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Coding — SQL and Databases

SQL syntax, queries, and database design concepts

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sql_selectstar 15 terms Feb 17, 2026
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Terms 15

1
SELECT
Retrieves data from one or more tables; SELECT col FROM table
2
WHERE
Filters rows based on a condition; SELECT * FROM t WHERE age > 18
3
JOIN
Combines rows from multiple tables based on a related column
4
INNER JOIN
Returns rows with matching values in both tables
5
LEFT JOIN
Returns all rows from left table; matching rows from right; NULLs if no match
6
GROUP BY
Groups rows sharing a value; used with aggregate functions
7
HAVING
Filters groups after GROUP BY; like WHERE but for aggregated data
8
ORDER BY
Sorts result set; ASC (ascending) or DESC (descending)
9
COUNT()
Counts number of rows matching criteria
10
SUM() / AVG()
Aggregate functions calculating total or average of a column
11
Primary Key
Unique identifier for each row in a table; cannot be NULL
12
Foreign Key
Column referencing primary key of another table; establishes relationship
13
Normalization
Organizing database to reduce redundancy; 1NF, 2NF, 3NF
14
Index
Data structure speeding up queries on specific columns
15
Transaction
Group of SQL operations executed as a single unit; ACID properties