sqlite> explain select * from tbl1 where a > 20;
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 10 0 00 Start at 10
1 OpenRead 0 2 0 2 00 root=2 iDb=0; tbl1
2 Rewind 0 9 0 00
3 Column 0 0 1 00 r[1]=tbl1.a
4 Le 2 8 1 (BINARY) 51 if r[1]<=r[2] goto 8
5 Column 0 0 3 00 r[3]=tbl1.a
6 Column 0 1 4 00 r[4]=tbl1.b
7 ResultRow 3 2 0 00 output=r[3..4]
8 Next 0 3 0 01
9 Halt 0 0 0 00
10 Transaction 0 0 1 0 01 usesStmtJournal=0
11 Integer 20 2 0 00 r[2]=20
12 Goto 0 1 0 00
read more here - https://www.sqlite.org/opcode.html#codes