我正在运行以下选择查询：
SELECT "entry"."id" AS "entry_id",
"entry"."input" AS "entry_input",
"entry"."output" AS "entry_output",
"entry"."numOfWords" AS "entry_numOfWords",
"entry"."times_seen" AS "entry_times_seen",
"word_class"."value" AS "word_class_value",
"dominant_noun"."noun" AS "dominant_noun_noun",
"dominant_noun"."article" AS "dominant_noun_article",
"dominant_noun"."isPluaral" AS "dominant_noun_isPluaral",
"subject"."subjectIndex" AS "subject_subjectIndex",
"last_time_visited"."value" AS "last_time_visited_value"
FROM "entry" "entry"
LEFT JOIN "word_class" "word_class" ON "word_class"."entryId"="entry"."id"
LEFT JOIN "dominant_noun" "dominant_noun" ON "dominant_noun"."entryId"="entry"."id"
LEFT JOIN "subject_entries_entry" "subject_entry" ON "subject_entry"."entryId"="entry"."id"
LEFT JOIN "subject" "subject" ON "subject"."id"="subject_entry"."subjectId"
LEFT JOIN "last_time_visited" "last_time_visited" ON "last_time_visited"."entryId"="entry"."id"
WHERE "entry"."inputLang" = 31
AND ("entry"."input" like '% hilfe %' OR "entry"."input" like 'hilfe %' OR "entry"."input" like '% hilfe')
ORDER BY "word_class"."value" DESC, "entry"."numOfWords" ASC;
时间结果：
real 0m15.100s
user 0m14.072s
sys 0m1.024s
针对此数据库架构：
CREATE TABLE sqlite_sequence(name,seq);
CREATE TABLE IF NOT EXISTS "subject" ("id" integer PRIMARY KEY AUTOINCREMENT NOT NULL, "subjectIndex" tinyint NOT NULL);
CREATE TABLE IF NOT EXISTS "entry" ("id" integer PRIMARY KEY AUTOINCREMENT NOT NULL, "inputLang" tinyint NOT NULL, "outputLang" tinyint NOT NULL, "input"
varchar NOT NULL, "output" varchar NOT NULL, "numOfWords" tinyint NOT NULL, "times_seen" integer NOT NULL DEFAULT (0));
CREATE TABLE IF NOT EXISTS "abbr" ("id" integer PRIMARY KEY AUTOINCREMENT NOT NULL, "value" varchar NOT NULL, "entryId" integer, CONSTRAINT "REL_ca935aaf7
66cba1e7bfbe90275" UNIQUE ("entryId"), CONSTRAINT "FK_ca935aaf766cba1e7bfbe902757" FOREIGN KEY ("entryId") REFERENCES "entry" ("id"));
CREATE TABLE IF NOT EXISTS "word_class" ("id" integer PRIMARY KEY AUTOINCREMENT NOT NULL, "value" integer NOT NULL, "entryId" integer, CONSTRAINT "REL_941
45442deb2b2209bd943a787" UNIQUE ("entryId"), CONSTRAINT "FK_94145442deb2b2209bd943a7874" FOREIGN KEY ("entryId") REFERENCES "entry" ("id"));
CREATE TABLE IF NOT EXISTS "dominant_noun" ("id" integer PRIMARY KEY AUTOINCREMENT NOT NULL, "noun" varchar NOT NULL, "article" tinyint NOT NULL, "isPluar
al" boolean NOT NULL, "entryId" integer, CONSTRAINT "REL_f493eeedea653d8a89f595c82c" UNIQUE ("entryId"), CONSTRAINT "FK_f493eeedea653d8a89f595c82c4" FOREI
GN KEY ("entryId") REFERENCES "entry" ("id"));
CREATE TABLE IF NOT EXISTS "last_time_visited" ("id" integer PRIMARY KEY AUTOINCREMENT NOT NULL, "value" datetime NOT NULL DEFAULT (CURRENT_TIMESTAMP), "e
