Database Development

Trương Quý Quỳnh

References

• UDEMY: SQL Database MasterClass: Go From Pupil To Master!

• Database Systems - A Practical Approach to Design, Implementation, and Management by Thomas Connolly

Outline

• Sub-Queries• Joins• User-defined functions• Stored procedures• Views• SQL profiler, Optimizing

Sub-Queries

• A Subquery is a Select within a Select or a From or a Where.

• Example:Select Id,(Select Name from Person where

Id=Class.PersonID), PersonID from Class.Select ID, PersonID from (Select * from Class) C.Select ID,PersonID from Class where PersonID in

(Select ID from Person where Name=“QuynhTQ”)

Sub-Queries

• Advantages– To quickly get more data from another Table.– To Optimize a SQL Statement.

• Disadvantages– Performance issues.

Joins

• Inner join– When use inner join, you are telling the DB that I

have 2 tables and those tables have relationship where value1=value2.

– When use inner join, I will not show value from either table or row where this statement is not true.

• Outer join– Usually used “left outer join”.

User-defined functions

• Scalar function– Returns only 1 value.–Can not join to scalar function– If you put it in select, it will execute 1 time for

every row.• Table function– Returns a table variable– Can join to table function

Stored procedures

• Store procedure is similar to UDFs but returns zero or more values.

Views

• A view is a way to save a query for later use.• A table holds all its data, but view is a smaller

portion. Like a window looking to the house at the table.

View

• Advantages.– Save queries.– Security.

• Disadvantages.– Performance.

Introduction to SQL profiler

Optimize SQL

• Remove Scalar UDFs (Replace with view wherever possible)

• Join properly• Move where to join clause if possible• Query object order• Add indexes• Remove cursors