What is the difference between a column constraint and a table constraint?
Constraints can be specified for individual columns as part of the column specification (column-level constraints) or for groups of columns as part of the table definition (table-level constraints). Show
The constraint has the following syntax: [CONSTRAINT constraint_name] constraint Defines a name for the constraint. If the name is omitted, the DBMS Server assigns one. The constraint name is used when dropping the constraint using the ALTER TABLE statement. Note: We recommend defining a name when creating a constraint; otherwise system catalogs must be queried to determine the system-defined name. Is either a column-level constraint (column_constraint) or table-level constraint (table_constraint). Table constraints are validations which can be applied on a group of columns of the table. For exp – CHECK, UNIQUE etc. Column level constraints are validations which can be applied on individual columns of the tables. For exp – NOT NULL, DEFAULT etc. Table ConstraintsColumn ConstraintsIt appears at the end of table definitionIt appears with the column of table definitionNOT NULL is not allowedNOT NULL is allowedMy select statement is not working as expected, So, to overcome from such issues what are the steps needed to be taken care? 2 Answers CG, Hi Guys, I have a situation where I need to access the column values from rowtype variable. However, the column names are dynamic. below is sample code: declare Cursor c1 is select * from emp; Cursor c2 is select column_name from xyztable; v_c2 c2%rowtype; v_str varchar2 v_value varchar2(200); begin for rec in c1 loop open c2;---this cursor has column names like EMPLOYEE_ID, FIRST_NAME, LAST_NAME etc. loop fetch c2 into v_c2; exit when c2%notfound; /* now lets say i want to access value of LAST_NAME from cursor c1, so I am writing below code, however it does not work as expected */ v_str:= 'rec.'|| v_c2.column_name; -- this will give me string like "rec.EMPLOYEE_ID" v_value:=v_str; end loop; end loop; end; / Plz help ASAP.Thanks. 2 Answers What action do you have to perform before retrieving data from the next result set of a stored procedure ? are user defined requirements that define what values are valid for a column or table. You can think of them as additional restrictions to narrow in on acceptable values more strictly than data types allow. Constraints allow you to define qualities that all entries must have, with the server itself enforcing the restrictions upon data entry or update. As an example, it might not make sense for a column representing boiling point of various substances to be lower than its freezing point. A constraint can enforce this type of requirement, even though types would not be able to. Where constraints are defined: column vs table constraintsMySQL allows you to create constraints associated with a specific column or with a table in general. Almost all constraints can be used in both forms without modification: ConstraintColumnTableCHECKYesYesNOT NULLYesNo*UNIQUEYesYesPRIMARY KEYYesYesFOREIGN KEYNoYes *: 3 cannot be used as a table constraint. However, you can approximate the results by using This snippet defines a 8 table with one of the columns being an |