These data rules are coded to aid the end user with the required data joins but also to ensure that the data on these key values (the DEPTNO in this example code) always has a match. This is called Referential Integrity, Parent/Child Relationships, or Primary/Foreign Key Relationships. Most applications have the table relationships coded into the table data stores themselves. ANSI SQL is the common SQL across the relational database industry.
ANSI SQL is commonly used and is a requirement for using any ODBC driver access. This is the ANSI (American National Standards Institute) SQL. This illustration shows the SQL joining the EMP and the DEPT tables together using the DEPTNO column. In this example, the Join condition on the DEPTNO columns is automatically painted in with an equality type of join (equal condition…called an Equi-Join). This example is showing Query Builder and an Oracle RDBMS where there are pre-programmed relationships between the various tables. SQL table joins allow for these descriptions to easily be pulled into the result set when needed. SQL Table Joins - EMP and DEP Join Condition This cuts way down on data redundancy and needlessly storing lengthy descriptions with the rows of data. in a separate table, and keep just the code for the description with the data.
One of the things you can do in the relational world is keep full descriptions of codes, part numbers, inventory items, etc. In my experience, I see up to a dozen tables being joined together via SQL table joins for various reasons. These data stores will have to have a column of common data, the join condition, for each pair of tables involved. SQL table joins are needed when you want to access data from two or more different data stores in the relational model. In this blog, the TDP Helpful Techniques will be creating the same SQL using Query Builder. You can always make all the changes using just QB though. Often, I will use QB to create the base SQL, then I will tweak the SQL it created. This feature also has a 'query' tab that allows for the SQL to be reviewed and tweaked. Query Builder allows queries to simply be built, just using a mouse. I will also illustrate doing similar items using Query Builder (QB). This blog will focus on these areas of the SQL query language using Traditional Toad Data Point: The tables are listed in the FROM clause of the SQL, and the WHERE clause is used to match up the columns from two of these tables (at a time) to have data coordinated based on the contents of a column of data. SQL allows for quite a number of data stores to be merged into a single SQL statement. They are a way of eliminating data redundancy and allowing the user of the data to select what they want from the data stores necessary. SQL table joins are common practice in the relational database world.