BeginnerQuerying basics
Filtering with WHERE
Keep only the rows you want — comparisons, AND/OR, IN, BETWEEN, LIKE, and NULL.
SQLBeginner9 min read
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By the end of this lesson you will be able to:
- Filter rows with WHERE and comparison operators
- Combine conditions with AND / OR
- Use IN, BETWEEN, LIKE, and IS NULL
WHERE keeps only the rows that match a condition. It comes after the table and
before sorting:
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Comparisons and combining
The usual operators work: =, <> (not equal), <, >, <=, >=. Combine
conditions with AND and OR (use parentheses when mixing them):
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String values go in single quotes ('US'). Double quotes mean something
different in SQL (an identifier), so "US" will usually error or misbehave.
Handy shorthands
- IN — match any of a list:
country IN ('US', 'NL'). - BETWEEN — an inclusive range:
price BETWEEN 2 AND 5. - LIKE — pattern match, where
%is any text:name LIKE 'A%'(starts with A).
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NULL is special
NULL means "no value," and it doesn't compare with =. Use IS NULL /
IS NOT NULL:
SELECT name FROM customers WHERE country IS NULL; -- not = NULLcountry = NULL is never true — a classic SQL gotcha.
Where to go next
Now order and trim the results: sorting and limiting.
Finished reading? Mark it complete to track your progress.