Query error: Column name ICUSTAY_ID is ambiguous. Using multiple subqueries in BigQuery - sql

Question

Hi, I receive the following query error "Query error: Column name ICUSTAY_ID is ambiguous" referred to the third last line of code (see the following code). Please can you help me? Thank you so much!
I am an SQL beginner..
WITH t AS
(
SELECT
*
FROM
(
SELECT *,
DATETIME_DIFF(CHARTTIME, INTIME, MINUTE) AS pi_recorded
FROM
(
SELECT
*
FROM
(
SELECT * FROM
(SELECT i.SUBJECT_ID, p.dob, i.hadm_id, p.GENDER, a.ETHNICITY, a.ADMITTIME, a.INSURANCE, i.ICUSTAY_ID,
i.DBSOURCE, i.INTIME, DATETIME_DIFF(a.ADMITTIME, p.DOB, DAY) AS age,
CASE
WHEN DATETIME_DIFF(a.ADMITTIME, p.DOB, DAY) <= 32485
THEN 'adult'
WHEN DATETIME_DIFF(a.ADMITTIME, p.DOB, DAY) > 32485
then '>89'
END AS age_group
FROM `project.mimic3.ICUSTAYS` AS i
INNER JOIN `project.mimic3.PATIENTS` AS p ON i.SUBJECT_ID = p.SUBJECT_ID
INNER JOIN `project.mimic3.ADMISSIONS` AS a ON i.HADM_ID = a.HADM_ID)
WHERE age >= 6570
) AS t1
LEFT JOIN
(
SELECT ITEMID, ICUSTAY_ID, CHARTTIME, VALUE, FROM `project.mimic3.CHARTEVENTS`
WHERE ITEMID = 551 OR ITEMID = 552 OR ITEMID = 553 OR ITEMID = 224631
OR ITEMID = 224965 OR ITEMID = 224966
) AS t2
ON t1.ICUSTAY_ID = t2.ICUSTAY_ID
)
)
WHERE ITEMID IN (552, 553, 224965, 224966) AND pi_recorded <= 1440
)
SELECT ICUSTAY_ID #### Query error: Column name ICUSTAY_ID is ambiguous
FROM t
GROUP BY ICUSTAY_ID;

Answer 1

Both t1 and t2 have a column called ICUSTAY_ID. When you join them together into a single dataset you end up with 2 columns with the same name - which obviously can't work as there would be no way of uniquely identify each column.
You need to alias these columns in you code or not include one or the other if you don't need both