ntryId" integer, CONSTRAINT "REL_e631a6f55d59214f8e6aaa6447" UNIQUE ("entryId"), CONSTRAINT "FK_e631a6f55d59214f8e6aaa64478" FOREIGN KEY ("entryId") REFER
ENCES "entry" ("id"));
CREATE TABLE IF NOT EXISTS "subject_entries_entry" ("subjectId" integer NOT NULL, "entryId" integer NOT NULL, CONSTRAINT "FK_d2eaa7a84a7963ed94e472cef0b"FOREIGN KEY ("subjectId") REFERENCES "subject" ("id") ON DELETE CASCADE, CONSTRAINT "FK_5f940450dd4c681a9fecf0b14b2" FOREIGN KEY ("entryId") REFERENCES "entry" ("id") ON DELETE CASCADE, PRIMARY KEY ("subjectId", "entryId"));
CREATE INDEX "IDX_3091789786b922bee00bbb44b1" ON "entry" ("inputLang") ;
CREATE INDEX "IDX_36ab3550b9e3ef647d1230affc" ON "entry" ("outputLang") ;
CREATE INDEX "IDX_1b0f6266dffb9a7e6343e7faa4" ON "entry" ("input") ;
CREATE INDEX "IDX_a77c7936ea412ec1958007154a" ON "entry" ("numOfWords") ;
CREATE INDEX "IDX_b32699a03d36223ff9bad94ea6" ON "entry" ("times_seen") ;
解释结果：
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 109 0 00 Start at 109
1 SorterOpen 6 14 0 k(2,-B,B) 00
2 OpenRead 0 12 0 7 00 root=12 iDb=0; entry
3 OpenRead 1 2 0 3 00 root=2 iDb=0; word_class
4 OpenRead 7 3 0 k(2,,) 02 root=3 iDb=0; sqlite_autoindex_word_class_1
5 OpenRead 2 5 0 5 00 root=5 iDb=0; dominant_noun
6 OpenRead 8 6 0 k(2,,) 02 root=6 iDb=0; sqlite_autoindex_dominant_noun_1
7 OpenRead 3 10 0 2 00 root=10 iDb=0; subject_entries_entry
8 OpenRead 4 9 0 2 00 root=9 iDb=0; subject
9 OpenRead 5 7 0 3 00 root=7 iDb=0; last_time_visited
10 OpenRead 9 8 0 k(2,,) 02 root=8 iDb=0; sqlite_autoindex_last_time_visited_1
11 Rewind 0 92 0 00
12 Column 0 1 1 00 r[1]=entry.inputLang
13 Ne 2 91 1 (BINARY) 54 if r[1]!=r[2] goto 91
14 Column 0 3 4 00 r[4]=entry.input
15 Function0 1 3 1 like(2) 02 r[1]=func(r[3..4])
16 If 1 23 0 00
17 Column 0 3 6 00 r[6]=entry.input
18 Function0 1 5 1 like(2) 02 r[1]=func(r[5..6])
19 If 1 23 0 00
20 Column 0 3 8 00 r[8]=entry.input
21 Function0 1 7 1 like(2) 02 r[1]=func(r[7..8])
22 IfNot 1 91 1 00
23 Integer 0 9 0 00 r[9]=0; init LEFT JOIN no-match flag
24 Rowid 0 10 0 00 r[10]=rowid
25 SeekGE 7 87 10 1 00 key=r[10]
26 IdxGT 7 87 10 1 00 key=r[10]
27 DeferredSeek 7 0 1 00 Move 1 to 7.rowid if needed
28 Integer 1 9 0 00 r[9]=1; record LEFT JOIN hit
29 Integer 0 11 0 00 r[11]=0; init LEFT JOIN no-match flag
30 Rowid 0 12 0 00 r[12]=rowid
31 SeekGE 8 83 12 1 00 key=r[12]
32 IdxGT 8 83 12 1 00 key=r[12]
33 DeferredSeek 8 0 2 00 Move 2 to 8.rowid if needed
34 Integer 1 11 0 00 r[11]=1; record LEFT JOIN hit
35 Once 0 44 0 00
36 OpenAutoindex 10 3 0 k(3,B,,) 00 nColumn=3; for subject_entries_entry
37 Rewind 3 44 0 00
38 Column 3 1 13 00 r[13]=subject_entries_entry.entryId
39 Column 3 0 14 00 r[14]=subject_entries_entry.subjectId
40 Rowid 3 15 0 00 r[15]=rowid
41 MakeRecord 13 3 1 00 r[1]=mkrec(r[13..15])
42 IdxInsert 10 1 0 10 key=r[1]
43 Next 3 38 0 03
44 Integer 0 16 0 00 r[16]=0; init LEFT JOIN no-match flag
