I'm trying to debug a SQL statement generated with sqlite3 python module...
c.execute("SELECT * FROM %s WHERE :column = :value" % Photo.DB_TABLE_NAME, {"column": column, "value": value})
It is returning no rows when I do a fetchall()
When I run this directly on the database
SELECT * FROM photos WHERE album_id = 10
I get the expected results.
Is there a way to see the constructed query to see what the issue is?
To actually answer your question, you can use the set_trace_callback of the connection object to attach the print function; this will make all queries get printed when they are executed. Here is an example in action:
# Import and connect to database
import sqlite3
conn = sqlite3.connect('example.db')
# This attaches the tracer
conn.set_trace_callback(print)
# Get the cursor, execute some statement as an example
c = conn.cursor()
c.execute("CREATE TABLE stocks (symbol text)")
t = ('RHAT',)
c.execute("INSERT INTO stocks VALUES (?)", t)
c.execute('SELECT * FROM stocks WHERE symbol=?', t)
print(c.fetchone())
This produces the output:
CREATE TABLE stocks (symbol text)
BEGIN
INSERT INTO stocks VALUES ('RHAT')
SELECT * FROM stocks WHERE symbol='RHAT'
('RHAT',)
conn.set_trace_callback(print) is the key line here, works with sqlite3 flawlessly.
INSERT INTO stocks VALUES (?).
the problem here is that the string values are automatically embraced with single quotes. You can not dynamically insert column names that way.
Concerning your question, I'm not sure about sqlite3, but in MySQLdb you can get the final query as something like (I am currently not at a computer to check):
statement % conn.literal(query_params)
You can only use substitution parameters for row values, not column or table names.
Thus, the :column in SELECT * FROM %s WHERE :column = :value is not allowed.
