Filtering and Sorting

Most of the time you do not want the whole table. Filtering narrows rows; sorting decides the order they come back in.

WHERE

Use comparison operators to keep matching rows. String values go in single quotes; numbers do not.

SELECT name, score
FROM students
WHERE score >= 70;

Combining Conditions

Use AND when both conditions must hold, OR when either may. Parentheses make the intention clear.

SELECT name, level, score
FROM students
WHERE level = 'SS2'
  AND (score >= 70 OR score IS NULL);

Pattern Matching

LIKE matches text. % means any number of characters and _ means exactly one.

SELECT name
FROM students
WHERE name LIKE 'A%';

SELECT name
FROM students
WHERE name LIKE '%olu%';

Sorting

ORDER BY sorts ascending by default. Use DESC for highest first and add a second column as a tie-breaker.

SELECT name, score
FROM students
ORDER BY score DESC, name ASC;

Practice

1. Find students in SS1 with a score above 60.
2. List names starting with B.
3. Sort students by level, then by name.

Hands-on exercise

Write a query that returns name and score from students where:
1. score is at least 50.
2. level is either SS2 or SS3.
Sort by score from highest to lowest.

Recap

WHERE chooses rows, LIKE searches text and ORDER BY arranges the result. Use IS NULL for missing values.