SQL lesson
INSERT, UPDATE, DELETE, and RETURNING
Practice INSERT, UPDATE, DELETE, and RETURNING with a worked query, common mistakes, and a checked next step. Make targeted state changes and inspect affected rows inside rollback-safe checks.
What you will learn
Make targeted state changes and inspect affected rows inside rollback-safe checks.
Before writing SQL, name what one result row should mean for INSERT, UPDATE, DELETE, and RETURNING.
Learning objectives and prerequisites
Each objective names an observable SQL behavior, with prerequisite topics linked in the order you need them.
Plan about 20 minutes for the explanation, worked example, prediction, and first hands-on attempt. Delayed review adds practice later.
- Objective: Make targeted state changes and inspect affected rows inside rollback-safe checks.
- Skill focus: dml-returning
- Prerequisite: review Logical Processing Order, Systematic Debugging, and Data Quality before this lesson.
Example query and result
Study the compact worked query first, then open the editor when you are ready to change and run it.
- Starting rows: one target row or statement result in a controlled transaction.
- Result rows: one verified mutation or plan-inspection result.
BEGIN; UPDATE tickets SET status = 'reviewed' WHERE ticket_id = 101 RETURNING ticket_id, status; ROLLBACK;| Example output | Meaning |
|---|---|
| 101 | reviewed | changed row is visible through RETURNING |
| rollback | public example keeps the data repair reversible |
Syntax pattern
Use the syntax pattern as a shape, not as a memorized answer. Replace table, column, condition, grouping, and ordering names according to the stated grain.
BEGIN; UPDATE table_name SET column_name = value WHERE key = $1 RETURNING *; ROLLBACK;| Input grain | Output grain | Validation focus |
|---|---|---|
| one target row or statement result in a controlled transaction | one verified mutation or plan-inspection result | Rows, order, duplicates, nulls, and edge cases |
Common mistakes and why they fail
A common mistake is matching the visible rows while ignoring ordering, duplicate policy, null behavior, tie behavior, or the stated result grain.
Why it fails: INSERT, UPDATE, DELETE, and RETURNING checks changed examples, so a query that only copies visible rows can break when row counts, labels, nulls, or ties change.
PostgreSQL dialect notes stay explicit when syntax, date handling, transaction behavior, or comparison semantics matter.
Predict the result before you run it
Before opening the app, predict the output grain, the first column, and one edge case that could change the answer.
This is a reading prompt only; the app opens only when you choose to practice.
- Prediction: name one row that should appear or one row that should be excluded.
- Check: explain whether nulls, duplicates, ties, or missing relationships affect the result.
- Transfer: say what would change on a second dataset with different labels and counts.
Practice and related resources
Move to the app when you want the editor, checks, hints, and solution review.
Page highlights
- Clear task requirements
- Learning objectives and prerequisite links
- Original worked query and readable result example
- What each result row means
- Misconception and edge-case notes
- Predict the result before running the query
- Previous and next lesson navigation