Query-By-Example (QBE) [68]

QBE

• Query-by-Example

• Graphical User Interface (GUI)

• specify query in a table format
• itemize

VDB

• VISUAL DB is an extended version of QBE

• written in Tcl/Tk

• table format

• buttons for relational algebra

• ( $\pi,\sigma,\delta,\Join,\times,-,\div,\cup,\cap$)

• calls Shell SQL (sql_project, sql_restrict, ...)

Buttons

create, insert, rename, extend, destroy, restrict, update, delete, join, times, minus, divide, union, intersect, project, sort, sum, summarize, unique, copy, help

QBE: Project, Restrict, Join [69]

Query

Get SNAMEs with shipment QTY$>=800$.

QBE

SPJ	S#	P#	J#	QTY
	_$x$			$>=800$

S	S#	SNAME	STATUS	CITY
	_$x$	.P

Usage

• project: .P (under column names OR table name)

• restrict: $>=800$ (or "P2")

• join: _$x$ (variables)