Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <blockquote> <p><strong>Editor warning: This solution is computationally inefficient and may bring down your connection for a large table.</strong></p> </blockquote> <p><strong>NB - You <em>need</em> to do this first on a <em>test copy</em> of your table!</strong></p> <p><strong>When I did it, I found that unless I also included <code>AND n1.id &lt;&gt; n2.id</code>, it deleted every row in the table.</strong></p> <ol> <li><p>If you want to keep the row with the lowest <code>id</code> value: </p> <pre class="lang-sql prettyprint-override"><code>DELETE n1 FROM names n1, names n2 WHERE n1.id &gt; n2.id AND n1.name = n2.name </code></pre></li> <li><p>If you want to keep the row with the highest <code>id</code> value:</p> <pre class="lang-sql prettyprint-override"><code>DELETE n1 FROM names n1, names n2 WHERE n1.id &lt; n2.id AND n1.name = n2.name </code></pre></li> </ol> <p>I used this method in MySQL 5.1</p> <p>Not sure about other versions. </p> <hr> <p><strong>Update: Since people Googling for removing duplicates end up here</strong><br> Although the OP's question is about <code>DELETE</code>, please be advised that using <code>INSERT</code> and <code>DISTINCT</code> is much faster. For a database with 8 million rows, the below query took 13 minutes, while using <code>DELETE</code>, it took more than 2 hours and yet didn't complete. </p> <pre><code>INSERT INTO tempTableName(cellId,attributeId,entityRowId,value) SELECT DISTINCT cellId,attributeId,entityRowId,value FROM tableName; </code></pre>
    singulars
    1. This table or related slice is empty.
    1. PODelete all Duplicate Rows except for One in MySQL?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USivan_pozdeev
    1. USmartin.masa
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PODelete all Duplicate Rows except for One in MySQL?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COExcellent solution. It worked perfectly. But I have one suggestion here we should swap the conditions. Instead of [WHERE n1.id > n2.id AND n1.name = n2.name] we should write [WHERE n1.name = n2.name AND n1.id > n2.id] it will improve performance if we have so much data.
      singulars
      1. PO
      1. USuser307635
    2. COFYI: This ignores rows where column "name" is null.
      singulars
      1. PO
      1. USa coder
    3. COhttp://sqlfiddle.com/#!2/e5df9 for a schema example. May need to load in your instance of MySQL. Then execute: SELECT * FROM deldup; DELETE n1 FROM deldup n1, deldup n2 WHERE n1.or_id < n2.or_id AND n1.order_id = n2.order_id AND n1.txt_value = n2.txt_value AND n1.date_of_revision = n2.date_of_revision AND n1.status = n2.status; SELECT * FROM deldup;
      singulars
      1. PO
      1. USa coder
 

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