1、Chapter 4: Introduction to SQL
① Overview of the SQL Query Language
② Data Definition
③ Basic Query Structure
④ Additional Basic Operations
⑤ Set Operations
⑥ Null Values
⑦ Aggregate Functions
⑧ Nested Subqueries
⑨ Modification of the Database
2、History
① IBM Sequel language developed as part of System R project at the IBM San Jose Research Laboratory
② Renamed Structured Query Language (SQL)
③ ANSI and ISO standard SQL:
- SQL-86, SQL-89, SQL-92
- SQL:1999, SQL:2003, SQL:2008
④ Commercial systems offer most, if not all, SQL-92 features, plus varying feature sets from later standards and special proprietary features
- Not all examples here may work one-to-one on your particular system.
3、Data Definition Language
The SQL data-definition language (DDL) allows the specification of inform
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