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10 Newer Entries Showing entries 61 to 70 of 1033 10 Older Entries

Displaying posts with tag: sql (reset)

EXPLAIN UPDATE in MySQL 5.6
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I just tried out EXPLAIN UPDATE in MySQL 5.6 and found unexpected results. This query has no usable index:


EXPLAIN UPDATE ... WHERE col1 = 9 AND col2 = 'something'\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: foo
         type: index
possible_keys: NULL
          key: PRIMARY
      key_len: 55
          ref: NULL
         rows: 51
        Extra: Using where

The EXPLAIN output makes it seem like a perfectly fine query, but it’s a full table scan. If I do the old trick of rewriting it to a …

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MySQL Synonym?
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Somebody asked how to create a SYNONYM in MySQL, which is interesting because MySQL doesn’t support synonyms. I thought the prior entry explained how to do it, but here’s a new post. However, you can create a view in one database that relies on a table in another database.

The following SQL statements create two databases and grant appropriate privileges to the student as the root superuser:

/* Create two databases. */
CREATE DATABASE seussdb;
CREATE DATABASE appdb;
 
/* Grant …
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MariaDB: DELETE … RETURNING
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MariaDB 10.0.5 supports DELETE ... RETURNING, like PostgreSQL. It deletes some rows and returns the specified columns (or, more generally, the specified SELECT expressions) from the deleted rows. As for regular DELETEs, Com_delete is incremented and Com_select is not.

Let’s see what this feature does and what it does not.

You cannot:

  • Cannot use it with INSERT or CREATE TABLE to create a …
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Introducing MySQL Connector/Arduino 1.0.0 beta
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There is a new release of the Connector/Arduino on Launchpad! See https://launchpad.net/mysql-arduino. The new version supports a number of refinements and a few new features. These include:

  • Improved support for processing result sets
  • Conditional compilation to omit result set handling features to save program space
  • Support for the Arduino WiFi shield
  • New version() method to check version of the connector
  • Simplified download (no more patching SHA1!)


So What is It?
If you have never heard of Connector/Arduino, it is simply a library designed …


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Announcing: New Forum for Connector/Arduino!
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Due to the growing popularity of Connector/Arduino, the moderator of MySQL Forums has created a forum for us to meet up and discuss the connector. Yippie!

http://forums.mysql.com/list.php?175

While the forum has been started very recently, I expect it will grow quickly as people discover the connector for the first time and experienced users find new and interesting ways to use it. I hope to moderate the new forum periodically to answer questions and respond to posts. See you there!

Note: you need an account to write to the forum. Click on …





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Building Queries Systematically
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The SQL language is a bit like a toolkit for data. It consists of lots of little fiddly bits of syntax that, taken together, allow you to build complex edifices and return powerful results. For the uninitiated, the many tools can be quite confusing, and it's sometimes difficult to decide how to go about the process of building non-trivial queries, that is, queries that are more than a simple SELECT a, b FROM c;

A System for Building Queries

When you're building queries, you could use a system like the following: 

  1. Decide which fields contain the values you want to use in our output, and how you wish to alias those fields
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MySQL isn’t limited to nested-loop joins
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I have followed the “Use the Index, Luke!” blog for a while. Today Marcus wrote that (I’ll paraphrase) MongoDB disgraces NoSQL the same way that MySQL disgraces SQL. I agree with a lot of this, actually, although I’m not sure I’d put it so strongly. People often like products for good reasons, and to think that legions of developers are stupid or ill-educated is suspect, in my opinion.

But that wasn’t what I meant to write about. I …

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It happened again
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Oracle released a bunch of MySQL stuff they’ve been working on since the last huge release, and my blog reader filled up with a few dozen posts I’m gonna have to read through …

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How to find unused MariaDB/MySQL accounts
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In MariaDB and Oracle MySQL, an account is a user_name@host combination, where host can be an ip address (v4 or v6) or a hostname. Also, the host part can be specified as a LIKE pattern (such as '161.58.%'). The account used by the connection determines the privileges for that connection. When a connection matches more than one account, only one is used, and privileges assigned to other accounts will be ignored.

It can happen that you think that a certain client uses an account, but it uses a different account. For this reason, in this post I’ll show the queries to get all defined accounts, plus the accounts that were …

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Sending the query to the data
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It’s common wisdom that large-scale database systems require distributing the data across machines. But what seems to be missing in a lot of discussions is distributing the query processing too. By this I mean the actual computation that’s performed on the data.

I just had a conversation with Peter Zaitsev yesterday that helped make concrete some thoughts I’ve been having about Cassandra for a while. Because Cassandra doesn’t allow you to really do any computation in the data (aggregating, evaluating expressions, and so on), if you’re going to use it for truly Big …

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10 Newer Entries Showing entries 61 to 70 of 1033 10 Older Entries

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