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An Introduction to SQL

An Introduction to SQL

As its name implies, SQL is used to express a database query. SQL has facilities for defining which fields should be returned from the query, if and how the query should be filtered and sorted, and so on. Although SQL is an industry standard language, various specific versions and editions of the standard are implemented by SQL-based databases. Crystal Reports does not use just a single syntax, but rather is robust enough to handle most major SQL language derivations. The rest of this appendix walks you through the SQL Language and points out specific areas that are of concern to Crystal Reports. Although it doesn't focus on a specific version of SQL, it does point out differences where appropriate.

The SELECT Statement

Even though the name implies that SQL is only about querying databases, most implementations also enable you to insert, delete, and update records inside the database. Each of these distinct actions has its own command: SELECT (query), INSERT, UPDATE, and DELETE. Although SQL commands allow any valid SQL statement that returns records to be used, SELECT statements are generally the only statements to be used. However, there are situations in which other statements can be used in addition to a SELECT statement. One example of this is running an INSERT statement to create a record to log the fact that the report is being run. This section focuses on describing the SELECT statement from SQL.


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