Latest articles under General SQL category

Swap values in 2 rows SQL

I encountered a situation at work that I feel would be a good brain teaser. I was working on a project and needed a way to swap values from 2 different rows in a SQL table. Obviously I can do it on client side (like PHP) to do it; but that wouldn’t be a good […]

Posted on October 11th, 2009 under General SQL, MySQL, PostgreSQL  •  16 Comments

Use EXISTS() instead of COUNT(*)

A lot of times, I saw programmers use COUNT(*) and check if the result is greater than 0 to see if a particular record exits in a table. If your only purpose is to know if a record exists or not and you don’t really care about how many matched records are there, the better […]

Posted on June 30th, 2009 under General SQL  •  3 Comments

Comparing data from 2 database tables

During development cycle, I often come to a case where I need to compare two tables whether they are the same or not. For example, if you already have a running script that outputs to a database table in production that was written sub-optimally and you need to improve it. You want to make sure […]

Posted on March 1st, 2009 under General SQL, MySQL, PostgreSQL  •  6 Comments

Adding script name on SQL queries

Have you ever done SHOW FULL PROCESSLIST on MySQL and found that there are some queries that has been running for a long time? Then you tried to find out from where the query was initiated so that you can debug those script only to find out that there are many similar queries from different […]

Posted on February 10th, 2009 under General SQL, PHP  •  1 Comment

Keep replication in mind when writing SQL code.

This is something I got "bitten" once, especially if you have a development server with its own database not replicated and production database is replicated. That slight difference is enough to cause production problems that may not be noticeable days after production release. As a wise man say: When programming SQL statements, be mindful of […]

Posted on February 8th, 2009 under General SQL, Quick Tips  •  No Comments

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