May 2014 Archive

Projection in SQL

We can, if we wish, remove some of the components of the selected tuples; that is, we can project the relation created by an SQL query onto some of its attributes. In place of the * of the SELECT clause, we may list some of the attributes of the relation mentioned in the FROM

Selection in SQL

The selection operator of relational algebra, and much more, is available through the WHERE clause of SQL. The expressions that may follow WHERE contain conditional expressions like those found in common languages such as C or Java.

Comparison of Strings

Two strings are equal if they are the same sequence of characters. SQL allows declarations of different types of strings, for instance fixed-length arrays of characters and variable-length lists of characters. If so, we can expect reasonable

Tags : strings, arrays, sql
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