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ehrQL examples

How to use this page🔗

You can either read this page from start to end to get an idea of the kinds of queries you can make with ehrQL.

Or you can use the navigation bar at the top-right of this page, to see a list of the examples, and then jump to a specific example of interest.

Examples in this page all use the TPP backend🔗

🚧 For consistency throughout the examples, and to make it possible to use backend-specific tables in addition to core tables, the example dataset definitions here all use the TPP backend.

Some examples use codelist_from_csv()🔗

🚧 This guidance should be improved in future.

âš  Some examples refer to CSV codelists using the codelist_from_csv function, but are incomplete. To actually use these code example, you will need to correctly complete the function call. The codelists are not provided as a part of these examples.

For example, instead of:

asthma_codelist = codelist_from_csv(XXX)

you will need a line more like:

asthma_codelist = codelist_from_csv("your-asthma-codelist.csv", column="code")

which provides the filename your-asthma-codelist.csv and the name of the CSV column with codes.

🗒 It is also possible to use a category column with codelist_from_csv(). Until this documentation is improved, refer to the ehrQL source code.

Finding patient demographics🔗

Finding each patient's age🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import patients

dataset = Dataset()
dataset.age = patients.age_on("2023-01-01")

Alternatively, using a native Python date:

from datetime import date
from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import patients

dataset = Dataset()
dataset.age = patients.age_on(date(2023, 1, 1))

Or using an index_date variable:

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import patients

index_date = "2023-01-01"
dataset = Dataset()
dataset.age = patients.age_on(index_date)

Assigning each patient an age band🔗

from databuilder.ehrql import Dataset, case, when
from databuilder.tables.beta.tpp import patients

dataset = Dataset()
age = patients.age_on("2023-01-01")
dataset.age_band = case(
        when(age < 20).then("0-19"),
        when(age < 40).then("20-39"),
        when(age < 60).then("40-59"),
        when(age < 80).then("60-79"),
        when(age >= 80).then("80+"),
        default="missing",
)

Finding each patient's date of birth🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import patients

dataset = Dataset()
dataset.date_of_birth = patients.date_of_birth

Finding each patient's date of death in their primary care record🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import patients

dataset = Dataset()
dataset.date_of_death = patients.date_of_death

🗒 This value comes from the patient's EHR record.

There is generally a lag between the death being recorded in ONS data and appearing in the primary care record, but the date itself is usually reliable when it appears. By contrast, cause of death is often not accurate in the primary care record so we don't make it available to query here.

Finding each patient's date, place, and cause of death from ONS records🔗

from databuilder.ehql import Dataset
from databuilder.tables.beta.tpp import ons_deaths

dataset = Dataset()
dataset.date_of_death = ons_deaths.date
dataset.place_of_death = ons_deaths.place
dataset.cause_of_death = ons_deaths.cause_of_death_01

🗒 There are currently multiple cause of death fields. We aim to resolve these to a single feature in the future.

Finding each patient's sex🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import patients

dataset = Dataset()
dataset.sex = patients.sex

The possible values are "female", "male", "intersex", and "unknown".

Finding each patient's ethnicity🔗

🚧 This is more complicated and will be added in future.

Finding each patient's IMD rank🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import addresses

dataset = Dataset()
dataset.imd = addresses.for_patient_on("2023-01-01").imd_rounded

The original IMD ranking is rounded to the nearest 100. The rounded IMD ranking ranges from 0 to 32,800.

See this code comment about how we choose one address if a patient has multiple registered addresses on the given date.

Calculating each patient's IMD quintile🔗

from databuilder.ehrql import Dataset, case, when
from databuilder.tables.beta.tpp import addresses

dataset = Dataset()
imd = addresses.for_patient_on("2023-01-01").imd_rounded
dataset.imd_band = case(
        when(imd < 32844 * 1 / 5).then("1 (most deprived)"),
        when(imd < 32844 * 2 / 5).then("2"),
        when(imd < 32844 * 3 / 5).then("3"),
        when(imd < 32844 * 4 / 5).then("4"),
        when(imd < 32844 * 5 / 5).then("5 (least deprived)"),
        default="unknown"
)

Finding each patient's rural/urban classification🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import addresses

dataset = Dataset()
dataset.rural_urban = addresses.for_patient_on("2023-01-01").rural_urban_classification

The meaning of this value is as follows:

  • 1 - Urban major conurbation
  • 2 - Urban minor conurbation
  • 3 - Urban city and town
  • 4 - Urban city and town in a sparse setting
  • 5 - Rural town and fringe
  • 6 - Rural town and fringe in a sparse setting
  • 7 - Rural village and dispersed
  • 8 - Rural village and dispersed in a sparse setting

Finding each patient's MSOA🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import addresses

dataset = Dataset()
dataset.msoa = addresses.for_patient_on("2023-01-01").msoa

Finding multiple attributes of each patient's address🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import addresses

dataset = Dataset()
address = addresses.for_patient_on("2023-01-01")
dataset.imd = address.imd
dataset.rural_urban_classification = address.rural_urban_classification
dataset.msoa = address.msoa