45 Rowid 0 17 0 00 r[17]=rowid
46 SeekGE 10 80 17 1 00 key=r[17]
47 IdxGT 10 80 17 1 00 key=r[17]
48 Integer 1 16 0 00 r[16]=1; record LEFT JOIN hit
49 Integer 0 18 0 00 r[18]=0; init LEFT JOIN no-match flag
50 Column 10 1 19 00 r[19]=subject_entries_entry.subjectId
51 SeekRowid 4 76 19 00 intkey=r[19]
52 Integer 1 18 0 00 r[18]=1; record LEFT JOIN hit
53 Integer 0 20 0 00 r[20]=0; init LEFT JOIN no-match flag
54 Rowid 0 21 0 00 r[21]=rowid
55 SeekGE 9 72 21 1 00 key=r[21]
56 IdxGT 9 72 21 1 00 key=r[21]
57 DeferredSeek 9 0 5 00 Move 5 to 9.rowid if needed
58 Integer 1 20 0 00 r[20]=1; record LEFT JOIN hit
59 Rowid 0 24 0 00 r[24]=rowid
60 Column 0 3 25 00 r[25]=entry.input
61 Column 0 4 26 00 r[26]=entry.output
62 Column 0 6 27 0 00 r[27]=entry.times_seen
63 Column 2 1 28 00 r[28]=dominant_noun.noun
64 Column 2 2 29 00 r[29]=dominant_noun.article
65 Column 2 3 30 00 r[30]=dominant_noun.isPluaral
66 Column 4 1 31 00 r[31]=subject.subjectIndex
67 Column 5 1 32 00 r[32]=last_time_visited.value
68 Column 1 1 22 00 r[22]=word_class.value
69 Column 0 5 23 00 r[23]=entry.numOfWords
70 MakeRecord 22 11 35 00 r[35]=mkrec(r[22..32])
71 SorterInsert 6 35 22 11 00 key=r[35]
72 IfPos 20 76 0 00 if r[20]>0 then r[20]-=0, goto 76
73 NullRow 5 0 0 00
74 NullRow 9 0 0 00
75 Goto 0 58 0 00
76 IfPos 18 79 0 00 if r[18]>0 then r[18]-=0, goto 79
77 NullRow 4 0 0 00
78 Goto 0 52 0 00
79 Next 10 47 0 00
80 IfPos 16 83 0 00 if r[16]>0 then r[16]-=0, goto 83
81 NullRow 10 0 0 00
82 Goto 0 48 0 00
83 IfPos 11 87 0 00 if r[11]>0 then r[11]-=0, goto 87
84 NullRow 2 0 0 00
85 NullRow 8 0 0 00
86 Goto 0 34 0 00
87 IfPos 9 91 0 00 if r[9]>0 then r[9]-=0, goto 91
88 NullRow 1 0 0 00
89 NullRow 7 0 0 00
90 Goto 0 28 0 00
91 Next 0 12 0 01
92 OpenPseudo 11 36 14 00 14 columns in r[36]
93 SorterSort 6 108 0 00
94 SorterData 6 36 11 00 r[36]=data
95 Column 11 10 34 00 r[34]=last_time_visited_value
96 Column 11 9 33 00 r[33]=subject_subjectIndex
97 Column 11 8 32 00 r[32]=dominant_noun_isPluaral
98 Column 11 7 31 00 r[31]=dominant_noun_article
99 Column 11 6 30 00 r[30]=dominant_noun_noun
100 Column 11 0 29 00 r[29]=word_class_value
101 Column 11 5 28 00 r[28]=entry_times_seen
102 Column 11 1 27 00 r[27]=entry_numOfWords
103 Column 11 4 26 00 r[26]=entry_output
104 Column 11 3 25 00 r[25]=entry_input
105 Column 11 2 24 00 r[24]=entry_id
106 ResultRow 24 11 0 00 output=r[24..34]
107 SorterNext 6 94 0 00
108 Halt 0 0 0 00
109 Transaction 0 0 348 0 01 usesStmtJournal=0
110 Integer 31 2 0 00 r[2]=31
111 String8 0 3 0 % hilfe % 00 r[3]='% hilfe %'
112 String8 0 5 0 hilfe % 00 r[5]='hilfe %'
113 String8 0 7 0 % hilfe 00 r[7]='% hilfe'
114 Goto 0 1 0 00
解释查询计划输出：
QUERY PLAN
|--SCAN TABLE entry AS entry
|--SEARCH TABLE word_class AS word_class USING INDEX sqlite_autoindex_word_class_1 (entryId=?)
