004 actionquery

Actions Queries Understanding Action Queries • Action queries are a way to make corrections to database They can make an enormous mess of database if used incorrectly • Action queries differ from select queries: – A select query shows you data that meet your criteria – An action query looks for the data that meets your criteria, and then does something with it, such as making changes to the data or moving records to a new table Testing Action Queries (Carefully) • Most importantly, before you use an action query, make a database backup! because it may not always generate the result you expect (mong đợi) • To make a backup, you can copy your accdb database file or File➝Save & Publish to enter Backstage view, look in the Advanced section of the Save Database As list Back Up Database The Action Query Family • An update query changes the values in one or more records • An append query selects one or more records, and then adds them to an existing table • A make-table query selects one or more records, and then creates a new table for them • A delete query deletes one or more records Update Queries • An update query searches for some records and then modifies them • Using the update query when you work on lots of data or when you want to update multiple fields • Update query makes to change multiple records at same time Update Queries • To Create a Update Query: – Select Create tab  Queries  Query Design – Add each table you want to include in query by selecting it and then clicking Add – Change query to an update query by choosing Query Tools  Design  Query Type  Update – Add the field you want to use for filtering, and then set the Criteria box for each one Update Queries – Add the field you want to change – In the Update To box, supply the new value that your query will apply to each field Update Queries – Add any other fields that you want to inspect to confirm that you’re selecting the correct records – Right-click the query’s tab title, and choose Datasheet View to see the rows that query affects – Now switch back to Design view, choose Query Tools  Design  Results Run to run update query and have Access apply your changes Update Queries • Access warns you about the change it’s about to make Click Yes to make the change • If you want to save your query, then press Ctrl+S You’ll need to supply a name for your query Append Queries • An append query selects records from a table and then inserts them into the end another table • You may want to use an append query to transfer records from one database to another This technique is handy if you have duplicate tables in different databases • To transfer the records, you need to make sure the two tables line up (Page 255) Append Queries • Create a new query by choosing Create Queries  Query Design • Using the Show Table dialog box, add the source table that has the records you want to copy • Query Tools Design ➝ Query Type ➝Append Append Queries – Another Database: transfer the records to another database click Browse to select database file OK – Table Name box: enter the name of the table to which you want to transfer the records – Click OK to close the Append or Make Table dialog box – Add the field you want to copy from the source table Append Queries – If you’re creating an append query, then fill in the names of the destination fields in the Append To boxes – If want to copy only some of the records in the source table, then set the filter conditions you need – Choose Datasheet View to see the rows that your query affects Append Queries – Switch back to Design view, and then choose Query Tools Design  Results  Run to transfer your records – Press Ctrl+S to save query Make-Table Query • The make-table query creates the destination table, and then copies the records to it – Open the source database – Choosing Create ➝ Queries ➝ Query Design – Add the source table that has the records you want to copy – Select Query Tools ➝ Design ➝ Query Type ➝ Make Table Make-Table Query – Another database: transfer the records to another Database, click Browse to select database file  OK – Table Name: enter the name of the table which you want to transfer the records Make-Table Query – Add the field you want to copy from the source table – To copy only some of the records in the source table, then set the filter conditions – Choose Datasheet View to see the rows that your query affects – Switch back to Design view  Results ➝ Run to transfer the records – Press Ctrl + S to save query Delete Queries • Delete queries are the simplest and most dangerous of the action queries • Delete query erases records from the database • To create a delete query: – Select Create tab ➝ Queries ➝ Query Design – Add the table that has the records you want to delete – Select Query Tools Design ➝ Query Type ➝ Delete Delete Queries – Add the fields you want to use for filtering, and then set filter conditions – Add the fields that you want to inspect to confirm you’re getting the correct records in the datasheet view – Choose Datasheet View to see the rows that’ll be affected by query – Switch back to Design view, choose Query Tools  Design  Results  Run to remove the records