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Show Indexes

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Show Indexes

SHOW INDEX FROM students; lists indexes, columns, uniqueness, cardinality. Key_name PRIMARY is the PK.

EXPLAIN still answers ‘will this query use it?’. SHOW INDEX answers ‘what exists?’.

Trap — looking at cardinality 2 on a boolean and expecting miracles.

On the example next to this theory: Show Indexes: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

SHOW INDEX FROM students;

Show Indexes — sample query

-- Show Indexes
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

Show Indexes: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

DefSHOW INDEX FROM t; lists indexes.
RulePRIMARY is an index too.
TrapHigh hopes on low-cardinality indexes.

-- Show Indexes CREATE TABLE demo ( id INTEGER PRIMARY KEY, label TEXT NOT NULL, qty INTEGER DEFAULT 0 ); INSERT INTO demo (id, label, qty) VALUES (1, 'alpha', 2), (2, 'beta', 5); SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

Show Indexes

Show Indexes — sample query

Short notes

Questions

Show Indexes

Show Indexes — sample query

Short notes

Questions