Finding each patient's practice's pseudonymised identifier🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import practice_registrations

dataset = Dataset()
dataset.practice = practice_registrations.for_patient_on("2023-01-01").practice_pseudo_id

Finding each patient's practice's STP🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import practice_registrations

dataset = Dataset()
dataset.stp = practice_registrations.for_patient_on("2023-01-01").practice_stp

Finding each patient's practice's region🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import practice_registrations

dataset = Dataset()
dataset.region = practice_registrations.for_patient_on("2023-01-01").nuts1_region_name

Finding multiple attributes of each patient's practice🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import practice_registrations

dataset = Dataset()
registration = practice_registrations.for_patient_on("2023-01-01")
dataset.practice = registration.practice_pseudo_id
dataset.stp = registration.practice_stp
dataset.region = registration.nuts1_region_name

Does each patient have an event matching some criteria?🔗

Does each patient have a clinical event matching a code in a codelist?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.has_had_asthma_diagnosis = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).exists_for_patient()

Does each patient have a clinical event matching a code in a codelist in a time period?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.has_recent_asthma_diagnosis = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_between("2022-07-01", "2023-01-01")
).exists_for_patient()

Does each patient have a medication event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import medications

statin_medications = codelist_from_csv(XXX)

dataset = Dataset()
dataset.has_recent_statin_prescription = medications.where(
        medications.dmd_code.is_in(statin_medications)
).where(
        medications.is_on_or_between("2022-07-01", "2023-01-01")
).exists_for_patient()

Does each patient have a hospitalisation event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import hospital_admissions

cardiac_diagnosis_codes = codelist_from_csv(XXX)

dataset = Dataset()
dataset.has_recent_cardiac_admission = hospital_admissions.where(
        hospital_admissions.primary_diagnoses .is_in(cardiac_diagnosis_codes)
).where(
        hospital_admissions.is_on_or_between("2022-07-01", "2023-01-01")
).exists_for_patient()

How many events does each patient have matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import medications

statin_medications = codelist_from_csv(XXX)

dataset = Dataset()
dataset.number_of_statin_prescriptions_in_last_year = medications.where(
        medications.dmd_code.is_in(statin_medications)
).where(
        medications.is_on_or_between("2022-01-01", "2023-01-01")
).count_for_patient()

What is the first/last event matching some criteria?🔗

The first_for_patient() and last_for_patient() methods can only be used on a sorted frame. Frames can be sorted by calling the sort_by() method with the column to sort the frame by.

What is the earliest/latest clinical event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.first_asthma_diagnosis_date = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).sort_by(
        clinical_events.date
).first_for_patient().date

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.last_asthma_diagnosis_date = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).sort_by(
        clinical_events.date
).last_for_patient().date

What is the earliest/latest medication event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import medications

statin_medications = codelist_from_csv(XXX)

dataset = Dataset()
dataset.first_statin_prescription_date = medications.where(
        medications.dmd_code.is_in(statin_medications)
).where(
        medications.date.is_on_or_after("2022-07-01")
).sort_by(
        medications.date
).first_for_patient().date

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import medications

statin_medications = codelist_from_csv(XXX)

dataset = Dataset()
dataset.last_statin_prescription_date = medications.where(
        medications.dmd_code.is_in(statin_medications)
).where(
        medications.date.is_on_or_after("2022-07-01")
).sort_by(
        medications.date
).last_for_patient().date

What is the earliest/latest hospitalisation event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import hospital_admissions

cardiac_diagnosis_codes = codelist_from_csv(XXX)

dataset = Dataset()
dataset.first_cardiac_hospitalisation_date = hospital_admissions.where(
        hospital_admissions.snomedct_code.is_in(cardiac_diagnosis_codes)
).where(
        hospital_admissions.date.is_on_or_after("2022-07-01")
).sort_by(
        hospital_admissions.date
).first_for_patient().date

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import medications

cardiac_diagnosis_codes = codelist_from_csv(XXX)

dataset = Dataset()
dataset.last_cardiac_hospitalisation_date = medications.where(
        medications.dmd_code.is_in(cardiac_diagnosis_codes)
).where(
        medications.date.is_on_or_after("2022-07-01")
).sort_by(
        medications.date
).last_for_patient().date

What is the clinical event, matching some criteria, with the least/greatest value?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

hba1c_codelist = codelist_from_csv(XXX)

dataset = Dataset()
max_hba1c = clinical_events.where(
        clinical_events.snomedct_code.is_in(hba1c_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).numeric_value.maximum_for_patient()

dataset.date_of_max_hba1c_observed = clinical_events.where(clinical_events.snomedct_code.is_in(hba1c_codelist)
).where(
        clinical_events.numeric_value == max_hba1c
).sort_by(
        clinical_events.date
).last_for_patient().date

Getting properties of an event matching some criteria🔗

What is the code of the first/last clinical event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.first_asthma_diagnosis_date = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).sort_by(
        clinical_events.date
).first_for_patient().snomedct_code

What is the date of the first/last clinical event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.first_asthma_diagnosis_date = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).sort_by(
        clinical_events.date
).first_for_patient().date

