SQL
SELECT
SELECT projects columns from rows.
REFERENCE CATEGORY
SQL
19 practical topics
SQL
INSERT
INSERT creates rows.
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UPDATE
UPDATE changes matching rows.
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DELETE
DELETE removes matching rows.
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WHERE
WHERE filters individual rows before grouping.
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JOIN
JOIN combines rows using related keys.
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GROUP BY
GROUP BY collects rows for aggregate calculations.
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ORDER BY
ORDER BY defines result ordering.
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LIMIT
LIMIT bounds rows returned.
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Aggregation
Aggregates compute count, sum, min, max, or average.
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Subqueries
A subquery nests a query inside another query.
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Constraints
Constraints enforce integrity independently of application code.
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Primary keys
A primary key uniquely identifies a row.
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Foreign keys
Foreign keys require referenced records to exist.
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Unique constraints
Unique constraints prevent duplicate keys at the database boundary.
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Indexes
Indexes accelerate selected reads at a write/storage cost.
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Transactions
Transactions commit or roll back a set of writes.
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Isolation
Isolation controls how concurrent transactions observe/interfere with each other.
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ACID
ACID means atomicity, consistency, isolation, and durability.