Crestron CT-3000 Specifikace stáhnout pdf (Strana 35)

Crestron e-control Database Manager SW-DBM

35 •• The Database File Installation & Reference Guide — DOC. 5823

T.Minutes AS ["],

T.Seconds AS [']

FROM Albums A

INNER JOIN Tracks T

ON A.CDJID = T.CDJID

Note the following syntax features of SQL, all illustrated in the above example:

• Dot syntax. When the same field name is used in more than one table, you

must use the syntax table.field to eliminate ambiguity. In the above example,

this syntax was used throughout, although in fact the fields Artist and

Track did not actually appear in both tables.

• Table name aliases. The FROM clause assigns the alias A to the Albums

table and T to the Tracks table. Once these aliases are established, you

can use them instead of the full table names in the listFields and dataFields

columns.

• Captions. Use the word AS after a field name in the SELECT clause to

introduce a caption. In the above, ARTIST, ALBUM, CUT, etc. are

captions. Unlike a table name alias, you cannot refer to the field using its

caption. Captions, when defined, are displayed in place of the field name in

reports generated with Microsoft Access. The server also uses captions during

successive queries. The captions are inserted as data into the description string

and transmitted to the control system via the QueryDescription signal. If the

caption is not defined here, the field name is used instead.

• Square brackets are used around any table names, field names, and captions

that contain spaces or punctuation.

Outer joins are also supported. A LEFT JOIN includes all rows from the first table in

the output, even if it has no matching rows in the second table. A RIGHT JOIN

includes all rows from the second table even if it has no matching rows in the first

table. With an outer join, matching rows are still matched and the selected columns

from the two tables are strung together in one record. Any row that is included that

does not have a matching row in the other table is assigned default values for the

additional columns – zero for numeric columns and blank for character columns.

The Queries Table

You do not need to know SQL or Microsoft Access to construct a query for use by

the scroller signal blocks in the Crestron Software Server. In the server application,

you construct queries using a special database table named Queries.

This requires that each database you create contain at least two tables, the table with

the data for your application and a Queries table. For example, the Address Book

database contains two tables, Addresses and Queries:

The database window from Microsoft Access, showing the two tables in the AddrBook database..

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Crestron CT-3000 Specifikace Strana 35