Some of the major modern dialects of SQL are:

• Oracle SQL.
• PL SQL, which is an extension of Oracle SQL.
• Microsoft SQL Server’s version, TSQL or T-SQL, which is short for Transact SQL.

None of these dialects implement the ISO or ANSI SQL language in full. There are a few reasons:

• Different vendors have different ideas for what they want
• They may need all the features of Standard SQL
• They want to incorporate their own ideas of what SQL should do

So while some vendors get fairly close, there is no implementation of the full Standard SQL. Standard SQL is more of a concept rather than an actual implemented language. Similarly, there is no such thing in the real world as “English.” Instead, there are dialects, such as British English and American English. Some institutions may attempt to regulate their English dialect. However, dialects develop as actual usage varies due to changing circumstances. This is the same with Standard SQL, which evolves every few years.

Standard SQL does not replicate exactly the standard that its creator, Cobb, came up with. For example, while set theory uses records and fields, Standard SQL uses rows and columns. So even the SQL standard is not a perfect implementation of the original SQL theory.