0 Interview questions

How to find the date diffrence greater than a particular number using mysql?
 eg: date difference is greater than 10
Ans:DATEDIFF( );
       eg:SELECT DATE_FORMAT(FROM_DAYS(DATEDIFF(NOW(), dob)),
"%Y")+0 AS age from     sometable

Q.Find the records match in table,and also stop when first match occurs?

Ans:SELECT * FROM (     SELECT * FROM table WHERE name1 like "Bob" limit 1     UNION SELECT * FROM table WHERE name2 like "Bob" limit 1     UNION SELECT * from table WHERE nicknames rlike  "[,]Bob[,]|[,]Bob$" limit 1) AS t1 LIMIT 1; The limit 1 on each one keeps the database from pulling up 50,000 Bob records just to show you one of them. Q .how to optimize sql querys? Ans:     * Use primary keys     * Avoid select *     * Be as specific as you can when building your conditional statements     * De-normalisation can often be more efficient     * Table variables and temporary tables (where available) will often be  better than using a large source    table     * Partitioned views     * use indices and constraints Q.Difference b/w having and where?     If a condition refers to an aggregate function, put that condition in the HAVING clause.  Otherwise, use the    WHERE clause. Here's another rule: You can't use HAVING unless you also use GROUP BY. SELECT state,SUM(baldue) FROM Test GROUP by state HAVING SUM(baldue) > 0 ORDER BY state