Column Name as Variable in PostgreSql Query

i was trying to update a table row by row in postgresql using python.

the code used was

cursor.execute("UPDATE im_entry.pr_table 
                   SET selected_entry = im_entry.usr_table.",entryn," 
                  FROM im_entry.usr_table 
                 WHERE im_entry.pr_table.image_1d = ",idn,"")

...where entryn and idn are two string variables ( entry1,entry2.. id1,id2..etc)

I am getting an error

TypeError: function takes at most 3 arguments (5 given)

My table is

image_1d | entry1 | entry2 | entry3 | entry4 | entry5 
----------+--------+--------+--------+--------+--------

How can I s开发者_开发技巧olve this?

Try:

cursor.execute(
    '''UPDATE im_entry.pr_table 
       SET selected_entry  = im_entry.usr_table.{0}
       FROM im_entry.usr_table 
       WHERE im_entry.pr_table.image_1d = ?'''.format(entryn),[idn])

Normally, you would want to call cursor.execute(sql,args), where sql is a parametrized sql query, and args is a list or tuple of values to be substituted for the parameter placeholders.

For Postgresql, the usual db driver, pyscopg, uses question marks for the parameter placeholders.

Thus, usually, you'd want to use something like

sql='''UPDATE im_entry.pr_table 
           SET selected_entry  = ?
           FROM im_entry.usr_table 
           WHERE im_entry.pr_table.image_1d = ?'''

but in your case, you aren't trying to set selected_entry to a specific value, but rather to a column name. Is that correct? In that case, you unfortunately can't use a parameter placeholder. Instead, you have to use string formatting, which is what I suggested above.

You can't bind table or column names, only the values associated with them.