Hello all,
I am trying to write a utility that processes the results of EXPLAIN QUERY
PLAN statements and presents them in a graphical manner to developers. I
need to extract information from the "detail" column of the returned result
set (e.g. table name, index name, estimated rows etc.) and since the detail
is somewhat verbose I decided to write a small parser to parse it. After
some examination I have come up with the following EBNF:
plan_statement :=
( scan |
search |
aggregate |
compound |
execute |
use )
scan ::=
"SCAN" ( "TABLE" ObjectName | "SUBQUERY" int ) ["AS" identifier] [ using
] [ cost ]
search ::=
"SEARCH" ( "TABLE" ObjectName | "SUBQUERY" int) ["AS" identifier] [ using
] [ filter_expr ] [ cost ]
aggregate ::=
"USE TEMP B-TREE FOR" aggregate_operation
compound ::=
"COMPOUND SUBQUERIES" int "AND" int SET_OPERATION
execute ::=
"EXECUTE" ("LIST" | "CORRELATED SCALAR") "SUBQUERY" int
using ::=
"USING" (
"AUTOMATIC" ["COVERING"] "INDEX" |
["COVERING"] "INDEX" ObjectName |
"INTEGER PRIMARY KEY"
)
cost ::=
"(~" int "rows)"
aggregate_operation ::=
("GROUP BY" | "ORDER BY")
filter_expr ::=
"(" ColumnName "=" "?" ["AND" ColumnName "=" "?"]* ")"
set_operation ::= ( "UNION" ["ALL"] | "INTERSECT" | "MINUS" | "EXCEPT" )
use ::=
"USE" ["TEMP"] "B-TREE" FOR ( "GROUP BY" | "ORDER BY" )
ColumnName ::=
identifier
ObjectName ::=
identifier
where sequences are separated by spaces, literals are quoted, production
names are unquoted idents, ( ... | ... ) denote choice groups and [ ... ]
denote optional sequences. Productions "identifier" and "int" are omitted
as trivial.
So far this grammar covers plans of all statements I have examined. Could
someone (probably an SQLite developer) tell me if this grammar covers all
cases of "detail" values or if there are cases I have missed? Maybe the
NGQP has introduced some changes I have missed?
Also, regarding object names, do they include database names if
tables/indexes from attached databases are used in the query? (ObjectName
::= [ identifier '.' ] identifier instead of ObjectName ::= identifier)
Thank you in advance.
--
Constantine
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