Section 6 · SQL · Topic 1 of 2 · about 25 min

Querying with SQL

Select, filter and sort rows from a table with SELECT, WHERE and ORDER BY. Interactive lessons let you practise in the browser without installing anything.

Difficulty: Intermediate
Complexity 3 of 5
Time to complete: about 25 min

Start learning

You will be able to

Select columns and filter rows with WHERE
Sort and limit results
Write clauses in the right order

What you will learn

Why this matters

In SQL interview tests, the first questions are almost always about selecting, filtering and sorting rows. These few keywords do a large share of everyday analyst work, so practise them until they feel natural.

The example table

Imagine an invented table called sales for a chain of provision shops in the north:

| sale_id | shop | town | item | qty | amount | |---|---|---|---|---|---| | 1 | Shop A | Tamale | Rice | 2 | 180 | | 2 | Shop B | Wa | Oil | 1 | 95 |

SELECT and FROM

SELECT names the columns you want; FROM names the table.

SELECT town, item, amount
FROM sales;

SELECT * returns every column. It is handy for a quick look, but naming columns keeps results small and clear.

WHERE: filtering rows

WHERE keeps only rows that meet a condition.

SELECT item, amount
FROM sales
WHERE town = 'Tamale' AND amount >= 100;

Text values go inside single quotes. You can combine conditions with AND and OR, and use comparisons such as =, <>, <, >, <= and >=. Other useful filters:

IN ('Tamale', 'Wa') matches any value in a list.
BETWEEN 50 AND 200 matches a range, including both ends.

Section 6 · SQL · Topic 1 of 2 · about 25 min

Querying with SQL

Select, filter and sort rows from a table with SELECT, WHERE and ORDER BY. Interactive lessons let you practise in the browser without installing anything.

Difficulty: Intermediate
Complexity 3 of 5
Time to complete: about 25 min

Start learning

You will be able to

Select columns and filter rows with WHERE
Sort and limit results
Write clauses in the right order

What you will learn

Why this matters

The example table

Imagine an invented table called sales for a chain of provision shops in the north:

| sale_id | shop | town | item | qty | amount | |---|---|---|---|---|---| | 1 | Shop A | Tamale | Rice | 2 | 180 | | 2 | Shop B | Wa | Oil | 1 | 95 |

SELECT and FROM

SELECT names the columns you want; FROM names the table.

SELECT town, item, amount
FROM sales;

SELECT * returns every column. It is handy for a quick look, but naming columns keeps results small and clear.

WHERE: filtering rows

WHERE keeps only rows that meet a condition.

SELECT item, amount
FROM sales
WHERE town = 'Tamale' AND amount >= 100;

Text values go inside single quotes. You can combine conditions with AND and OR, and use comparisons such as =, <>, <, >, <= and >=. Other useful filters:

IN ('Tamale', 'Wa') matches any value in a list.
BETWEEN 50 AND 200 matches a range, including both ends.

Querying with SQL

You will be able to

What you will learn

Why this matters

The example table

SELECT and FROM

WHERE: filtering rows

Querying with SQL

You will be able to

What you will learn

Why this matters

The example table

SELECT and FROM

WHERE: filtering rows

ORDER BY and LIMIT

DISTINCT and aliases

The order of clauses

A worked example

Habits of a careful querier

Practice task

Free resources