October 24, 2010 Comments off

DQL is used by administrators, developers, and applications to retrieve  information from the Content Server .DQL statements operate on objects and sometimes on tables/rows while SQL statements only operate on tables/rows.

Building blocks of a DQL statement  includes,

Ø  Literals, which describes the literal formats for the Documentum datatypes

Literals are values that are interpreted by the server exactly as they are entered. Content Server recognizes .Five types of literals:

§  Integer literals

§  Floating point literals

§  Character string literals

§  ID literals

§  Date literals

Ø  Special keywords which describes the special keywords that can be used in DQL

Special keywords have special meanings for Content Server when used in a DQL query. (They cannot be used in API methods.) Some  keywords are:

§  USER, which identifies the current user

§  TRUE and FALSE, which represent the Boolean true and false.

§  DM_SESSION_DD_LOCALE, which represents the data dictionary locale.

Ø  Functions which describes the functions that can be used in DQL queries

Functions are operations on values. DQL recognizes three groups of functions and two unique functions:

  • Scalar functions: Scalar functions operate on one value and return one value.
  • Aggregate functions: Aggregate functions operate on a set of values and return  one value.
  • Date functions:Date functions operate on date values.
  • The ID function:The ID function, a unique function recognized by DQL, is used in   the FOLDER and CABINET predicates and in the IN DOCUMENT and IN ASSEMBLY clauses.
  • The MFILE_URL function:The MFILE_URL function returns URLs to content files and   renditions in particular format

Ø  Predicates  which describes the predicates that can be used in expressions in queries

Predicates are used in WHERE clauses to restrict the objects returned by a query. The WHERE clause          defines criteria that each object must meet. Predicates are the verbs within the expression that define the        criteria.

DQL recognizes these predicates:

Arithmetic operators

Comparison operators

Column and attribute predicates

SysObject predicates

Ø  Logical operators describes the logical operators supported by DQL

Logical operators are used in WHERE clauses. DQL recognizes three logical operators:

  • AND
  • OR
  • NOT

Any number of expressions can be joined together with logical operators. Content Server imposes no limit. (Underlying RDBMS may impose a limit.) The  resulting complex expression is evaluated from left to right in the order of precedence of the operators. This order, from highest to lowest, is: NOT,AND,OR

Ø  DQL reserved words which is a  list of the words reserved in DQL

DQL reserved words should be enclosed in double quotes when using in a DQL query. some keywords are

  • ALL
Categories: DOCUMENTUM Tags: , ,
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