Select Basics

Select Columns from Orders

Column Checklist

Use the steps as a column checklist:

  1. In the input table, mark the columns named by the query.
  2. Carry those columns across in the same row order.
  3. Leave the unselected columns behind. This is a shape change, not a row test. Every order row still appears; only the visible fields are narrower.

Projection keeps requested columns and drops the rest.

highlighted = computed this step

Input table

Start with Orders, which has identifiers, categories, and amounts.

Orders\text{Orders}
Ordersorder_idcategoryamounto1book20o2book35o3pen5

Select query

Select only the identifier and amount columns.

SELECT order_id, amount\text{SELECT order\_id, amount}
SELECT chosen columnsselect order_id,amountarity 2 rows 3Ordersarity 3 rows 3

Output table

The category column is gone; row count is unchanged.

projected columns\text{projected columns}
Outputorder_idamounto120o235o35