SQL · Theory

SUM()()

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Theory

182/439

SUM()()

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

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

Skip SUM()() (math) and SELECT extra column not in GROUP BY shows up in a report.

Arun ships SUM()() (math) in a report. That is the use case worth saying.

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

Place SUM()() (math) next to nearby SQL work — GROUP BY subject is the link.

Viva for SUM()() (math) — what it is → GROUP BY subject → the mistake (SELECT extra column not in GROUP BY).

Exam tip

For SUM()() (math): definition + a report + one failure.

SUM()() — 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;

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

Short notes

DefSUM()() (math) — Arun uses it for average per subject in a report.
RuleSUM()() (math) → GROUP BY subject.
RememberSUM()() (math) + the query planner (a report).
UseSUM()() (math) in a report (average per subject).
TrapSUM()() (math) — SELECT extra column not in GROUP BY.
ExSUM()() (math) → average per subject.

SQL · Theory

SUM()()

← All stacks

Theory

182/439

SUM()()

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

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

Skip SUM()() (math) and SELECT extra column not in GROUP BY shows up in a report.

Arun ships SUM()() (math) in a report. That is the use case worth saying.

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

Place SUM()() (math) next to nearby SQL work — GROUP BY subject is the link.

Viva for SUM()() (math) — what it is → GROUP BY subject → the mistake (SELECT extra column not in GROUP BY).

Exam tip

For SUM()() (math): definition + a report + one failure.

SUM()() — 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;

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

Short notes

DefSUM()() (math) — Arun uses it for average per subject in a report.
RuleSUM()() (math) → GROUP BY subject.
RememberSUM()() (math) + the query planner (a report).
UseSUM()() (math) in a report (average per subject).
TrapSUM()() (math) — SELECT extra column not in GROUP BY.
ExSUM()() (math) → average per subject.

SUM()()

SUM()() — sample query

Short notes

Questions

SUM()()

SUM()() — sample query

Short notes

Questions