SQLite为什么不使用我的索引进行排序

Question

My Query:

SELECT *
FROM t1, t2
WHERE (t1.ZID=t2.ZCHARACTERID AND t1.ZID IN (1,2,3,4) AND t2.Z_ENT=3)
ORDER BY t2.ZSTROKECOUNT

My Indices:

CREATE INDEX i1 on t1(ZID);
CREATE INDEX i2 on t2(ZCHARACTERID, Z_ENT, ZSTROKECOUNT);

Explain Query Plan

selectid    order       from        detail                                                                         
----------  ----------  ----------  -----------------------------------------------------------------  --------------
0           0           1           SEARCH TABLE t1 USING INDEX i1 (ZID=?) (~740 rows)
0           0           0           EXECUTE LIST SUBQUERY 1                                                        
0           1           0           SEARCH TABLE t2 USING INDEX i2 (ZCHARACTERID=? AND Z_ENT=?) (~9 row)
0           0           0           USE TEMP B-TREE FOR ORDER BY    

From line 3 of the explain query plan, it says only two indexed columns are used and temp b-tree is used for order by. But from what I understand, I should be able to use i2 for order by as well.

Did I miss anything? Thanks.

Answer 1

because you forgot FROM clause

try this way

   SELECT * FROM your_table WHERE (t1.ZID=t2.ZCHARACTERID AND t1.ZID IN (1,2,3,4) AND t2.Z_ENT=3) ORDER BY t2.ZSTROKECOUNT

Answer 2

The index is not ordered by ZSTROKECOUNT .

SQLite will use the index for sorting if you do this:

DROP INDEX i2;
CREATE INDEX i3 ON t2(ZSTROKECOUNT, ZCHARACTERID, Z_ENT);