INSERT with SELECT in MySQL - Step-by-Step Execution

Concept Flow - INSERT with SELECT

Start

↓

Run SELECT query

↓

Fetch rows from SELECT

↓

Insert each row into target table

↓

All rows inserted

↓

End

This flow shows how an INSERT statement uses a SELECT query to get rows, then inserts those rows into another table.

Execution Sample

MySQL

INSERT INTO employees_backup (id, name, salary)
SELECT id, name, salary FROM employees
WHERE salary > 50000;

This query copies employees with salary over 50000 from employees table into employees_backup table.

Execution Table

Step	Action	SELECT Result Row	INSERT Action	Rows Inserted So Far
1	Run SELECT query	id=2, name='Alice', salary=60000	Insert row into employees_backup	1
2	Run SELECT query	id=4, name='Bob', salary=70000	Insert row into employees_backup	2
3	Run SELECT query	id=5, name='Carol', salary=80000	Insert row into employees_backup	3
4	Run SELECT query	No more rows	Stop inserting	3

💡 No more rows returned by SELECT, insertion complete.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
Rows Inserted	0	1	2	3	3

Key Moments - 2 Insights

Why does the INSERT statement not have VALUES but uses SELECT instead?

Because the INSERT is using a SELECT query to get multiple rows at once, so VALUES is replaced by the SELECT result rows as shown in execution_table steps 1-3.

What happens if the SELECT query returns no rows?

No rows are inserted. The execution_table row 4 shows 'No more rows' and insertion stops immediately.

Visual Quiz - 3 Questions

Look at the execution table, how many rows have been inserted after step 2?

A 3

B 1

C 2

D 0

💡 Hint

Check the 'Rows Inserted So Far' column at step 2 in the execution_table.

At which step does the SELECT query return no more rows?

A Step 4

B Step 3

C Step 1

D Step 2

💡 Hint

Look at the 'SELECT Result Row' column in execution_table for the step showing 'No more rows'.

If the WHERE condition changed to salary > 80000, how would the 'Rows Inserted So Far' change at step 3?

A It would be 3

B It would be 0

C It would be 1

D It would be 2

💡 Hint

Refer to variable_tracker and consider which rows meet the new condition.

Concept Snapshot

INSERT with SELECT syntax:
INSERT INTO target_table (columns)
SELECT columns FROM source_table WHERE condition;

- SELECT fetches rows
- INSERT adds those rows to target
- Useful for copying or transforming data
- No VALUES keyword needed
- Stops when SELECT returns no rows

Full Transcript

This visual execution shows how an INSERT statement can use a SELECT query to insert multiple rows into a table. First, the SELECT query runs and fetches rows matching the condition. Each row from the SELECT is inserted into the target table one by one. The process continues until no more rows are returned by the SELECT. The variable tracker shows how the count of inserted rows increases step by step. Key moments clarify why VALUES is not used and what happens if no rows match. The quiz tests understanding of the insertion count and flow based on the execution table.