Column aliases with AS in SQL - Step-by-Step Execution

Concept Flow - Column aliases with AS

Write SELECT statement

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Specify column names

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Use AS to rename columns

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Execute query

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Result shows new column names

This flow shows how to rename columns in a query result using AS, making output easier to read.

Execution Sample

SQL

SELECT first_name AS Name, age AS AgeYears FROM users;

This query selects two columns from users and renames them using AS for clearer output.

Execution Table

Step	Action	Input	Output
1	Start query execution	SELECT first_name AS Name, age AS AgeYears FROM users;	Prepare to read users table
2	Read first row from users	Row: {first_name: 'Alice', age: 30}	Apply aliases: Name='Alice', AgeYears=30
3	Read second row from users	Row: {first_name: 'Bob', age: 25}	Apply aliases: Name='Bob', AgeYears=25
4	Read third row from users	Row: {first_name: 'Carol', age: 27}	Apply aliases: Name='Carol', AgeYears=27
5	No more rows	End of table	Return result set with aliased columns

💡 All rows processed, query returns result with columns renamed by AS

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
Name	N/A	Alice	Bob	Carol	Carol
AgeYears	N/A	30	25	27	27

Key Moments - 2 Insights

Why do we use AS in the SELECT statement?

AS lets us rename columns in the output for clarity, as shown in execution_table rows 2-4 where original column names become 'Name' and 'AgeYears'.

Does AS change the actual table column names?

No, AS only changes column names in the query result, not in the database table itself, as seen in execution_table step 1 where original columns are read.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'Name' after reading the second row?

A Alice

B Bob

C Carol

D 30

💡 Hint

Check execution_table row 3 under Output column for 'Name' value.

At which step does the query finish reading all rows?

A Step 3

B Step 4

C Step 5

D Step 2

💡 Hint

Look for the step mentioning 'No more rows' in execution_table.

If we remove AS and write SELECT first_name, age FROM users, what changes in the output?

A Column names will be original: first_name and age

B Column names will be Name and AgeYears

C Query will fail

D Output will be empty

💡 Hint

AS is used to rename columns, so removing it keeps original names as per concept_snapshot.

Concept Snapshot

SELECT column_name AS alias_name
Use AS to rename columns in query output.
Aliases improve readability without changing table.
Alias names appear in result headers.
AS keyword is optional but recommended for clarity.

Full Transcript

This lesson shows how to rename columns in SQL query results using the AS keyword. The query selects columns from a table and assigns new names to them for clearer output. The execution steps read each row from the table, apply the aliases, and return the renamed columns. Aliases do not change the actual table columns, only the output headers. This helps make query results easier to understand.