Use of NULL value in Voyager Prepackaged Access Reports
- Product: Voyager
- Relevant for Installation Type: Multi-Tenant Direct, Dedicated-Direct, Local, TotalCare
Question
Use of the NULL value in Voyager Prepackaged Access Reports.
Answer
NULL is a special value that a field can have.
For text fields, it is different from blank.
For numeric fields, it is different from zero.
Blank and zero are actual values.
NULL means that the database doesn't know what the value is. In other words, no value has been assigned to the cell.
Any field can have a value of NULL.
Looking for NULL using an Access query usually requires an outer join where join on "Is Null". In such queries, Null is the value of data in a cell that’s only there because of an outer join.
One common use of this query technique is for finding items that have not circulated. An item that has not been charged has a NULL value for charge_date.
Example:
([Circulation Transactions (Charges)].CHARGE_DATE) Is Null
Another common use example is in MFHD_MASTER where the value of display_call_no is NULL when there is no 852$h.
Example:
(MFHD_MASTER.DISPLAY_CALL_NO) Is Null
NULL is not used for BLOB queries, which return string values; in those cases use "" to find empty string values.
Constructing custom SQL queries by request and troubleshooting unexpected results from customer-created SQL queries falls outside the scope of Support. The above has been posted for informational purposes. Voyager-L and Developer Network are useful resources for finding helpful custom SQL or obtaining assistance from peers in troubleshooting custom queries.
- Article last edited: 27-Apr-2020