- What is equi join?
- Is inner join and equi join same?
- Why is self Join needed?
- What is the difference between where and having clause in SQL?
- Which SQL statement is used to return only unique values?
- What is self join with example?
- How can we avoid Cartesian join?
- What is a non equi join?
- What are the after triggers?
- Which SQL keyword is used to retrieve a maximum value?
- Which are the join types in join condition?
- Which operation is allowed in a join view?
- How many join conditions are needed in JOIN query to avoid a Cartesian product?
- What is join condition?
- What is used to retrieve records that do not meet the join condition?
- What is the difference between a left join and a right join?
- Which join is faster in Oracle?
- Why do we use joins?
What is equi join?
An equi join is a type of join that combines tables based on matching values in specified columns.
The column names do not need to be the same.
The resultant table contains repeated columns.
It is possible to perform an equi join on more than two tables..
Is inner join and equi join same?
An equijoin is a join with a join condition containing an equality operator. An equijoin returns only the rows that have equivalent values for the specified columns. An inner join is a join of two or more tables that returns only those rows (compared using a comparison operator) that satisfy the join condition.
Why is self Join needed?
It is useful for querying hierarchical data or comparing rows within the same table. A self join uses the inner join or left join clause. Because the query that uses self join references the same table, the table alias is used to assign different names to the same table within the query.
What is the difference between where and having clause in SQL?
WHERE Clause is used to filter the records from the table based on the specified condition. … HAVING Clause is used to filter record from the groups based on the specified condition.
Which SQL statement is used to return only unique values?
SQL SELECT DISTINCT StatementThe SQL SELECT DISTINCT Statement The SELECT DISTINCT statement is used to return only distinct (different) values.
What is self join with example?
A self JOIN occurs when a table takes a ‘selfie’, that is, it JOINs with itself. A self JOIN is a regular join but the table that it joins to is itself. This can be useful when modeling hierarchies. SELF JOINs are also useful for comparisons within a table.
How can we avoid Cartesian join?
To avoid Cartesian products, every view in the from clause must be connected to each of the other views by a single join predicate, or a chain of join predicates. These are some cases when Cartesian products between two views do not introduce a performance bottleneck.
What is a non equi join?
Non-equi joins are joins whose join conditions use conditional operators other than equals. An example would be where we are matching first name and then last name, but we are checking where one field from a table does not equal field from another table.
What are the after triggers?
After Trigger in SQL Server These kinds of triggers fire after the execution of an action query that can be either DDL statements like Create, Alter and Drop or DML statements like Insert, Update and Delete.
Which SQL keyword is used to retrieve a maximum value?
MAXMAX() is the SQL keyword is used to retrieve the maximum value in the selected column.
Which are the join types in join condition?
Explanation: There are totally four join types in SQL. Explanation: Types are inner join, left outer join, right outer join, full join, cross join. Explanation: RIGHT OUTER JOIN: Return all rows from the right table and the matched rows from the left table.
Which operation is allowed in a join view?
GROUP BY or HAVING clauses. Set operations, such as UNION, UNION ALL, INTERSECT, MINUS. Aggregate functions, such as AVG, COUNT, MAX, MIN, SUM, and so forth. The DISTINCT operator.
How many join conditions are needed in JOIN query to avoid a Cartesian product?
1 join conditionsIn general, if you join n tables, you need n – 1 join conditions to avoid a Cartesian product. Of course, using more than n – 1 join conditions, as well as other conditions, is certainly permissible to further reduce the result set.
What is join condition?
A join condition involves columns that relate two tables in some logical way. A join condition may involve more than one column. This is usually the case when a foreign key constraint consists of multiple columns. The total number of join conditions in a query is always equal to the total number of tables less one.
What is used to retrieve records that do not meet the join condition?
Answer. SQL view is used to retrieve records that do not meet the join condition. View command is used for security purposes as it displays only selected commands. … It enhances the security mechanism of a database.
What is the difference between a left join and a right join?
The key difference between a left outer join, and a right outer join is that in a left outer join it’s the table in the FROM clause whose all rows are returned. Whereas, in a right outer join we are returning all rows from the table specified in the join clause.
Which join is faster in Oracle?
– hash join with parallel hints: Fastest when joining a large table to a small table, hash joins perform full-table-scans, which can be parallelized for faster performance.
Why do we use joins?
The SQL Joins clause is used to combine records from two or more tables in a database. A JOIN is a means for combining fields from two tables by using values common to each. Now, let us join these two tables in our SELECT statement as shown below.