INSERT with RETURNING clause in PostgreSQL - Step-by-Step Execution

Concept Flow - INSERT with RETURNING clause

Start INSERT command

↓

Insert new row into table

↓

RETURNING clause triggers

↓

Return specified columns of inserted row

↓

Display returned data as query result

↓

End

The INSERT command adds a new row, then RETURNING outputs specified columns from that new row as the query result.

Execution Sample

PostgreSQL

INSERT INTO users (name, age) VALUES ('Alice', 30) RETURNING id, name;

Insert a new user named Alice aged 30, then return the new user's id and name.

Execution Table

Step	Action	Table State	RETURNING Output
1	Start INSERT command	users table unchanged
2	Insert row (name='Alice', age=30)	users table + new row (id=auto)
3	RETURNING clause fetches id and name	users table with new row	id=101, name='Alice'
4	Query returns the new row's id and name	users table with new row	id=101, name='Alice'
5	End of execution	users table with new row

💡 Insertion complete and RETURNING clause output displayed as query result

Variable Tracker

Variable	Start	After Insert	After RETURNING	Final
new_row	null	{name: 'Alice', age: 30, id: 101}	{id: 101, name: 'Alice'}	{id: 101, name: 'Alice'}

Key Moments - 2 Insights

Why do we get output from an INSERT query when using RETURNING?

Because the RETURNING clause tells PostgreSQL to send back specified columns from the newly inserted row as the query result, as shown in execution_table rows 3 and 4.

Does the RETURNING clause change the data inserted into the table?

No, RETURNING only outputs data after insertion; it does not modify the inserted data. The table state changes only at step 2 in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what does the RETURNING clause output?

A The id and name of the inserted row

B The entire users table

C Only the id column of all rows

D No output, just inserts data

💡 Hint

Check the 'RETURNING Output' column at step 3 in the execution_table

At which step does the new row actually get added to the users table?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Table State' column in the execution_table to see when the table changes

If we remove the RETURNING clause, what changes in the execution_table?

A No row is inserted

B No output is returned after insertion

C The table state does not change

D The inserted row is returned by default

💡 Hint

RETURNING clause controls output; without it, no data is returned after insert

Concept Snapshot

INSERT INTO table (columns) VALUES (values) RETURNING columns;
- Inserts a new row into the table.
- RETURNING outputs specified columns from the inserted row.
- Useful to get auto-generated IDs or inserted data immediately.
- Without RETURNING, INSERT returns no rows.
- Works only in PostgreSQL and some other DBs supporting RETURNING.

Full Transcript

This visual execution shows how the INSERT statement with RETURNING clause works in PostgreSQL. First, the INSERT command starts and adds a new row to the users table with the given values. Then, the RETURNING clause fetches specified columns from the newly inserted row, such as id and name. This data is returned as the query result. The table state changes only when the row is inserted, and RETURNING does not modify data but only outputs it. This helps to immediately get values like auto-generated IDs after insertion.

Practice

1. What does the RETURNING clause do in a PostgreSQL INSERT statement?

easy

A. It creates a backup of the inserted data.

B. It deletes rows after insertion.

C. It updates existing rows instead of inserting.

D. It returns specified columns of the newly inserted rows immediately.

Solution

1. Step 1: Understand the purpose of RETURNING

   The RETURNING clause in PostgreSQL is used to get back specified columns from the rows that were just inserted.

2. Step 2: Compare with other options

   The other options describe actions unrelated to RETURNING. RETURNING does not delete, update, or backup data.

3. Final Answer:

   It returns specified columns of the newly inserted rows immediately. -> Option D

4. Quick Check:

   RETURNING returns inserted data [OK]

Hint: RETURNING fetches inserted row data instantly [OK]

Common Mistakes:

• Thinking RETURNING deletes or updates data
• Confusing RETURNING with SELECT
• Assuming RETURNING creates backups

2. Which of the following is the correct syntax to insert a row and return the generated id in PostgreSQL?

easy

A. INSERT INTO users VALUES ('Alice') RETURNING id;

B. INSERT INTO users (name) RETURN id VALUES ('Alice');

C. INSERT INTO users (name) VALUES ('Alice') RETURNING id;

D. INSERT INTO users (name) VALUES ('Alice') RETURN id;

Solution

1. Step 1: Check correct RETURNING syntax

   The correct syntax places RETURNING after VALUES and specifies the column to return, like RETURNING id.

