Expression

Expression is a combination of one or more values, operators and SQL functions that results in to a value. These expressions are similar to a formula and they are written in query language. You can also use them to query the database for a specific set of data.

Expression check validate the SQL expression to identify the data in base table column matches with the expression. the failed values will flag as a data quality issue

SQL expression must be compliant with the target database / warehouse

For example, If the base table is LINEITEM, base column is L_SHIPMODE, then the expression check is defined as,
(not exists (select L_SHIPMODE from LINEITEM where substr(NVL(L_SHIPMODE,’X’),1,3)=’AIR’))

Here, if the LINEITEM.L_SHIPMODE column value does not match with specified expression check then those base table records are considered as invalid.

Steps to create expression check rule in uArrow:

1. Click + Add button in the expression check rule for column L_SHIPMODE.

2. Do the following, In the expression section for rule.

Parameter Name	Description
Column	Choose the expression column.
Rule Description	Specify the rule description.
Rule Category	Choose or create new dimension to classify rule if required
Sql Expression	Fill the relevant database SQL expression.

Below is the sample screen with sql expression values populated for expression check.

* Click Verify button to validate SQL expression.

* Click Apply button to update sql expression changes, and click save button to save job.