Master B-tree, composite, clustered, cardinality, and selectivity — the database indexing vocabulary essential for query optimisation conversations.
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How is 'B-tree' pronounced?
B-tree is pronounced /biː triː/ — 'BEE TREE'. 'B' is the letter B = /biː/. 'tree' is the common English word = /triː/. Together: 'BEE TREE'. The 'B' in B-tree likely stands for 'balanced', though it may also refer to Boeing or Bayer (its inventors). Two words: BEE + TREE. A B-tree is a self-balancing tree data structure that maintains sorted data and allows searches, insertions, deletions, and sequential access in O(log n) time. B-trees are the fundamental data structure underlying most database index implementations.
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How is 'composite' pronounced in a database context?
Composite is pronounced /kəmˈpɒzɪt/ — 'kum-POZ-it'. From Latin 'compositus' (put together). 'Com' = /kəm/ (schwa, unstressed). 'pos' = /pɒz/ (short /ɒ/, stressed). '-ite' = /ɪt/ (short /ɪ/). Three syllables: kum-POZ-it, stress on the second. In database indexing, a composite index (also called a multi-column or compound index) is an index on two or more columns. The column order matters: a composite index on (last_name, first_name) is useful for queries filtering on last_name but not for queries filtering only on first_name.
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How is 'clustered' pronounced?
Clustered is pronounced /ˈklʌstərd/ — 'KLUS-turd'. From 'cluster' (a group close together) + '-ed'. 'Clus' = /klʌs/ (short /ʌ/ as in 'cup'). '-tered' = /tərd/ (schwa + rhotic). Two syllables: KLUS-turd, stress on the first. In databases, a clustered index determines the physical order of data in a table — the table rows are stored in index-key order. SQL Server and MySQL InnoDB tables have exactly one clustered index per table; PostgreSQL achieves similar effects using the CLUSTER command.
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How is 'cardinality' pronounced?
Cardinality is pronounced /ˌkɑːrdɪˈnælɪti/ — 'kar-dih-NAL-ih-tee'. From Latin 'cardinalis' (principal, pivotal). 'Car' = /kɑːr/ (rhotic vowel). 'di' = /dɪ/. 'nal' = /næl/ (short /æ/, stressed). '-ity' = /ɪti/. Five syllables: kar-dih-NAL-ih-tee, stress on the third. In databases, cardinality refers to the uniqueness of data values in a column — high cardinality (many unique values, like user IDs) makes an index very selective and efficient; low cardinality (few unique values, like boolean fields) makes an index less useful for filtering.
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How is 'selectivity' pronounced?
Selectivity is pronounced /sɪˌlɛktɪˈvɪti/ — 'sih-lek-tih-VIT-ee'. From 'selective' + '-ity'. 'Si' = /sɪ/. 'lec' = /lɛk/ (short /ɛ/). 'ti' = /tɪ/. 'vit' = /vɪt/ (stressed). '-y' = /i/. Five syllables: sih-lek-tih-VIT-ee, stress on the fourth. In database query optimisation, selectivity is the fraction of rows that match a query predicate — high selectivity means few rows match (the filter is very specific), making an index scan efficient. Low selectivity means many rows match, often making a full table scan cheaper than using the index.