Database Indexing The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15 Organize your Data For Faster Queries

Database Indexing The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15

Database Indexing The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15 Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3

Give me all the books by this “author” Database Indexing The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15 SELECT * FROM books WHERE author = ‘abc’ Sorted by: (Author, Title) Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3

Give me all the books by this “author” with the title starting with “z%” The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15 SELECT * FROM books WHERE author = ‘abc’ AND title LIKE ‘z%’ Sorted by: (Author, Title) Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

Give me the book by this “author” with the title “x2” The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15 SELECT * FROM books WHERE author = ‘abc’ AND title = ‘x2’ Sorted by: (Author, Title) Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

Give me the books Published in this year The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15 SELECT * FROM books WHERE published LIKE ‘%-1984’ Sorted by: (Author, Title) Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

Give me the books Published in this year The Book Th30z Book Title Author Book Title Au!or 1 2 3 4 A B x1 x2 x3 z05 z07 z11 z15 SELECT * FROM books WHERE published LIKE ‘%-1984’ Sorted by: (Author, Title) Full Table Scan Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

The Book Th30z Book Title Author 4 x3 z15 Book Title Au!or 1 2 3 A B x1 x2 z05 z07 z11 Sorted by: (Published) Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

The Book Th30z Book Title Author 4 x3 z15 Book Title Au!or 1 2 3 A B x1 x2 z05 z07 z11 Sorted by: (Published) SELECT * FROM books WHERE published LIKE ‘1984-%’ Give me the books Published in this year Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

The Book Th30z Book Title Author 4 x3 z15 Book Title Au!or 1 2 3 A B x1 x2 z05 z07 z11 Sorted by: (Published) SELECT * FROM books WHERE published > ’1984-Mar-01’ AND published < ’1985-Sep-01’ Give me the books Published in this period Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

The Book Th30z Book Title Author 4 x3 z15 Book Title Au!or 1 2 3 A B x1 x2 z05 z07 z11 Sorted by: (Published) Give me all the books by this “author” SELECT * FROM books WHERE author = ‘abc’ Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

The Book Th30z Book Title Author 4 x3 z15 Book Title Au!or 1 2 3 A B x1 x2 z05 z07 z11 Sorted by: (Published) Give me all the books by this “author” SELECT * FROM books WHERE author = ‘abc’ Full Table Scan Books Table Author: Sir write-a-lot Title: Made up stuff Category: Science fiction Publisher: Cool Stuff Press Published: 1984-Jan-09 ISBN: 123-4-56-789012-3 Database Indexing

A1 117 A2 43 A3 178 B1 79 B2 48 C1 176 C2 200 C3 190 C4 89 D1 233 D2 77 a b c aaaa bbbb cccc dddd eeee ffff gggg hhhh iiii rrrr zzzz Single key If the data is sorted, the database can perform “range queries” really fast WHERE a LIKE ‘%50’ The key is used to identify the “start” Then each row is checked on the condition (b = 200) WHERE b = 2 The prefix of key is used. Then a scan in that range is performed WHERE c = ‘dddd’ WHERE a LIKE ‘C%’ WHERE a > ‘B1’ AND b = 200 Full Table Scan: The index cannot be used each row in the table will be read. Full Table Scan: The index cannot be used each row in the table will be read. Full Table Scan: The column is not indexed each row in the table will be read. WHERE a > ‘B1’ AND a < ‘C3’ The key is used to identify the “start” and the “end” Then a scan is performed on that range WHERE a > ‘B1’ The key is used to identify the “start” Then a scan is performed from that row onwards The key is used WHERE a = ‘B2’ Database Indexing

M 1 117 M 2 43 M 3 178 Q 1 79 Q 2 48 R 1 176 R 2 200 R 3 190 R 4 89 Z 1 233 Z 2 77 a b c d aaaa bbbb cccc dddd eeee ffff gggg hhhh iiii rrrr zzzz Compound key The columns order is important. (a, b) is different from (b, a) WHERE a LIKE ‘%xyz’ The prefix of key is used. Then a scan in that range is performed WHERE b = 2 The prefix of key is used. Then a scan in that range is performed WHERE c = 200 WHERE a LIKE ‘xyz%’ WHERE a = ‘M’ Full Table Scan: The index cannot be used each row in the table will be read. Full Table Scan: The index cannot be used each row in the table will be read. Full Table Scan: The column is not indexed each row in the table will be read. WHERE a = ‘R’ AND b > 10 The full key is used. Then a scan is performed from that row onwards WHERE (a > ‘O’ AND a < ’S') AND (b > 10) The prefix of key is used, to identify the a range Then each row is checked on the condition (b > 10) The full key is used WHERE a = ‘M’ AND b = 3 Database Indexing

(M, 2) 43 48 77 79 89 (R, 4) 117 176 178 190 (Z, 2) 200 233 c (Q, 2) (Q, 1) PK ref (R, 2) (R, 1) (R, 3) (Z, 1) (M, 3) (M, 1) index_on_c M 1 117 M 2 43 M 3 178 Q 1 79 Q 2 48 R 1 176 R 2 200 R 3 190 R 4 89 Z 1 233 Z 2 77 a b c d aaaa bbbb cccc dddd eeee ffff gggg hhhh iiii rrrr zzzz table_pk_a_b SELECT a, b, c, d FROM table WHERE c > 70 AND c < 150 Secondary Index for each Row maching “there will be a lookup“ on the primary key Database Indexing Clustered Index Non-Clustered Index

SELECT c, d FROM table WHERE c > 70 AND c < 150 M 1 117 M 2 43 M 3 178 Q 1 79 Q 2 48 R 1 176 R 2 200 R 3 190 R 4 89 Z 1 233 Z 2 77 a b c d aaaa bbbb cccc dddd eeee ffff gggg hhhh iiii rrrr zzzz table_pk_a_b (M, 2) 43 48 77 79 89 (R, 4) 117 176 178 190 (Z, 2) 200 233 c (Q, 2) (Q, 1) PK ref (R, 2) (R, 1) (R, 3) (Z, 1) (M, 3) (M, 1) index_on_c_d aaaa bbbb eeee cccc dddd ffff gggg hhhh iiii rrrr zzzz d Index with Included Columns If our query uses an index but it always selects a couple of fields we can “embed” them into the index (Only the index is used) Database Indexing

Database Indexing There may be better indexes but the “Range Index” B+Tree (LSM Tree) that you find in every Relational and NoSQL is a good default for every kind of query Databases tends to have more reads than writes M 1 117 M 2 43 M 3 79 Q 1 79 Q 2 48 R 1 176 R 2 200 R 3 190 R 4 89 Z 1 233 Z 2 77 Know what queries you need to support! The best way to design a database table/index is to