SQL Standards & Dialects

SQL is standardized by ANSI and ISO, which means there is an official specification that defines core syntax and behavior. In practice, though, every database vendor implements that standard as a baseline and then extends it with proprietary features, functions, and shortcuts. The result is that SQL you write for one database often needs small tweaks before it runs unmodified on another — these vendor-specific variations are commonly called dialects.

This isn’t a flaw so much as a natural consequence of decades of competing vendors innovating independently while trying to stay broadly compatible with the standard. The good news: the vast majority of everyday SQL — SELECT, WHERE, JOIN, GROUP BY, and so on — is identical or nearly identical everywhere. Dialect differences tend to show up around edges like pagination, string handling, and auto-generated IDs.

Common syntax differences

Operation	PostgreSQL	MySQL	SQL Server	SQLite
Limit rows returned	`LIMIT 10`	`LIMIT 10`	`TOP 10` (in the `SELECT`)	`LIMIT 10`
Standard alternative	`FETCH FIRST 10 ROWS ONLY`	`FETCH FIRST 10 ROWS ONLY` (8.0+)	`OFFSET ... FETCH NEXT 10 ROWS ONLY`	not supported
String concatenation	`'a' \|\| 'b'`	`CONCAT('a', 'b')`	`'a' + 'b'`	`'a' \|\| 'b'`
Auto-incrementing ID	`SERIAL` / `GENERATED ALWAYS AS IDENTITY`	`AUTO_INCREMENT`	`IDENTITY(1,1)`	`INTEGER PRIMARY KEY` (autoincrements implicitly)

Seeing it in code

Limiting results: PostgreSQL / MySQL / SQLite vs SQL Server

SQL

-- PostgreSQL, MySQL, SQLite
SELECT name FROM employees ORDER BY salary DESC LIMIT 5;

-- SQL Server
SELECT TOP 5 name FROM employees ORDER BY salary DESC;

Creating an auto-incrementing primary key

SQL

-- PostgreSQL
CREATE TABLE employees (
  id SERIAL PRIMARY KEY,
  name VARCHAR(100)
);

-- MySQL
CREATE TABLE employees (
  id INT AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(100)
);

-- SQL Server
CREATE TABLE employees (
  id INT IDENTITY(1,1) PRIMARY KEY,
  name VARCHAR(100)
);

Why this matters early on

Reading someone else's SQL (a tutorial, Stack Overflow answer, or coworker's query) that doesn't run for you might just be a dialect mismatch, not a mistake
Portable, standards-leaning SQL is easier to migrate between databases later
Knowing which parts of your SQL are "standard" versus "vendor-specific" helps you predict what will and won't transfer when you switch databases or roles

Tip

This tutorial series primarily teaches standard, **PostgreSQL-flavored SQL**, since PostgreSQL sticks close to the ANSI standard and is widely used. Wherever a meaningful dialect difference exists — especially for MySQL and SQL Server — we’ll call it out explicitly so you’re not caught off guard switching databases.