关于ANSI的两项技术疑问：ANSI与SQL关系是否类同POSIX与Unix？SQL是否为ANSI标准？

Great questions—let’s break these down clearly, since the relationship between standards and the technologies they govern can get a bit fuzzy.

1. Is the relationship between ANSI and SQL the same as POSIX and Unix? #

Yes, this analogy holds up really well, though there are a few minor nuances to note:

• Both pairs represent a standardization body defining a specification for a widely adopted, originally fragmented technology:
  • Unix started as AT&T's proprietary OS, with dozens of incompatible variants (BSD, System V, etc.) popping up. POSIX (initially developed by IEEE, later adopted as an ANSI standard) created a common set of interfaces and behaviors to ensure compatibility across Unix-like systems.
  • SQL began as IBM's SEQUEL language for its System R database. As other vendors built their own databases with similar query languages (each with their own quirks), ANSI stepped in to create a standardized version of SQL to promote interoperability between different database systems.
• The key similarity: In both cases, the standard (ANSI SQL, POSIX) acts as a baseline. Vendors can build implementations that adhere to the standard while adding proprietary extensions (like PostgreSQL's COPY command or Linux-specific POSIX enhancements) to differentiate their products.

The only small difference is that POSIX is more focused on system interfaces and behavior, while ANSI SQL is focused on a programming/query language syntax and semantics—but the core "standardizing a fragmented ecosystem" dynamic is identical.

2. Is SQL an ANSI standard? #

Absolutely, though it’s important to clarify what that means in practice:

• ANSI first published a standardized version of SQL in 1986 (officially called ANSI X3.135-1986), often shorthanded as SQL-86. Since then, ANSI has collaborated with ISO to update the standard regularly—you’ll see references to versions like SQL-92, SQL:2003, SQL:2016, and the latest SQL:2023.
• That said, not all SQL you’ll use day-to-day is strictly ANSI-compliant. Most database vendors (MySQL, PostgreSQL, Oracle, SQL Server) implement the core ANSI SQL specification but add their own proprietary extensions (like T-SQL for SQL Server, PL/pgSQL for PostgreSQL) that aren’t part of the standard. These extensions let vendors offer unique features, but they can make writing cross-database SQL tricky.
• So to sum up: The foundational SQL language is defined by an ANSI (and ISO) standard, but real-world SQL implementations often include non-standard additions tailored to specific database systems.

内容的提问来源于stack exchange，提问作者elbarna