Select queries.
These are the queries that extract or show us data. They will show data that complies with specific criteria.
Once we have the result we can consult the data and edit it (this can or cannot be done, depending on the query). A select query generates a logical table (named this way because it is not actually in the hard drive but in the memory of the computer, and every time we open it is recalculated).
This is the most common type of query.
Action queries.
These are the queries that carry out changes to the records. Various types of action queries exist to delete, update, insert data, and to create a new table from one existing table. These queries are named delete queries, update queries, append queries and Make-Table queries.
Crosstab queries.
We use these queries to calculate and restructure data for easier analysis. Crosstab queries calculate a count, average, sum, or other type of total for data that is grouped by two types of information (two fields), one down the left side of the datasheet and another across the top.
SQL queries.
When we want some action to be made on the data, we must tell Microsoft Jet engine to do it. SQL is the language that Microsoft jet engine understands and permits us to comunicate to it.
When you create a query in Query Design View, Access constructs the equivalent SQL statement behind the scenes for you. If you want, you can view and edit the SQL statement in SQL view.
After you make changes to the query in SQL view, the Query Design view will change and adapt to the new SQL sentence. However, sometimes, query might not be displayed in Query Design view because of the SQL sentence.
There is some statements that can not be defined from the Query Design View but rather directly in SQL, these are SQL-specific queries.
These queries will not be studies in this course as in order to define them knowledge of SQL is necessary, which is not part of the objective of this course. |