SQL · Theory

first()

Theory

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first()

MIN(marks) lowest value, skips NULL. SELECT name, marks FROM students WHERE marks = (SELECT MIN(marks) FROM students); can return several students who tied.

MIN on strings is alphabetical (collation). MIN on dates is earliest.

Trap — MIN as ‘first inserted row’ — it is not, unless you MIN(id).

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

Exam tip

MIN(marks) lowest score. Subquery to get those students.

first() — sample query

-- first()
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;

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

Short notes

DefMIN = smallest non-NULL value.
RuleTies: several rows can share the min.
TrapMIN meaning ‘first row’.

-- first() 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;

first()

first() — sample query

Short notes

Questions

first()

first() — sample query

Short notes

Questions