Sql update statement for access database

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Data Structures. Operating System. Computer Network. Compiler Design. The brackets tell Access that all the words in the field name belong together. They also tell Access that "this is a field name" and so allows you to use otherwise reserved words for the names of fields such as [Date] which is also the name of a function without causing conflicts.

But I do this for another reason too. I know that if I see some text in square brackets I know it's a field name, whether it has spaces in it or not I like to write each clause of the SQL statement on a separate line.

This makes long statements much easier to read and edit Don't forget that each line must have both opening and closing quotes. The statement itself needs to be enclosed in quotes because it is a VBA text [gs string]. If you use the same type of quote mark for each Access will get confused. Look at this example Compare the two examples below. In the first example the VBA sees two text strings enclosed by double quote marks, and between them a word it doesn't know Paris so it generates an error.

But when the quote marks are alternated as shown in the second example, the problem doesn't arise. The VBA sees a text string enclosed by double quotes, inside which is some more text enclosed in single quotes. I working with multiple sets of quotes gets confusing, you can always use the ASCII character code for the double quote mark - Chr 34 - instead.

There is an example of this in the next section. Some of these rules are essential, others are just my way of doing things and that of many other database developers. Follow them and you will write good code that is easy to read and to debug.

The illustration below shows a completed SQL statement written the way I suggest [click the thumbnail to see a full-sized image] :. Working with Variables. But this won't often be the case. You might be changing the criteria, fields or even data sources specified in your SQL statements each time the code is run. The information that the SQL statement needs is often obtained from the user through their choices in a dialog box or from the values in fields on a [gs form].

Forthcoming tutorials in this series will show how this can be done. You want to allow the user to choose a value for the Office criteria each time the query is run, so you build a dialog box in which there is a combo box containing a list of Offices.

The combo box is named cboOffice. You can insert a reference to the value of the combo box directly into the SQL statement:. Alternatively, you can place the value of the combo box into a variable and then insert the variable into the SQL statement:. Using a [gs variable] can make the SQL statement code easier to read and understand, especially when there are several variable criteria to consider.

It is sometimes essential to use this method when the value has to be examined or manipulated in some way before it is passed to the SQL. Whatever method you choose, you must remember to include any necessary data type qualifiers in the SQL string. In the illustration below, a single quote mark is included in the SQL string either side of the text variable marked with red arrows :.

This method requires more typing but avoids conflicts and confusion arising from nesting quotes. Remember that as with " hard-coded " criteria, variables require the correct qualifiers for their data type: quotes for text, hash-marks pound signs for dates, and nothing for numbers. As with any other sort of programming, you SQL code can fail to work properly. It might be because you made a logic error , or got the SQL syntax wrong, or perhaps you just made a typo.

UPDATE is especially useful when you want to change many records or when the records that you want to change are in multiple tables. You can change several fields at the same time. The following example increases the Order Amount values by 10 percent and the Freight values by 3 percent for shippers in the United Kingdom:. This example changes values in the ReportsTo field to 5 for all employee records that currently have ReportsTo values of 2.

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