遍历列表 Python SQL

Question

I'm trying to search a database, by iterating through a list of search values. I'm almost there as this works for integers but not strings. The code below won't work, but if I replace the list values with numbers it does:

mycursor = mydb.cursor()

lst = []

select_query = "SELECT * FROM fruit WHERE content LIKE "
ids = ["apple", "pear"]

for x in ids:
    var = select_query + str(x)
    
    mycursor.execute(var)
    lst.extend(mycursor.fetchall())

print(lst)

Answer 1

It's because you have to enclose strings in quotation marks in SQL. So for example

SELECT * FROM fruit WHERE content LIKE 'pears'

will work, and it will only work with the single quotations around "pears". Even better, type conversion can (and should) be done automatically with psycopg2:

select_query = "SELECT * FROM fruit WHERE content LIKE %s"
...
mycursor.execute(select_query, (x,))

https://www.psycopg.org/docs/usage.html#strings-adaptation