lect8 - 1.264 Lecture 8 SQL: Basics, SELECT SQL Structured...

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1.264 Lecture 8 SQL: Basics, SELECT
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SQL Structured query language (SQL) used for Data definition (DDL): tables and views (virtual tables) Data manipulation (DML): user or program can INSERT, DELETE, UPDATE or retrieve (SELECT) data Access control: security Data sharing: by concurrent users Data integrity: referential integrity and transactions Not a complete language like Java, Visual Basic or C++ SQL is sub-language of about 30 statements Usually embedded in another language or tool for database access SQL has several inconsistencies; NULLs are problematic Portable across operating systems and somewhat among vendors
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Things that vary among SQL implementations Error codes Data types supported (dates/times, currency, string variations) System tables, about the structure of the database itself Interactive SQL Programming interface: no vendor follows the standard Dynamic SQL, used for report writers and query tools Implementer-defined variations within the standard Database initialization, opening and connection
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SQL SELECT SELECT constructed of clauses to get columns and rows from one or more tables or views. Clauses must be in order: SELECT columns INTO new table FROM table or view WHERE specific rows or a join is created GROUP BY grouping conditions (columns) HAVING group-property (specific rows) ORDER BY ordering criterion ASC | DESC
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lect8 - 1.264 Lecture 8 SQL: Basics, SELECT SQL Structured...

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