Multiple Columns and Aliases

A SELECT produces a table — even when it's computing expressions — and this lesson is about controlling that table's shape: how many columns, computed how, named what. Naming, it turns out, is not cosmetic.

Multiple values per row

Separate expressions with commas; each becomes a column:

SELECT 'Ada', 1815, 2 * 18;
-- one row: | Ada | 1815 | 36 |

Order matters — columns come out in the order you asked. From a table, the same idea selects specific columns:

SELECT name, population FROM cities;

You'll also meet SELECT * — "every column." Fine for exploring; frowned on in real code (schemas change; * silently changes with them). Name what you need.

Expressions on columns

Any column can be computed from others — arithmetic, functions, concatenation:

SELECT name,
       population / 1000000,           -- millions (integer division! see below)
       UPPER(country)
FROM cities;

The scalar-function starter pack: UPPER(s) / LOWER(s), LENGTH(s), ROUND(x, digits), ABS(x), and || for concatenation. One arithmetic honesty note: dividing two integers gives an integer in SQLite (7 / 2 → 3); write population / 1000000.0 when you want decimals — the same truncation trap as every other language in this catalog.

Aliases: AS

Computed columns get ugly automatic names (population / 1000000.0 becomes the literal expression text). AS names them:

SELECT name,
       population / 1000000.0 AS millions,
       'City: ' || name AS label
FROM cities;

Three reasons aliases matter beyond looks:

1. Graders check column names on many exercises — AS greeting isn't optional if the expected output says greeting.
2. Later clauses can refer to them — ORDER BY millions reads better than repeating the expression.
3. Applications read columns by name — the alias is the API you're giving whatever code runs the query.

The AS keyword itself is optional (population AS pop ≡ population pop) but write it — the explicit form survives code review everywhere. Aliases with spaces need double quotes (AS "in millions") — remember, double quotes are for identifiers.

Your exercise: Build a Greeting

Produce a greeting assembled from pieces with ||, under the exact column name the spec shows. The assembly line: string literals in single quotes, || between parts, AS to name the result. Spacing bugs live inside your quoted literals ('Hello,' || name vs 'Hello, ' || name) — when the output is one space off, the space is missing from a literal, not from SQL.