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Questions and Answers List

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QuestionAnswer
Entity Typething about which data is kept
ATTRIBUTEproperty of entity
INSTANCEan occurrence of an entity type
IDENTIFIERattribute that uniquely identifies an instance
• TABLE/RELATIONrepresentation of an entity
FIELD/COLUMNrepresentation of an attribute
RECORD/ROWrepresents an instance
KEYrepresents an identifier
Relationshipjoins tables
Field valueassigned to a field
Data typekind of data stored in field
Foreign key –key from one table added to second table to create relationship
Databasean organized collection of data
Database Management Systems (DBMS) Ia software system that stores, manages, and facilitates access to one or more databases. E.g. Oracle, MS Access, SQL Server, SQLite, mySQL PostgreSQL
Schemacollection of objects in a database e.g. tables, views, indexes
JOINto select data from more than one table vvvv
Benefits of Relational Data BaseReduces data duplication ,Improves integrity ,Facilitates querying Facilitates access contro
create databaseCREATE DATABASE dbasename CREATE TABLE tablename ( Col1 type col2 type … ); *Constraints may be added to columns e.g. PRIMARY KEY, CHECK, FOREIGN KE
Drop DatabaseDROP DATABASE dbasename; DROP TABLE tablename;
AlterALTER TABLE tablename ADD col type; DROP COLUMN colname ; MODIFY COLUMN colname type;
Insert intoINSERT INTO tablename (col1, col2, col3, …) VALUES (v1, v2, V3, …), (v1, v2, v3, …), (V1, V2, V3, …), …;
Database updateUPDATE tablename SET col = value WHERE rowfilter; *Note the omitting the WHERE clause will cause all rows to be updated
SelectSELECT col1, col2, col3, expr1, … FROM tablename WHERE rowfilter ORDER BY column LIMIT count OFFSET offset GROUP BY column HAViNG groupfilter; -SELECT * to select all columns WHERE, ORDER BY, LIMIT, GROUP BY, HAVING are all optional clauses
DeleteDELETE FROM tablename WHERE rowfilter;
Table JoinsCross Inner / Natural Outer( Left Right Full)