Page Comparison

...

EXISTS is a unary operator, which is always followed by a single operand. The single operand is an AQL identified path. This operator return boolean results: true means the data associated with the specified path exists, false otherwise. EXISTS expression is a single identified expression. The latest grammar only allows this operator in WHERE clause.It may be required as part of openEHR path in future.

The example below means retrieving the identifiers of the EHRs which do not have discharge admin entry instance:.

SELECT e/ehr_id/value
FROM EHR e CONTAINS COMPOSITION c[openEHR-EHR-COMPOSITION.administrative_encounter.v1]
     CONTAINS ADMIN_ENTRY admission[openEHR-EHR-ADMIN_ENTRY.admission.v1]
WHERE NOT EXISTS c/content[openEHR-EHR-ADMIN_ENTRY.discharge.v1]

...

SELECT c/uid/value, instruction
FROM EHR e [ehr_id/value=$ehrid] CONTAINS COMPOSITION c
     CONTAINS INSTRUCTION instruction[openEHR-EHR-INSTRUCTION.referral.v1]
WHERE EXISTS instruction/links[target='ehr://327000002/87284370-2D4B-4e3d-A3F3-F303D2F4F34B@latest_trunk_version']

These advanced operators are not yet supported by the grammar. The operator syntax is borrowed from ADL specifications. These are proposed to improve the richness and flexibility of AQL so that AQL syntax supports more complicated query scenarios.

NOT

...

NOT

NOT is a unary boolean operator and it is always followed by either a single identified expression or boolean identified expression. It returns boolean results: true means the followed expression (single or boolean expression) is false.

The example below uses NOT operator followed by a single identified expression

SELECT e/ehr_id/value
FROM EHR e CONTAINS COMPOSITION c[openEHR-EHR-COMPOSITION.administrative_encounter.v1]
     CONTAINS ADMIN_ENTRY admission[openEHR-EHR-ADMIN_ENTRY.admission.v1]
WHERE NOT EXISTS c/content[openEHR-EHR-ADMIN_ENTRY.discharge.v1]

The example below uses NOT operator followed by a boolean identified expression.

SELECT e/ehr_id/value
FROM EHR e CONTAINS COMPOSITION c[openEHR-EHR-COMPOSITION.administrative_encounter.v1]
     CONTAINS ADMIN_ENTRY admission[openEHR-EHR-ADMIN_ENTRY.admission.v1]
WHERE NOT (EXISTS c/content[openEHR-EHR-ADMIN_ENTRY.discharge.v1] AND
           e/ehr_status/subject/external_ref/namespace='CEC')

The above example is equivallent to the two expressions shown below:

SELECT e/ehr_id/value
FROM EHR e CONTAINS COMPOSITION c[openEHR-EHR-COMPOSITION.administrative_encounter.v1]
     CONTAINS ADMIN_ENTRY admission[openEHR-EHR-ADMIN_ENTRY.admission.v1]
WHERE NOT EXISTS c/content[openEHR-EHR-ADMIN_ENTRY.discharge.v1] OR
      NOT e/ehr_status/subject/external_ref/namespace='CEC'


SELECT e/ehr_id/value
FROM EHR e CONTAINS COMPOSITION c[openEHR-EHR-COMPOSITION.administrative_encounter.v1]
     CONTAINS ADMIN_ENTRY admission[openEHR-EHR-ADMIN_ENTRY.admission.v1]
WHERE NOT EXISTS c/content[openEHR-EHR-ADMIN_ENTRY.discharge.v1] OR
      e/ehr_status/subject/external_ref/namespace != 'CEC'

These advanced operators are not yet supported by the grammar. The operator syntax is borrowed from ADL specifications. These are proposed to improve the richness and flexibility of AQL so that AQL syntax supports more complicated query scenarios.

AQL identified paths

Usage

...