尝试使用 Python 检查值是否在 sqlite3 中

Question

I am trying to check if a value is in SQLite with python to then either update the table if the value exists or create a new value if it is not. I have tried to create a cursor to check rows, append the rows to a list with loop, check if value exists, check the count of the rows... I seems to get hung up on the if statement when trying to access the value initialized from the query. Here is the code:

checkT = db.execute("SELECT COUNT(*) FROM trans WHERE stock=:stock AND id=:user_id", stock=request.form.get("symbol"), user_id=session["user_id"])
if checkT > 0:
            print("there")
else:
            print("not there")

How can I fix this? Thank you!

Answer 1

From the CS50 Library for Python doc for execute

Returns

for SELECTs, a list of dict objects, each of which represents a row in the result set; for INSERTs, the primary key of a newly inserted row (or None if none); for UPDATEs, the number of rows updated; for DELETEs, the number of rows deleted; for CREATEs, True on success; on error, a RuntimeError is raised

checkT is a list with one element, which is a dict with one key/value pair.

This checkT[0]['COUNT(*)'] will give the number returned from the sql. Counting the rows would not be appropriate in this case because this query will always return one row.

One hint: column names in a SELECT can be aliased, given a different name, like so:

SELECT COUNT(*) as count from...... . It would just be typing convenience, because then the key in the returned dict will be count instead of COUNT(*) .

Remember: in the flask run terminal there is a traceback with gives more details information on the error received (assuming "hung up" means a 500 Internal Server Error).