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Difference between union and union all in oracle sql plsql

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"This is one of the most important questions that interviewer might be asking in an interview.Infyosis,Linked group,Kyndryl,Vodafone Idea, IBM and Mphasis etc." INTRODUCTION: It is said to be set operators which is used to combine, add or concatenate two or more result sets. It is used in the multiple select statements where to combine to produce the final desired results. In other words, multiple select statements of similar column name in same order and having same data type to produce the unified result. It merges the content of the two structurally compatible organized tables into single table.  In MIS datalake,when you are adding the modules of GST reconciliation which is to be used in micros in Excel or VB script, union and union all set operator is preferred for eliminating duplicate records or keeping duplicate records as per business requirement. There are several alternatives like bulk collect,join,set operators like intersect & minus for combining the data from...
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Difference between full join and cross join-oracle sql plsql

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 Difference between full join and cross join in sql:- They behave differently to combine the rows from the two tables. FULL OUTER JOIN: It is also called as the full join .It will return all the rows when there is either match in the left table or right table. If there is no match, it will return NULL for the rows of the columns which is lacking the matching rows. Syntax: select c.*,d.*  from tableC c FULL OUTER JOIN tableD d on c.id=d.id; select e.ename,d.dname from emp e FULL OUTER JOIN dept d ON e.deptno=d.deptno; When you want to retain the unmatched rows i.e operations which is not present in the emp table and having deptno as 40.So,ename is appeared as NULL. CROSS JOIN: It returns the cartesian product of both the tables i.e. Every row of the table A is combined with every row of the table B.ON condition is not used due to not match rows. Syntax: select c.*.d.* from tableC c CROSS JOIN tableD d; select e.ename,d.dname from emp e CROSS JOIN dept d; ENAME ...
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What is hash join in oracle with example?SQL PLSQL

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  INTRODUCTION: It is the join strategy where the one table data is loaded into the hash table for an efficient lookup. Other table data is scanned to match with the hash table which is suitable for the large datasets. Database optimizer uses the two of the smaller tables to build the hash table into the memory. Its function is used to map join key values to the hash table locations. Larger table is also scanned for each row. It's fast and efficient for quick matching of rows which is based on the join condition. It is an effective when one or both of the tables are large and cannot fit in the memory. It is also effective when the join condition is an equally predicate i.e. table1.column=table2.column. It's cost is limited to the single read pass which is over the two data sets. It is situated in the PGA and the rows are accessed without latching. It will reduce I/O by preventing the necessity of repeatedly latching and reading blocks in the database buffer cache. If the data s...
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