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What is the sub query in the FROM clause of an SQL statement?
From clause can be used to specify a sub-query expression in SQL. The relation produced by the sub-query is then used as a new relation on which the outer query is applied. Sub queries in the from clause are supported by most of the SQL implementations.
Is a query that has another query embedded within it?
A Subquery or Inner query or a Nested query is a query within another SQL query and embedded within the WHERE clause. A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved.
How are sub queries used in the FROM clause?
The relation produced by the sub-query is then used as a new relation on which the outer query is applied. Sub queries in the from clause are supported by most of the SQL implementations. The correlation variables from the relations in from clause cannot be used in the sub-queries in the from clause.
Can a subquery be moved into a from clause?
I voted up on all answers that contributed to this new query. The subquery in the IN clause does not depend on anything in the outer query. You can safely move it into FROM clause; a sane query plan builder would do it automatically. Also, calling EXPLAIN PLAN on any query you’re going to use in production is a must.
When to use a subquery in an expression?
You can write a subquery in an expression or in a Structured Query Language (SQL) statement in SQL view. You can use a subquery as a field alias. Use a subquery as a field alias when you want to use the subquery results as a field in your main query.
How to nest a query in a subquery?
For each row, the subquery selects the most recent order date that is less recent than the order date that is already associated with the row. Note how you use the AS keyword to create a table alias, so that you can compare values in the subquery to values in the current row of the main query.