I'm not asking for the SHOW COLUMNS
command.
I want to create an application that works similarly to heidisql, where you can specify an SQL query and when executed, returns a result set with rows and columns representing your query result. The column names in the result set should match your selected columns as defined in your SQL query.
In my Python program (using MySQLdb
) my query returns only the row and column results, but not the column names. In the following example the column names would be ext
, totalsize
, and filecount
. The SQL would eventually be external from the program.
The only way I can figure to make this work, is to write my own SQL parser logic to extract the selected column names.
Is there an easy way to get the column names for the provided SQL? Next I'll need to know how many columns does the query return?
# Python import MySQLdb #=================================================================== # connect to mysql #=================================================================== try: db = MySQLdb.connect(host="myhost", user="myuser", passwd="mypass",db="mydb") except MySQLdb.Error, e: print "Error %d: %s" % (e.args[0], e.args[1]) sys.exit (1) #=================================================================== # query select from table #=================================================================== cursor = db.cursor () cursor.execute ("""\ select ext, sum(size) as totalsize, count(*) as filecount from fileindex group by ext order by totalsize desc; """) while (1): row = cursor.fetchone () if row == None: break print "%s %s %s\n" % (row[0], row[1], row[2]) cursor.close() db.close()
SQL aliases are used to give a table, or a column in a table, a temporary name. Aliases are often used to make column names more readable. An alias only exists for the duration of that query. An alias is created with the AS keyword.
You can only use column aliases in GROUP BY, ORDER BY, or HAVING clauses. Standard SQL doesn't allow you to refer to a column alias in a WHERE clause. This restriction is imposed because when the WHERE code is executed, the column value may not yet be determined.
You can get the MySQL table columns data type with the help of “information_schema. columns”. SELECT DATA_TYPE from INFORMATION_SCHEMA. COLUMNS where table_schema = 'yourDatabaseName' and table_name = 'yourTableName'.
cursor.description will give you a tuple of tuples where [0] for each is the column header.
num_fields = len(cursor.description) field_names = [i[0] for i in cursor.description]
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