17 IsNull 5 43 0 00 if r[5]==NULL goto 43 18 SeekGE 3 43 5 1 00 key=r[5] 19 IdxGT 3 43 5 1 00 key=r[5] 20 Once 1 29 0 00 21 OpenAutoindex 4 3 0 k(3,nil,nil,nil) 00 nColumn=3; for company 22 Rewind 1 29 0 00 23 Column 1 0 2 00 r[2]= company.name 24 Column 1 1 3 00 r[3]=company.cname 25 Rowid 1 4 0 00 r[4]=rowid 26 MakeRecord 2 3 1 00 r[1]=mkrec(r[2..4]) 27 IdxInsert 4 1 0 10 key=r[1] 28 Next 1 23 0 03 29 Explain 0 2 1 SEARCH TABLE company USING AUTOMATIC COVERING INDEX (name=?) 00 30 Column 3 0 6 00 r[6]= location.name 31 IsNull 6 42 0 00 if r[6]==NULL goto 42 32 SeekGE 4 42 6 1 00 key=r[6] 33 IdxGT 4 42 6 1 00 key=r[6] 34 Copy 5 7 0 00 r[7]=r[5] 35 Column 0 1 8 00 r[8]=employee.age 36 Column 4 0 9 00 r[9]= company.name 37 Column 4 1 10 00 r[10]=company.cname 38 Copy 6 11 0 00 r[11]=r[6] 39 Column 3 1 12 00 r[12]=location.addr 40 ResultRow 7 6 0 00 output=r[7..12] 41 Next 4 33 0 00 42 Next 3 19 0 00 43 Next 0 6 0 01 44 Close 0 0 0 00 45 Halt 0 0 0 00 46 Transaction 0 0 3 0 01 47 TableLock 0 2 0 employee 00 iDb=0 root=2 write=0 48 TableLock 0 3 0 location 00 iDb=0 root=3 write=0 49 TableLock 0 4 0 company 00 iDb=0 root=4 write=0 50 Goto 0 1 0 00 How's the register for the highlighted opcode allocated and how does the virtual machine remember this allocation ? Thanks for your help On Fri, Sep 19, 2014 at 9:46 AM, Richard Hipp <d...@sqlite.org> wrote: > On Fri, Sep 19, 2014 at 12:10 AM, Prakash Premkumar < > prakash.p...@gmail.com> > wrote: > > > Thanks for your reply. I would like to know how the register allocation > > decision is made and the part of the code which does it . can you please > > help me find that? Thanks > > > > Which register. > > Show me a specific VDBE program and a specific instruction in that program > and a specific operand on that instruction, and I can point you to the > place in the code where that register is allocated. > > > -- > D. Richard Hipp > d...@sqlite.org > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
