SQL statements Add fields, modify fields, modify types, modify default values

--First, modify the field default valueAlter TableTable nameDrop constraintConstraint name------Description: Delete the original constraint for a table fieldAlter TableTable nameAdd constraintConstraint nameDEFAULTDefault value forField name-------Description: Add a constraint for a table's field and specify a default value--Second, modify the field name:Alter TableTable name RenamecolumnA toB--Third, modify the field type:Alter TableTable nameAlter columnUnitPricedecimal( -,4) not NULL --Iv. Modify the Add field:Alter TableTable nameADDField type not NULL Default 0

SQL statements Add fields, modify fields, modify types, modify default values