04_SQL1.pdf - CITS1402 Relational Database Management...

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CITS1402 Relational Database Management Systems Video 04 — SQL I Gordon Royle Department of Mathematics & Statistics
Structured Query Language Structured Query Language , or SQL, is the standard computer language used to interact with a relational database. I A user connects to a DB, usually containing several tables I The user writes a SQL query , which is a declarative statement giving the logical description of a new table I The RDBMS optimises the query, runs it, and produces a relational table containing the output I The SQL query may, or may not, alter the existing tables “Tables in, tables out — everything is a table”
Structured Query Language Structured Query Language or SQL is just an ISO standard specifying the syntax and semantics of a declarative language for accessing a relational database. I Syntax — The syntax determines which statements are legal expressions in the language I Semantics — The semantics determine the meaning of each of the legal expressions
Many variants There is no compulsion on any database vendor to stick precisely

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