I have given three ideas to improve SQL performance in this post. Quickly you can implement in your project.
Derived Table in DB2 is a solution to avoid complex SQL query. After deriving you use that table whenever you need in that main SQL query.
SQL DATE and Time comparison popular styles and SQL queries useful to read for your project.
Load utility in DB2, to load bulk data, very popular. The questions given in this post are useful for interviews.
Locks and Concurrency are tricky words. Understand the real purpose of these mechanisms for better use of database.
SYSIBM catalog tables are base tables defined under this schema. There are many schemas defined in DB2. To your quick reading, I have given all the key points here.
Data access is much faster in Hashing compared to the index. Read the differences between Hashing and Index.
Having Vs Where clause in SQL real usage is to filter rows on aggregate totals. Read more.