|--SEARCH TABLE dominant_noun AS dominant_noun USING INDEX sqlite_autoindex_dominant_noun_1 (entryId=?)
|--SEARCH TABLE subject_entries_entry AS subject_entry USING AUTOMATIC COVERING INDEX (entryId=?)
|--SEARCH TABLE subject AS subject USING INTEGER PRIMARY KEY (rowid=?)
|--SEARCH TABLE last_time_visited AS last_time_visited USING INDEX sqlite_autoindex_last_time_visited_1 (entryId=?)
`--USE TEMP B-TREE FOR ORDER BY
分析输出：
subject||1437631
entry|IDX_b32699a03d36223ff9bad94ea6|2348382 2348382
entry|IDX_a77c7936ea412ec1958007154a|2348382 67097
entry|IDX_1b0f6266dffb9a7e6343e7faa4|2348382 2
entry|IDX_36ab3550b9e3ef647d1230affc|2348382 1174191
entry|IDX_3091789786b922bee00bbb44b1|2348382 1174191
abbr|sqlite_autoindex_abbr_1|42575 1
dominant_noun|sqlite_autoindex_dominant_noun_1|823071 1
word_class|sqlite_autoindex_word_class_1|2005516 1
subject_entries_entry|sqlite_autoindex_subject_entries_entry_1|1437631 1 1
往往需要10秒以上才能得到结果。虽然这是我第一次使用 SQLite，但 20 秒的回复时间似乎很奇怪。如果我应该提供额外的信息来解决问题，请添加评论？
您看到的查询时间较长的因素是表subject_entries_entry。它是一个标准连接表，用于将entry表中的行与表中的行相关联subject。表定义使用主键，将主题 id 放在前面，然后是条目 id ( PRIMARY KEY ("subjectId", "entryId"))。
另一方面，您的查询首先连接表中的条目 id，然后连接主题 id - 与键中的顺序相反。Sqlite 可以并且确实对连接中的表进行重新排序，以尽可能提高效率，但在本例中它没有这样做。转到输出EXPLAIN QUERY PLAN：
SEARCH TABLE subject_entries_entry AS subject_entry USING AUTOMATIC COVERING INDEX (entryId=?)
这SEARCH意味着它在索引中查找特定行，而不是查看每一个行 ( SCAN)，这正是您想要的，但该AUTOMATIC COVERING INDEX部分很糟糕。AUTOMATIC意味着查询计划程序尚未找到可以使用的现有索引，但认为使用索引比扫描表更好 - 因此它构建了一个仅针对该查询而存在的临时索引。该表看起来subject_entries_entry有很多行，因此这可能需要一段时间。
按照连接中使用的主键列的顺序重新创建表，可以大大缩短时间（与翻转列的单独索引一样，但代价是使用更多的磁盘空间）。
我对这张表的另一个建议是使它成为一个没有 ROWID 的表。普通的 sqlite 表使用 64 位整数主键（称为 rowid），无论表定义使用什么；non-INTEGER PRIMARY KEY只是UNIQUE此类表中的普通索引。对于WITHOUT ROWID，主键是表的实际主键，在这种实际 rowid 没有实际用途的情况下可以节省空间。它没有一个表和一个复制每行内容的索引，而是只有一个表。不过，这种优化不会影响查询速度，因为它使用的覆盖索引已经在索引中包含了所有需要的信息；实际的表甚至没有像现在一样在查询中查看。
我不确定是否会进一步加速 - 查看查询计划，它对其余表使用预先存在的索引，并且连接子句都很简单。我有点惊讶它没有使用索引entry(inputLang)来进行搜索而不是对该表进行扫描。也许您可以在打开SQLITE_ENABLE_STAT4的情况下重建 sqlite 库，然后使用PRAGMA 优化来重建统计表，但这会涉及到相当高级的内容，具体取决于您使用的语言（在 C 或 C++ 中容易，在其他语言中更难）。
编辑：
其他一些需要探索的事情：