2. Step 2: Validate each option

   INSERT INTO users (name) VALUES ('Alice') RETURNING id; matches the correct syntax. Placing RETURNING before VALUES or using RETURN instead of RETURNING is incorrect. INSERT INTO users VALUES ('Alice') RETURNING id; misses column list before VALUES.

3. Final Answer:

   INSERT INTO users (name) VALUES ('Alice') RETURNING id; -> Option C

4. Quick Check:

   RETURNING follows VALUES with column list [OK]

Hint: RETURNING goes right after VALUES clause [OK]

Common Mistakes:

• Placing RETURNING before VALUES
• Omitting column list in INSERT
• Using RETURN instead of RETURNING

3. Given the table products(id SERIAL PRIMARY KEY, name TEXT, price NUMERIC), what will this query return?

INSERT INTO products (name, price) VALUES ('Pen', 1.5) RETURNING id, price;

medium

A. The new product's id and price, e.g., (5, 1.5)

B. Only the id of the new product

C. An error because RETURNING can't return multiple columns

D. Nothing, INSERT does not return rows

Solution

1. Step 1: Understand RETURNING with multiple columns

   RETURNING can return one or more columns from the inserted row(s). Here, id and price are requested.

2. Step 2: Predict output

   The query inserts a new product and returns its auto-generated id and the price 1.5 as a row, e.g., (5, 1.5).

3. Final Answer:

   The new product's id and price, e.g., (5, 1.5) -> Option A

4. Quick Check:

   RETURNING multiple columns returns all requested [OK]

Hint: RETURNING can list multiple columns separated by commas [OK]

Common Mistakes:

• Assuming RETURNING returns only one column
• Expecting no output from INSERT
• Thinking RETURNING causes syntax error with multiple columns

4. What is wrong with this query?

INSERT INTO orders (product_id, quantity) VALUES (10, 3) RETURNING;

medium

A. VALUES clause is incorrectly formatted.

B. RETURNING clause is missing column names to return.

C. INSERT statement cannot have RETURNING clause.

D. product_id and quantity columns do not exist.

Solution

1. Step 1: Check RETURNING syntax

   RETURNING must specify at least one column or * to return. Here, it is empty, which is invalid syntax.

2. Step 2: Verify other parts

   VALUES clause and columns look correct. INSERT supports RETURNING. Assuming columns exist, no error there.

3. Final Answer:

   RETURNING clause is missing column names to return. -> Option B

4. Quick Check:

   RETURNING needs columns or * [OK]

Hint: RETURNING must specify columns or * [OK]

Common Mistakes:

• Leaving RETURNING empty
• Confusing RETURNING with WHERE
• Assuming RETURNING is optional but empty

5. You want to insert multiple rows into employees(name, department) and get back their generated id values. Which query correctly does this and returns all new ids?

hard

A. INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURNING id;

B. INSERT INTO employees (name, department) RETURNING id VALUES ('John', 'HR'), ('Jane', 'IT');

C. INSERT INTO employees (name, department) VALUES ('John', 'HR'); RETURNING id; INSERT INTO employees (name, department) VALUES ('Jane', 'IT'); RETURNING id;

D. INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURN id;

Solution

1. Step 1: Understand multi-row INSERT with RETURNING

   PostgreSQL allows inserting multiple rows in one statement and RETURNING returns all inserted rows' specified columns.

2. Step 2: Analyze each option

   INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURNING id; correctly inserts two rows and returns their ids. INSERT INTO employees (name, department) RETURNING id VALUES ('John', 'HR'), ('Jane', 'IT'); misplaces RETURNING before VALUES. INSERT INTO employees (name, department) VALUES ('John', 'HR'); RETURNING id; INSERT INTO employees (name, department) VALUES ('Jane', 'IT'); RETURNING id; splits inserts and RETURNING incorrectly. INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURN id; uses invalid RETURN keyword.

3. Final Answer:

   INSERT INTO employees (name, department) VALUES ('John', 'HR'), ('Jane', 'IT') RETURNING id; -> Option A

4. Quick Check:

   Multi-row INSERT with RETURNING returns all rows [OK]

Hint: Use RETURNING after multi-row VALUES to get all ids [OK]

Common Mistakes:

• Placing RETURNING before VALUES
• Splitting inserts instead of multi-row insert
• Using RETURN instead of RETURNING