sqlite statement can be preceded by the keyword "explain" or by the phrase "explain query plan" used for describing the details of a table.
either modification causes the sqlite statement to behave as a query and to return information about how the sqlite statement would have operated if the explain keyword or phrase had been omitted.
the output from explain and explain query plan is intended for interactive analysis and troubleshooting only.
the details of the output format are subject to change from one release of sqlite to the next.
applications should not use explain or explain query plan since their exact behavior is variable and only partially documented.
syntax
syntax for explain is as follows −
explain [sqlite query]
syntax for explain query plan is as follows −
explain query plan [sqlite query]
example
consider company table with the following records −
id name age address salary ---------- ---------- ---------- ---------- ---------- 1 paul 32 california 20000.0 2 allen 25 texas 15000.0 3 teddy 23 norway 20000.0 4 mark 25 rich-mond 65000.0 5 david 27 texas 85000.0 6 kim 22 south-hall 45000.0 7 james 24 houston 10000.0
now, let us check the following sub-query with select statement −
sqlite> explain select * from company where salary >= 20000;
this will produce the following result.
addr opcode p1 p2 p3 ---------- ---------- ---------- ---------- ---------- 0 goto 0 19 1 integer 0 0 2 openread 0 8 3 setnumcolu 0 5 4 rewind 0 17 5 column 0 4 6 realaffini 0 0 7 integer 20000 0 8 lt 357 16 collseq(bi 9 rowid 0 0 10 column 0 1 11 column 0 2 12 column 0 3 13 column 0 4 14 realaffini 0 0 15 callback 5 0 16 next 0 5 17 close 0 0 18 halt 0 0 19 transactio 0 0 20 verifycook 0 38 21 goto 0 1 22 noop 0 0
now, let us check the following explain query plan with select statement −
sqlite> explain query plan select * from company where salary >= 20000; order from detail ---------- ---------- ------------- 0 0 table company