SQL · Theory

regexp_substr()

Theory

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regexp_substr()

regexp_substr() is pattern matching. LIKE uses % and _. REGEXP / RLIKE uses regular expressions (e.g. name REGEXP '^[A-Z]'). They are not interchangeable.

REGEXP_LIKE, REGEXP_REPLACE, REGEXP_SUBSTR, REGEXP_INSTR are MySQL 8 helpers. Don’t write Java-style /pattern/g.

Trap — LIKE with regex stars. Trap: REGEXP on a huge unindexed column.

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

Exam tip

LIKE vs REGEXP in one sentence, plus one example.

regexp_substr() — sample query

-- regexp_substr()
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;

regexp_substr(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

Defregexp_substr() matches text by a pattern.
RuleLIKE = % _. REGEXP = regular expressions.
TrapMixing LIKE wildcards with regex.

-- regexp_substr() 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;

regexp_substr()

regexp_substr() — sample query

Short notes

Questions

regexp_substr()

regexp_substr() — sample query

Short notes

Questions