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BeginnerQuerying basics

SELECT and columns

Choose exactly the columns you want, rename them, and remove duplicates.

SQLBeginner7 min read
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By the end of this lesson you will be able to:
  • Project specific columns with SELECT
  • Rename output columns with AS
  • Remove duplicate rows with DISTINCT

SELECT is how you ask for data. SELECT * returns every column; usually you want only some. List the columns you care about, comma-separated:

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Choosing columns (called projection) keeps results focused and is clearer than * for anything beyond a quick look on a .

Renaming with AS

Give an output column a friendlier name with AS — useful for computed values:

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You can compute columns too. Prices are per-item; here's each product with a "price in pence":

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Removing duplicates with DISTINCT

DISTINCT collapses identical rows to one — handy for "what are the distinct values?":

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Without DISTINCT you'd see UK and US twice (two customers each). With it, each country appears once.

Where to go next

You can pick columns; next, pick rows — filtering with WHERE.

Finished reading? Mark it complete to track your progress.

The relational model

Tables, rows, columns, and keys — the simple, powerful idea under every SQL database.

Filtering with WHERE

Keep only the rows you want — comparisons, AND/OR, IN, BETWEEN, LIKE, and NULL.

On this page

Renaming with ASRemoving duplicates with DISTINCTWhere to go next