Contents
Which class is used to execute the queries?
To execute SQL expressions, use the following query object classes: ValueReadQuery : Returns a single data value. DirectReadQuery : Returns a collection of column values; can be used for direct collection queries. DataReadQuery : Executes a SQL SELECT, returns a collection of database row (map) objects.
What is a DB class?
A database class is any class that extends the virtual class database . Once the required methods for dbread , etc. are defined or inherited, you can attach an object of the class and use the resulting database like any other.
What is SQL clause?
Clauses are in-built functions available to us in SQL. With the help of clauses, we can deal with data easily stored in the table. When we have large amounts of data stored in the database, we use Clauses to query and get data required by the user. Some of the examples of clauses are – where, and, or, like, top, etc.
What type of Statement can execute parameterized queries?
PreparedStatement: It represents the pre-compiled SQL statements that can be executed multiple times. CallableStatement: It is used to execute SQL stored procedures.
Which is the subquery of the main query?
A subquery is a query within another query. The outer query is called as main query and inner query is called as subquery. The subquery generally executes first, and its output is used to complete the query condition for the main or outer query. Subquery must be enclosed in parentheses. Subqueries are on the right side of the comparison operator.
How to nest a query inside another query?
Click Northwind, and then click Create. Follow the directions on the Northwind Traders page (on the Startup Screen object tab) to open the database, and then close the Login Dialog window. On the Create tab, in the Queries group, click Query Design. Click the Queries tab, and then double-click Product Orders.
When to use a query as a field?
Sometimes you may want to use the results of a query as a field in another query, or as a criterion for a query field. For example, suppose that you want to see the interval between orders for each of your products. To create a query that shows this interval, you need to compare each order date to other order dates for that product.
When to use a where clause in a query?
IN Use IN in a WHERE clause to verify that a value in the current row of the main query is part of the set that the subquery returns. You can also preface IN with NOT, to verify that a value in the current row of the main query is not part of the set that the subquery returns.