Posts

Display row number in Mysql Select Query

How many times did want to have the row number or the position of the row in the selected query? I had many cases where I needed this feature. I needed the feature for printing the rank of a person where each row is the mark of the person. So lets see how  …

Important MySQL DBA Interview Questions

Here are a few sets of interview questions expected for MySQL DBA position.These are compilation of the usual questions from various DBA texts: What is Log Switch? – The point at which ORACLE ends writing to one online redo log file and begins writing to …

Get the nth Word from a text field in mysql

I had a requirement to get the nth word out of a string and sort or order by the same. This is used when the text is stored in a purticular format and you would want to order it according to that or group it or so on. So how is it done? We do it using a  …

Check if a table exists in MySQL from PHP

Sometimes its necessary to execute a query or execute some code if a table exists or not. So a bit of searching got me to the conclusion that mysql doesn’t have a direct query or method for it from php. So there are two methods to do it. Use the mysql c …

Group by Date when Stored in Mysql DataBase as Date Time

I have a table called date_count with 2 columns one is a value and another is a date time, say called date_time in mysql. Date Time in mysql is stored as dd-mm-yy hh:mm:ss. The issue comes when I need to get the number of rows per day. As its stored as dat …

Generate Date from a range in Mysql and pad the results where no date is present

If you want to generate dates, MYSQL doesn’t have a range function, so I wrote a work around for the same. So how  it works is I have reused a code to generate numbers from my previous post. So I added date function to that query and reduce the generated  …

Batch Insert/Update for Mysql in Java

Large inserts/Updates are a costly operation. One foolish way that I used to do is to run each update or insert query one at a time. Its incredibly slow. With most of the systems currently the latency is what is killing the performance not the CPU. Hence l …

Find Invisible Users In Gmail

Finding who is invisible is something that I always wanted to do.It’s always fun to ping a person who feels none can see him/her online. While studying XMPP protocol I found out that even when the person is offline the chat client knows that person is onli …

Generate 1 to 1000 in mysql

Sometimes its necessary to have thousand rows to join or generate new values, we need to get the thousand rows first. For this I used union of numbers 0-9.  I have joined four of these to get to four digit values. So here is the code:



SELECT @row := …

Customizing Mysql Prompt For multiple Servers

If you are using mysql regularly on multiple servers its really useful to have the promt in mysql to show something more than mysql>. It would be useful if it showed the username,hostname, current database and things like that. So how to do this. One m …