我在 sqlite3 db 中有位于内存映射分区上的表。我有如下查询计划的 select 语句:
sqlite3> EXPLAIN QUERY PLAN SELECT sst.prefix, 0 AS pb, sst.rate,
sst.rate_n, sst.interval_1, sst.interval_n
FROM sch AS sst
WHERE
sst.i_workbook_id = 989 AND
sst.prefix IN ('', '1', '19', '191', '1919', '19198') AND
sst.activation_date <= DATETIME('now') AND
(sst.expiration_date > DATETIME('now') OR sst.expiration_date IS NULL) AND
sst.start_time <= TIME('now') AND
sst.end_time >= TIME('now');
0|0|0|SCAN TABLE sch AS sst (~185 rows)
0|0|0|EXECUTE LIST SUBQUERY 1
现在,如果我添加订单,那么他的查询计划会两次命中主表,并且比以前长 4 倍,而表有 130 万行但过滤的行只有两个。
这是新的查询计划:
sqlite3> EXPLAIN QUERY PLAN SELECT sst.prefix, 0 AS pb, sst.rate,
sst.rate_n, sst.interval_1, sst.interval_n
FROM sch AS sst
WHERE
sst.i_workbook_id = 989 AND
sst.prefix IN ('', '1', '19', '191', '1919', '19198') AND
sst.activation_date <= DATETIME('now') AND
(sst.expiration_date > DATETIME('now') OR sst.expiration_date IS NULL) AND
sst.start_time <= TIME('now') AND
sst.end_time >= TIME('now') order by sst.prefix;
0|0|0|EXECUTE LIST SUBQUERY 1
0|0|0|SEARCH TABLE sch AS sst USING AUTOMATIC COVERING INDEX (i_workbook_id=?) (~7 rows)
0|0|0|EXECUTE LIST SUBQUERY 1
0|0|0|SEARCH TABLE sch AS sst USING AUTOMATIC COVERING INDEX (i_workbook_id=?) (~7 rows)
0|0|0|EXECUTE LIST SUBQUERY 1
0|0|0|USE TEMP B-TREE FOR ORDER BY
有任何想法吗?我究竟做错了什么?