SQL: Queries

Exactly the rows you asked for

One table, and every clause that acts on it. Four modules of saying what a query returns — how many rows, which columns, in what order — on questions generated fresh that never run out. Then a SQL prompt of your own, twenty-four real rows in it, and questions to put to them.

Start this project See the modules

Modules: 6
Drills: 9
Build steps: 7
Time: ~3h

Walk out able to

Read a single-table `SELECT` and name the rows it returns before running it — then write the one query that answers a question somebody actually asked.

What you drill

Predicates that mean it

AND, OR, NOT, brackets, BETWEEN, IN and both wildcards.

Order, ties and pages

Second keys that decide, and the arithmetic under OFFSET.

Columns, values, totals

Projection, DISTINCT, computed columns and six aggregates.

A prompt of your own

Load a 24-row table and put real questions to it.

What you get

Skills that stick

Every project mixes short lessons, focused drills and real build steps, so you finish with working code and the judgement behind it.

You will practise

Rows returned, with and without DISTINCT
WHERE: AND, OR, NOT, BETWEEN, IN, LIKE
ORDER BY with ties, and LIMIT arithmetic
Aliases, aggregates, clauses spelled right

Afterwards you can

Say what a SELECT returns before running it
Read an unbracketed AND beside an OR correctly
Turn a page number into the right OFFSET
Answer a stated question with one query

Modules

Step by step

Each module builds on the last. Read a short lesson, drill it until it's second nature, then put it to work.

1
Say what comes back
~27 min
Read a SELECT and name the rows and columns it returns, repeats and all.
- LessonWhat a query hands back11 min
- LessonDuplicates, and DISTINCT7 min
- DrillCount the rows, then the values9 min
2
Filter rows with WHERE
~34 min
Run a predicate down a table and get the count right, brackets or no brackets.
- DrillKeep only the matching rows11 min
- DrillSettle it without brackets12 min
- DrillMatch a range, a set, a pattern11 min
3
Order it, then cut it
~20 min
Break a tie on purpose, and say which rows a given page of a result holds.
- DrillBreak a tie on purpose12 min
- DrillTake the page you asked for8 min
4
Compute, name and total
~49 min
Name a computed column, total a table, and spell the clause from memory.
- LessonName a column you computed12 min
- LessonOne number out of every row8 min
- DrillPut it where the clause sees it8 min
- DrillCollapse a table to one number10 min
- DrillSpell the clause from memory11 min
5
Get a prompt and load it
~13 min
Put a real SQL engine in front of you, and put the shop table into it.
- Build stepGet a SQL prompt of your own6 min
- Build stepLoad the shop table7 min
6
Four questions, then your own
~44 min
Write and run the query each one needs, then ask the table something of your own.
- Build stepFilter it down and order it10 min
- Build stepPage through the result8 min
- Build stepValue the whole shelf10 min
- Build stepTotal one aisle8 min
- Build stepAsk it something of your own8 min