Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>In a batch updates, the database works against a set of data, in a row by row update it has to run the same command as may times as there are rows. So if you insert a million rows in a batch, the command is sent and processed once and in a row-by row update, it is sent and processed a million times. This is also why you never want to use a cursor in SQL Server or a correlated subquery.</p> <p>an example of a set-based update in SQL server:</p> <pre><code>update mytable set myfield = 'test' where myfield is null </code></pre> <p>This would update all 1 million records that are null in one step. A cursor update (which is how you would update a million rows in a non-batch fashion) would iterate through each row one a time and update it.</p> <p>The problem with a batch insert is the size of the batch. If you try to update too many records at once, the database may lock the table for the duration of the process, locking all other users out. So you may need to do a loop that takes only part of the batch at a time (but pretty much any number greater than one row at time will be faster than one row at a time) This is slower than updating or inserting or deleting the whole batch, but faster than row-by row operations and may be needed in a production environment with many users and little available downtime when users are not trying to see and update other records in the same table. The size of the batch depends greatly on the database structure and exactly what is happening (tables with triggers and lots of constraints are slower as are tables with lots of fields and so require smaller batches).</p>
    singulars
    1. This table or related slice is empty.
    1. POWhy are batch inserts/updates faster? How do batch updates work?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USHLGEM
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    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. VTDownMod
    1. COThe idea that large updates will lock the users out is only true either with bad databases or with bad application developers. SQL Server has provided the standard 4 transaction isolation levels since V7.0, you have to do something outright wrong to block anything by inserting data.
      singulars
      1. PO
      1. USGreg Smith
 

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