SQL · Theory

sum()

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Theory

119/439

sum()

sum() is simple if you keep it on paper. Asha uses it for average per subject in a report.

For sum(), the query planner is in play. Don’t blame it until you have traced average per subject.

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

Asha ships sum() in a report. That is the use case worth saying.

If average per subject breaks under sum(), check SELECT extra column not in GROUP BY first.

sum() is not a lonely heading. Asha ties it to average per subject.

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

Exam tip

For sum(): 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() — Asha uses it for average per subject in a report.
Rulesum() → GROUP BY subject.
Remembersum() + the query planner (a report).
Usesum() in a report (average per subject).
Trapsum() — SELECT extra column not in GROUP BY.
Exsum() → average per subject.

SQL · Theory

sum()

← All stacks

Theory

119/439

sum()

sum() is simple if you keep it on paper. Asha uses it for average per subject in a report.

For sum(), the query planner is in play. Don’t blame it until you have traced average per subject.

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

Asha ships sum() in a report. That is the use case worth saying.

If average per subject breaks under sum(), check SELECT extra column not in GROUP BY first.

sum() is not a lonely heading. Asha ties it to average per subject.

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

Exam tip

For sum(): 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() — Asha uses it for average per subject in a report.
Rulesum() → GROUP BY subject.
Remembersum() + the query planner (a report).
Usesum() in a report (average per subject).
Trapsum() — SELECT extra column not in GROUP BY.
Exsum() → average per subject.

sum()

sum() — sample query

Short notes

Questions

sum()

sum() — sample query

Short notes

Questions