Databases
StackOverflow2013
Postsdbo
POHow to get a row-by-row MySQL ResultSet in python
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow to get a row-by-row MySQL ResultSet in python
    primarykey
    data
    text
    <p>MySQL ResultSets are by default retrieved completely from the server before any work can be done. In cases of huge result sets this becomes unusable. I would like instead to actually retrieve the rows one by one from the server.</p> <p>In Java, following the instructions <a href="http://dev.mysql.com/doc/refman/5.1/en/connector-j-reference-implementation-notes.html" rel="noreferrer">here</a> (under "ResultSet"), I create a statement like this:</p> <pre><code>stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE); </code></pre> <p>This works nicely in Java. My question is: is there a way to do the same in python?</p> <p>One thing I tried is to limit the query to a 1000 rows at a time, like this:</p> <pre><code>start_row = 0 while True: cursor = conn.cursor() cursor.execute("SELECT item FROM items LIMIT %d,1000" % start_row) rows = cursor.fetchall() if not rows: break start_row += 1000 # Do something with rows... </code></pre> <p>However, this seems to get slower the higher start_row is.</p> <p>And no, using <code>fetchone()</code> instead of <code>fetchall()</code> doesn't change anything.</p> <h2>Clarification:</h2> <p>The naive code I use to reproduce this problem looks like this:</p> <pre><code>import MySQLdb conn = MySQLdb.connect(user="user", passwd="password", db="mydb") cur = conn.cursor() print "Executing query" cur.execute("SELECT * FROM bigtable"); print "Starting loop" row = cur.fetchone() while row is not None: print ", ".join([str(c) for c in row]) row = cur.fetchone() cur.close() conn.close() </code></pre> <p>On a ~700,000 rows table, this code runs quickly. But on a ~9,000,000 rows table it prints "Executing Query" and then hangs for a long long time. That is why it makes no difference if I use <code>fetchone()</code> or <code>fetchall()</code>.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USitsadok
    1. USitsadok
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    3. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow to get a row-by-row MySQL ResultSet in python
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POHow to get a row-by-row MySQL ResultSet in python
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POHow to get a row-by-row MySQL ResultSet in python
      1. This table or related slice is empty.
      1. VTUpMod
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload