Change Table tb Change Column aa Bytes [Bytes]

Alter table TB alter column aa long number [long integer]

ALTER TABLE tb ALTER COLUMN aa short number [integer]

Change Table TB Change Column aa Single Number [Single Precision]

Alter table TB alter column aa double number [double precision]

Change table TB change column aa currency

Change table tb change column aa character text

Alter table TB alter column aa text (n) text, where n represents the field size.

Change table TB change column aa binary

Change table TB change column aa counter automatic numbering

Change table tb change column aa memo remarks

Change Table tb Change Column aa Time Date/Time

In the Design view of a table, each field has a design type, and Access allows nine data types: text, memo, numeric value, date/time, currency, autonumber, yes/no, OLE object, hyperlink and query wizard.

Text: This type allows up to 255 characters or numbers. The default size of Access is 50 characters, and the system only saves the characters entered into the field, and does not save the empty characters in the unused positions in the text field. You can set the field size property to control the maximum character length that can be entered.

Note: This type is used to store long text and numbers, and it allows fields to store up to 64,000 characters. However, Access cannot sort or index memo fields, but it can sort and index text fields. Although you can search for text in a memo field, it is not as fast as searching in an indexed text field.

Number: This field type can be used to store numerical data of arithmetic calculation. Users can also set the field size property to define a specific number type. Any font designated as a numeric data type can be set to five types: byte, integer, long integer, single precision, double precision, synchronous copy ID and decimal. In Access, it usually defaults to "double precision number".

Date/Time: this type is used to store date, time or date and time together. Each date/time field needs 8 bytes to store space.

Currency: This type is a special type of numeric data type, which is equivalent to a double-precision numeric field type. When you enter data in the currency field, you don't need to type RMB symbols and thousands of commas. Access will automatically display the RMB symbol and comma, and add two decimal places in the currency field. When the decimal part exceeds two digits, Access will round the data. The accuracy is 15 digits to the left and 4 digits to the right of the decimal point.

Automatic numbering: This type is special. Every time you add a new record to the table, Access automatically inserts a unique sequence or random number, that is, specifies a value in the AutoNumber field. Once an automatic number is assigned, it will be permanently associated with the record. If you delete a record that contains an autonumber field in a table, Access will not renumber the autonumber field in the table. When adding a record, Access no longer uses the value of the deleted AutoNumber field, but redistributes it according to the increasing law.

Yes/No: Set this field for a field that contains only two different optional values. The user can select the Yes/No field through the format characteristics of the Yes/No data type.

OLE object: This field indicates that the field allows OLE objects to be "linked" or "embedded" individually. When adding data to an OLE object field, OLE objects that can be linked or embedded in an Access table refer to objects created in other OLE protocol programs, such as WORD documents, EXCEL spreadsheets, images, sounds or other binary data. The maximum size of OLE object field is 1GB, which is mainly limited by disk space.

Hyperlink: This field is mainly used to store hyperlinks, including text as hyperlink address or a combination of characters and numbers stored as text. When you click the hyperlink, the WEB browser or Access will reach the specified target according to the hyperlink address. A hyperlink can contain at most three parts: one is the text displayed in a field or control; The second is the path of the file or page; The third is the address in the file or page. The easiest way to insert a hyperlink address in this field or control is to click Hyperlink on the Insert menu.

Find Wizard: This field type provides users with a list of field contents, which can be selected as the content added to the field.

Yes, add true/false or 0/ 1.