SELECT, FROM, WHERE

Three clauses do most of everyday reading work: project columns, name the table, filter rows.

Executive summary

SELECT chooses columns, FROM chooses the table, WHERE keeps only matching rows. Filter early — don’t pull the whole table into an app to discard rows.

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Learn

SELECT customer_id, email
FROM customers
WHERE country = 'UK';

Rules of thumb:

• Prefer explicit column lists over SELECT * in production extracts.
• WHERE compares values; strings need quotes in most dialects.
• Combine conditions with AND / OR; use parentheses when mixing them.

SELECT order_id, amount
FROM orders
WHERE status = 'paid'
  AND amount >= 100;

Check

Check understanding

Which clause filters rows?

• SELECT
• FROM
• WHERE

Which practices help production extracts?

Select all that apply

• List the columns you need
• Filter with WHERE in the database
• Always use SELECT *

What to do next

1. Continue to ORDER BY and LIMIT.
2. Return to Module 1 overview if you want the full list.