Functions and Other Constructs

SemQL support in expressions and conditions built-in or customized functions that return a value.

Functions differ from comparison operators as they return a non-boolean value. They cannot be used as is in conditions unless used with a comparison operator. For example, TO_CHAR(IsValidCustomer) is a valid expression, but not a valid condition. TO_CHAR(IsValidCustomer)='1' is a valid condition.

Built-in Functions

The functions available in Semarchy xDM include functions in the following categories:

  • Strings

  • Comparison

  • Conversion

  • Date & Time

  • Matching

  • Miscellaneous

  • Null Management

  • Numeric

The complete set of built-in functions with their description is available in SemQL functions list.

When you use a function, Semarchy xDM executes it with the connection information of the data location’s datasource:

  • For Oracle, the function is looked for in the default schema accessed by this connection. If the function that does not exist in that schema, then the public synonym for the function is used.

  • For PostgreSQL, the function is looked for in the search path of the user configured for the JNDI datasource. This will determine where the function is called from.

  • For SQL Server, a function called in SemQL is automatically prefixed with dbo.

Useful and Noteworthy Functions

The following list contains noteworthy functions and expressions:

  • TO_CHAR, TO_DATE, TO_NUMBER functions to perform conversion across data types.

  • TRIM, LTRIM, RTRIM, PAD LPAD, RPAD to trip or pad with blanks.

  • SUBSTR to retrieve a part of a string.

  • REPLACE, REGEXP_REPLACE to replace part of a strings.

  • INSTR to find the location of a substring in a string.

  • NULLIF, COALESCE and NVL to handle null values.

  • GREATEST and LEAST to return the greatest and least of a list of expressions.

  • SYSDATE to retrieve the system date.

Combining functions to extract a substring (PostgreSQL)

You have a StoreLocation attribute containing values such as '5433 - Midtown'. To extract the 'Midtown' StoreName, use the following function combination in an enricher:

SUBSTR(StoreLocation, STRPOS(StoreLocation, ' - ') + 3)

Functions for Matching

Certain functions are key in a fuzzy matching process.

Functions for normalizing of transforming values to reduce the noise during fuzzy matching:

  • UPPER, LOWER and INITCAP absorb the case-sensitivity differences in strings.

  • SOUNDEX, METAPHONE and DMETAPHONE return phonetic representations (phonetization) of strings, absorbing typos.

  • SEM_NORMALIZE returns a string with non-ASCII characters transformed to ASCII-equivalent or a blank.

Soundex is not recommended as a general purpose method for phonetizing strings. Phonetization methods such as CAVERPHONE or METAPHONE for person names and METAPHONE or REFINEDSOUNDEX for organization names give better results for matching. These methods are available as functions for certain databases, and in the Text Normalization and Transliteration plug-in.

Functions that implement fuzzy matching capabilities:

  • SEM_EDIT_DISTANCE and SEM_EDIT_DISTANCE_SIMILARITY respectively returns the distance and percentage of similarity between two strings according to the Levenshtein distance algorithm.

  • SEM_JARO_WINKLER and SEM_JARO_WINKLER_SIMILARITY respectively return the distance and percentage of similarity between two strings according to the Jaro-Winkler distance algorithm.

  • SEM_NGRAMS_SIMILARITY returns the percentage of similarity of two strings according to the Dice’s coefficient similarity measure applied to the n-grams of the strings.

The *_SIMILARITY functions return a value between 0 (no match) and 100 (perfect match). If one or both strings are null, the returned value is 0.

With Oracle and PostgreSQL data locations, matching functions rely on database native capabilities. For SQL Server, matching functions rely Transact-SQL implementations, which do not provide the same performances as native capabilities.

For large data volumes, it is recommended to use third-party common language runtime (CLR) implementations of these functions for better performances. For example the Fastenshtein implementation of the Levenshtein algorithm. These functions must be installed in the SQL Server instance, and then declared/used as custom functions.

Custom Functions

SemQL allows you to use custom database functions implemented in the database instance hosting the hub.

You must declare these functions in the model to have them appear in the list of functions. See Database Functions and Procedures for more information about declaring customized functions.

Functions that are not declared can still be used in SemQL, but will not be recognized by the SemQL parser and will cause validation warnings.

Call these functions as regular functions by prefixing them with their schema and (optionnally) their package name: <schema>.<package>.<function>.

Call a CUSTFUNC() function, stored in a CUST001 package, in a COMMON_TOOLS schema
The database user of the schema hosting the hub must have sufficient privileges to execute the customized functions.

Database functions process data with the database engine. For certain processing involving for example algorithms, libraries or services not easily implemented with the database capabilities, it is preferable to opt for the Java plug-in or REST client option.

Other Constructs

CASE Expression

The CASE expression selects a result from one or more alternatives, and returns this result.

This syntax returns the first result for which the expression matches the selector. If none match, it returns the default result.

CASE selector
    WHEN expression_1 THEN result_1
    WHEN expression_n THEN result_n
    [ELSE default_result]

This syntax returns the first result for which the condition is true. If none is true, it returns the default result.

    WHEN condition_1 THEN result_1
    WHEN condition_n THEN result_n
    [ELSE default_result]
Enricher expression to transform the CustomerName attribute according to the Publisher of the record.
CASE PublisherID
    WHEN 'CRM' THEN Upper(CustomerName)
    WHEN 'MKT' THEN Upper(Replace(CustomerName, '-', ' '))
    ELSE CustomerName
The same as above, with the second syntax.
    WHEN PublisherID='CRM' THEN Upper(CustomerName)
    WHEN PublisherID='MKT' THEN Upper(Replace(CustomerName, '-', ' '))
    ELSE CustomerName

Table Functions

SemQL supports searching for an expression’s value in the values returned by a table function, using the following syntax:

expression IN table_function(parameter_1, parameter_2 ...)
The following condition uses a table function named SEARCH_FOR_IDS that returns a list of IDs from a customer name.