SQL · Theory

AVG()()

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Theory

188/439

AVG()()

AVG()() (math) sits in a report. Riya’s job is average per subject. Write that first.

Do AVG()() (math) once by hand. GROUP BY subject. Change one input. Say the new result out loud.

AVG()() (math) exists so Riya can keep average per subject correct in a report.

AVG()() (math) shows up in a report. Name average per subject, not “a real-world scenario”.

AVG()() (math) miss — SELECT extra column not in GROUP BY. Fix it before you talk about advanced SQL.

AVG()() (math) is not a lonely heading. Riya ties it to average per subject.

Close AVG()() (math) with: “If I skip it, average per subject goes wrong like this: SELECT extra column not in GROUP BY.”

Exam tip

Board: average per subject. Dry-run AVG()() (math). Name the trap: SELECT extra column not in GROUP BY.

AVG()() — sample query

CREATE TABLE scores (id INTEGER PRIMARY KEY, marks INTEGER);
INSERT INTO scores VALUES (1, 80), (2, 90), (3, 70);
SELECT COUNT(*) AS n, AVG(marks) AS avg_marks, MAX(marks) AS top
FROM scores;

AVG()() — aggregate functions collapse many rows into one summary row.

Short notes

DefAVG()() (math) — Riya uses it for average per subject in a report.
RuleAVG()() (math) → GROUP BY subject.
RememberAVG()() (math) + the query planner (a report).
UseAVG()() (math) in a report (average per subject).
TrapAVG()() (math) — SELECT extra column not in GROUP BY.
ExAVG()() (math) → average per subject.

SQL · Theory

AVG()()

← All stacks

Theory

188/439

AVG()()

AVG()() (math) sits in a report. Riya’s job is average per subject. Write that first.

Do AVG()() (math) once by hand. GROUP BY subject. Change one input. Say the new result out loud.

AVG()() (math) exists so Riya can keep average per subject correct in a report.

AVG()() (math) shows up in a report. Name average per subject, not “a real-world scenario”.

AVG()() (math) miss — SELECT extra column not in GROUP BY. Fix it before you talk about advanced SQL.

AVG()() (math) is not a lonely heading. Riya ties it to average per subject.

Close AVG()() (math) with: “If I skip it, average per subject goes wrong like this: SELECT extra column not in GROUP BY.”

Exam tip

Board: average per subject. Dry-run AVG()() (math). Name the trap: SELECT extra column not in GROUP BY.

AVG()() — sample query

CREATE TABLE scores (id INTEGER PRIMARY KEY, marks INTEGER);
INSERT INTO scores VALUES (1, 80), (2, 90), (3, 70);
SELECT COUNT(*) AS n, AVG(marks) AS avg_marks, MAX(marks) AS top
FROM scores;

AVG()() — aggregate functions collapse many rows into one summary row.

Short notes

DefAVG()() (math) — Riya uses it for average per subject in a report.
RuleAVG()() (math) → GROUP BY subject.
RememberAVG()() (math) + the query planner (a report).
UseAVG()() (math) in a report (average per subject).
TrapAVG()() (math) — SELECT extra column not in GROUP BY.
ExAVG()() (math) → average per subject.

AVG()()

AVG()() — sample query

Short notes

Questions

AVG()()

AVG()() — sample query

Short notes

Questions