Tauseef FayyazA to Z
Glossary
Every concept in this sheet, plus the smaller terms it uses. Select a concept to open its card.
C
- CASE expression
- CASE returns a value based on conditions checked in order, like if and else inside a query.
- Command-line client
- A terminal program that connects to the database server and runs SQL you type or pipe in: psql for PostgreSQL, mysql for MySQL, sqlcmd for SQL Server.
D
- DDL, DML and DCL
- The families of SQL statements: DDL defines structure (CREATE, ALTER, DROP), DML reads and changes rows (SELECT, INSERT, UPDATE, DELETE), DCL grants access (GRANT, REVOKE) and transaction control groups changes (COMMIT, ROLLBACK).
- DISTINCT
- DISTINCT removes duplicate rows from the result, comparing all selected columns together.
F
- Foreign key
- A column that stores the primary key of a row in another table, declared with a constraint so the database rejects values that do not exist there.
L
- Limiting rows
- Returning only the first N rows of a sorted result.
- Logical order of a query
- The order a query is evaluated in, which differs from the order you write it: FROM and JOIN, then WHERE, GROUP BY, HAVING, SELECT, DISTINCT, ORDER BY and finally LIMIT or TOP.
M
- MySQL Workbench
- The official graphical tool for MySQL, rebuilt in 2026 as MySQL Workbench 26 with a script editor, SQL notebooks, a visual EXPLAIN and administration screens.
N
- NULL and three-valued logic
- NULL means a value is missing or unknown.
O
- ORDER BY
- ORDER BY sorts the result by one or more columns or expressions, ascending by default or DESC for descending.
P
- Primary key
- A column, or set of columns, whose value is unique and never NULL for every row, so it identifies exactly one row.
R
- Relational model
- Data stored in tables: each table describes one kind of thing, each row is one instance of it and each column is one attribute with a fixed type.
S
- Sample database
- A ready-made database with realistic tables and thousands of rows that you load locally to practise on, such as pagila for PostgreSQL, sakila for MySQL or AdventureWorks for SQL Server.
- SELECT and FROM
- SELECT lists the columns or expressions you want back and FROM names the table they come from.
- String and date functions
- Built-in functions for text (joining, trimming, changing case, extracting parts) and for dates (current time, adding intervals, truncating to a month).
W
- WHERE
- WHERE keeps only the rows for which a condition is true, using comparisons, AND, OR, NOT, IN for a list, BETWEEN for an inclusive range and LIKE for simple patterns.