What is the code and date of the first/last clinical event matching some criteria?🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
first_asthma_diagnosis = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).sort_by(
        clinical_events.date
).first_for_patient()
dataset.first_asthma_diagnosis_code = first_asthma_diagnosis.snomedct_code
dataset.first_asthma_diagnosis_date = first_asthma_diagnosis.date

Finding events occuring close in time to another event🔗

Finding the code of the first medication after the first clinical event matching some criteria🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.query_language import weeks
from databuilder.tables.beta.tpp import clinical_events, medications

asthma_codelist = codelist_from_csv(XXX)
inhaled_corticosteroid_codelist = codelist_from_csv(XXX)

dataset = Dataset()
first_asthma_diagnosis_date = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).sort_by(
        clinical_events.date
).first_for_patient().date
dataset.first_asthma_diagnosis_date = first_asthma_diagnosis_date
dataset.count_ics_prescriptions_2wks_post_diagnosis = medications.where(
        medications.dmd_code.isin(inhaled_corticosteroid_codelist
).where(
        medications.date.is_on_or_between(first_asthma_diagnosis_date,first_asthma_diagnosis_date + weeks(2))
)

Performing arithmetic on numeric values of clinical events🔗

Finding the mean observed value of clinical events matching some criteria🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

hba1c_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.mean_hba1c = clinical_events.where(
        clinical_events.snomedct_code.is_in(hba1c_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).numeric_value.mean_for_patient()

Finding the observed value of clinical events matching some criteria expressed relative to another value🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

hba1c_codelist = codelist_from_csv(XXX)

dataset = Dataset()
mean_hba1c = clinical_events.where(
        clinical_events.snomedct_code.is_in(hba1c_codelist)
).where(
        clinical_events.date.is_on_or_after("2022-07-01")
).numeric_value.maximum_for_patient()

dataset.mean_max_hbac_difference = max_hba1c - (
clinical_events.where(clinical_events.snomedct_code.is_in(hba1c_codelist)
).where(
        clinical_events.numeric_value == max_hba1c
).sort_by(
        clinical_events.date
).numeric_value.mean_for_patient())

Finding events within a date range🔗

Finding events within a fixed date range🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.has_recent_asthma_diagnosis = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_between("2022-07-01", "2023-01-01")
).exists_for_patient()

Finding events within a date range plus a constant🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.query_language import weeks
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

index_date = "2022-07-01"

dataset = Dataset()
dataset.has_recent_asthma_diagnosis = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date.is_on_or_between(index_date, index_date + weeks(2))
).exists_for_patient()

Finding events within a dynamic date range🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.query_language import months
from databuilder.tables.beta.tpp import clinical_events

diabetes_codelist = codelist_from_csv(XXX)
hba1c_codelist = codelist_from_csv(XXX)

dataset = Dataset()
first_diabetes_code_date = clinical_events.where(
        clinical_events.snomedct_code.is_in(diabetes_codelist)
).sort_by(
        clinical_events.date
).first_for_patient().date

dataset.count_of_hba1c_tests_6mo_post_first_diabetes_code = clinical_events.where(
        clinical_events.snomedct_code.is_in(hba1c_codelist)
).where(
        clinical_events.date.is_on_or_between(first_diabetes_code_date, first_diabetes_code_date + months(6))
).count_for_patient()

Excluding events which have happened in the future🔗

Data quality issues with many sources may result in events apparently happening in future dates (e.g. 9999-01-01), it is useful to filter these from your analysis.

from datetime import date
from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.has_recent_asthma_diagnosis = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).where(
        clinical_events.date > "2022-07-01"
).where(
        clinical_events.date < datetime.today()
).exists_for_patient()

Extracting parts of dates and date differences🔗

Finding the year an event occurred🔗

from datetime import date
from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)

dataset = Dataset()
dataset.year_of_first = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).sort_by(
        clinical_events.date
).first_for_patient().date.year

Finding prescriptions made in particular months of the year🔗

from databuilder.ehrql import Dataset
from databuilder.tables.beta.tpp import medications

amoxicillin_codelist = codelist_from_csv(XXX)

winter_months = [10,11,12,1,2,3]

dataset = Dataset()
dataset.winter_amoxicillin_count = medications.where(
        medications.dmd_code.isin(amoxicillin_codelist)
).where(
        medications.date.month.isin(winter_months)
)

Finding the number of weeks between two events🔗

from databuilder.ehrql import Dataset, codelist_from_csv
from databuilder.tables.beta.tpp import clinical_events

asthma_codelist = codelist_from_csv(XXX)
asthma_review_codelist = codelist_from_csv(XXX)

dataset = Dataset()
first_asthma_diagnosis = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_codelist)
).sort_by(clinical_events.date).first_for_patient()

first_asthma_review = clinical_events.where(
        clinical_events.snomedct_code.is_in(asthma_review_codelist)
).where(
        clinical_events.date.is_on_or_after(first_asthma_diagnosis)
).sort_by(clinical_events.date).first_for_patient()

dataset.weeks_between_diagnosis_and_review = (first_asthma_review - first_asthma_diagnosis).weeks