FREE URDU/HINDI Lecture 29 Self Join in Oracle PL/SQL
SQL stands for Structured Query Language. SQL is a scripting language expected to store, control, and inquiry information put away in social databases. The main manifestation of SQL showed up in 1974, when a gathering in IBM built up the principal model of a social database. The primary business social database was discharged by Relational Software later turning out to be Oracle.
Models for SQL exist. In any case, the SQL that can be utilized on every last one of the major RDBMS today is in various flavors. This is because of two reasons:
1. The SQL order standard is genuinely intricate, and it isn’t handy to actualize the whole standard.
2. Every database seller needs an approach to separate its item from others.
Right now, contrasts are noted where fitting.
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SQL Self Join is the kind of join in which a table is joined with itself means we are joining a table with that same table (which is also called Unary relationships), especially when the table has the FOREIGN KEY which references its PRIMARY KEY. If we want to join the table itself means that each row of the table is combined with itself and with every other row of the table.
The self join allows you to join the table to itself. It is useful for querying the hierarchical data or comparing rows within the same table. Till now, we have seen the Outer Join, Cross Join, Left Join, SQL Joins Overview and Inner Join in this blog.
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CROSS JOIN is in the spotlight. This article finishes our small series of SQL JOIN-related publications.
SQL Server CROSS JOIN is the simplest of all joins. It implements a combination of 2 tables without a join condition. If you have 5 rows in one table and 3 rows in another, you get 15 combinations. Another definition is a Cartesian Product.
Now, why would you want to combine tables without a join condition? Hang on a bit because we are getting there. First, let’s refer to the syntax.
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Inner join, outer join, cross join? What gives?
It’s a valid question. I once saw a Visual Basic code with T-SQL codes embedded in it. The VB code retrieves table records with multiple SELECT statements, one SELECT * per table. Then, it combines multiple result sets into a record set. Absurd?
To the young developers who did it, it was not. But when they asked me to evaluate why the system was slow, that issue was the first to catch my attention. That’s right. They never heard of SQL joins. In fairness to them, they were honest and open to suggestions.
How do you describe SQL joins? Perhaps, you remember one song – Imagine by John Lennon:
You may say I’m a dreamer, but I’m not the only one.
I hope someday you’ll join us, and the world will be as one.
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Outer join is at the center stage today. And this is part 2 of your ultimate guide to SQL joins. If you missed part 1, here’s the link.
By the looks of it, outer is the opposite of inner. However, if you consider the outer join this way, you’ll be confused. To top that, you don’t have to include the word outer in your syntax explicitly. It’s optional!
But before we dive in, let’s discuss nulls concerning outer joins.
When you join 2 tables, one of the values from either table can be null. For INNER JOINs, records with nulls won’t match, and they will be discarded and won’t appear in the result set. If you want to get the records that don’t match, your only option is OUTER JOIN.
Going back to antonyms, isn’t that the opposite of INNER JOINs? Not entirely, as you will see in the next section.
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