GITTA-Logo
PDF Version of this document Search Help

Lesson Navigation IconAnfragesprache SQL

Unit Navigation IconSQL Overview

Unit Navigation IconBasic database queries

LO Navigation IconSelect-From-Where

LO Navigation IconMultiple conditions

LO Navigation IconComplex conditions

LO Navigation IconArithmetische Operatoren

LO Navigation IconNon-relational constructs

LO Navigation IconSet operators

LO Navigation IconUsage of SQL

LO Navigation IconDatabase queries

Unit Navigation IconSQL Insert, Delete and Update

Unit Navigation IconSummary

Unit Navigation IconRecommended Reading

Unit Navigation IconBibliography

Unit Navigation IconMetadata


GITTA/CartouCHe news:


Go to previous page Go to next page

Complex conditions

Nested queries

Conditions are usually made of an attribute, a value and an operator that forms the condition (eg. Name="John"). But the values themselves don't have to be constants, they can be the result of another sub-query. We then talk about nested queries. Using the IN-operator nested queries can be as deep as necessary.

Nested queries

Comparison operators

SQL supports different comparison operators like ==,<,>,<>,<=,>=,between etc. If an operator is used to compare an attribute with a constant, we talk about restriction. If the operator is used to compare two attributes, then we talk about a join. With joins, data from different relations can be compared and combined. Of course only attributes with the same domain (value range) can be compared.

Comparison operators

If in the SELECT-clause a star (*) instead of an attribute list is used, then all attributes are displayed.

Join operators
Top Go to previous page Go to next page