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
针对此数据库模式：
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") ;
说明结果：
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
获取结果通常需要10秒钟以上。虽然这是我第一次使用SQLite，但是20秒的回复时间似乎很奇怪。如果我应该提供更多信息以解决问题，请添加评论。
答案 0 :(得分：2)
您看到的查询时间较长的因素是subject_entries_entry表。这是一个标准联结表，用于将entry表中的行与subject表中的行相关。表定义使用一个主键，该主键将主题ID放在第一位，然后是条目ID（PRIMARY KEY ("subjectId", "entryId")）。
另一方面，您的查询将首先连接表上的条目ID，然后是主题ID（与键中的顺序相反）。 Sqlite可以并且确实对联接中的表进行重新排序以尝试尽可能地高效，但是在这种情况下，它不是这样做的。转到EXPLAIN QUERY PLAN输出：
SEARCH TABLE subject_entries_entry AS subject_entry USING AUTOMATIC COVERING INDEX (entryId=?)
SEARCH意味着它正在查找索引中的特定行，而不是查看您想要的每个索引（SCAN），但是AUTOMATIC COVERING INDEX部分很糟糕。 AUTOMATIC表示查询计划者尚未找到可以使用的现有索引，但认为使用索引比必须扫描表要好-因此它会为该查询建立一个临时的索引。看来subject_entries_entry表中有很多行，因此可能要花一些时间。
重新创建具有主键列的表，顺序与连接中使用的顺序相同，这可以节省大量时间（将单独的索引翻转即可，这会浪费更多的磁盘空间）。
我对此表的另一建议是将其设置为WITHOUT ROWID。普通的sqlite表使用64位整数主键（称为rowid），而不管表定义使用什么。非INTEGER PRIMARY KEY只是此类表中的普通UNIQUE索引。使用WITHOUT ROWID时，主键是表的实际主键，这样可以节省空间，而实际的rowid并没有真正的用途。它只具有一个表，而不是一个表和一个复制每行内容的索引。不过，这种优化不会影响查询速度，因为它使用的是 covering 索引，该索引中已经包含了所有需要的信息；实际表甚至没有在查询中查看。
我不确定是否要进一步提高速度-查看查询计划，其余表使用预先存在的索引，join子句都很简单。令我有些惊讶的是它没有使用entry(inputLang)上的索引来进行搜索而不是对该表进行扫描。也许您可以先启用SQLITE_ENABLE_STAT4来重建sqlite库，然后再使用PRAGMA optimize来重建统计表，但这取决于您所使用的语言（使用C或C ++，其他语言更难）。
编辑：
其他一些值得探索的地方：