Yahoo Web Search

Search results

1. Top results related to define constraint in dbms

   • #define in #define; what happens in the preprocessor?

     Top Answer

     Answered Dec 08, 2013 · 6 votes

     The C standard has a special terminology for how macros are expanded.

     Macro names are, in effect, stored in a big table of "all macros defined at this time". Each table entry "macro name" on the left (and any arguments in the middle) and "expansion token-stream" on the right.

     When a macro is to be expanded (because it occurs in some non-preprocessor line, or in a position in a preprocessor line in which it must be expanded -- e.g., you can #define STDIO <stdio.h> and then #include STDIO), the table entry is "painted blue", and then the replacement token-stream is read (with argument expansion as also dictated by the standard).

     If the replacement token-stream contains the original macro name, it no longer matches, because the "blue paint" covers up the name.

     When the replacement token-stream has been fully handled, the "blue paint" is removed, re-exposing the name.

     Thus:

     #define X 5-

     adds X: (no arguments), 5 to the table.

     Then:

     #define Y X-

     adds: Y: (no arguments), X to the table.

     Somewhere later in the file, you might have an occurrence of the token Y. Assuming neither of the above have been #undefed (removed from the table), the compiler must first "paint the table entry for Y blue" and replace the token Y with the token X.

     Next, the compiler must "paint the table entry for X blue" and replace the token X with the token 5.

     The token 5 is not a preprocessor macro name (it can't be by definition) so the token 5 passes beyond the reach of the preprocessing phase. Now the "blue paint" is removed from the X table entry, as that's done; and then the "blue paint" is removed from the Y entry, which is also done.

     If you were to write instead:

     #define Y Y, Y, Y, the letter is called Y!-

     then the sequence, on encountering a later token Y, would be:

     • paint entry for Y blue
     • drop in replacement token sequence: Y , Y , Y , the letter is called Y !
     • check each replacement token in the table -- since Y is painted blue those don't match, and , cannot match, so those are all passed on to the rest of the compiler; the, letter, is, and called must be checked but are probably not in the table and hence passed on; Y is still painted blue so does not match and is passed on, and ! cannot match and is passed on.
     • remove blue paint, restoring the expansion

     Check all answers on Stack Overflow

     1/5

   • DBMS_LOCK usage in PL/SQL

     Top Answer

     Answered Nov 18, 2022 · 0 votes

     If you do not provide a timeout to wait when calling DBMS_LOCK.REQUEST

     , it will use MAXWAIT default value. This value is described in the same page and has the following semantics:

     maxwait constant integer := 32767;

     The constant maxwait waits forever.

     So as long as the lock is requested in X mode (Exclusive), all other sessions will not execute all the below code (including select and update) unless the lock will be released. They will not get any value of P_NUMBER in the output.

     When the lock is released in a correct way (not by timeout), processed rows will have PROCESS_S=1 and will not fulfill where predicate of select statement: where PROCESS_S=0 and ROWNUM=1;

     But if (for some reason) the lock will expire between select and update, it may provide the same P_NUMBER to different sessions of the application. It may be handled by select ... for update skip locked, that will not expire if the session is active.

     Check all answers on Stack Overflow

     2/5

   • DBMS_JOB.Broken in oracle

     Top Answer

     Answered Nov 22, 2022 · 0 votes

     I don’t think there is a specific api to mark a job as broken in dbms_scheduler but there is one to enable it again:

     DBMS_SCHEDULER.enable(name=>'test_job');-

     There is an api to change after how many failures a job will be disabled:

     DBMS_SCHEDULER.set_attribute (name=>'test_job', attribute=>'max_failures',value=>3);-

     Check all answers on Stack Overflow

     3/5

   • Constraint Violated in SQL

     Top Answer

     Answered Mar 24, 2014 · 2 votes

     This answer was in response to the original version of the question, it has since been edited which makes the answer seem irrelevant.

     The CHECK

     constraint for ORDERSTATUS

     demands that ORDERSTATUS

     is one of eitherIn Progress

     , Fulfilled

     , BackOrder

     or Cancelled

     , but in your insert query you use In Process

     which violates the constraint. I'm guessing you meant to use In Progress

     ?

     The error [Err] ORA-02291: integrity constraint (SCOTT.SOFKEY2) violated - parent key not found

     indicates that the SALESMANNO S00001 doesn't exist in the SALESMAN_MASTER2_56 table

     Check all answers on Stack Overflow

     4/5

   • DBMS.OUTPUT_PUT.LINE in C# using MSSql

     Top Answer

     Answered Mar 15, 2018 · 1 votes

     If you are trying to get additional text data from an operation to be returned from a SQL operation similar to how DBMS_OUTPUT.PUT_LINE works, then PRINT

     allows that. Since you mention C#, you should note that to consume PRINT data you need to subscribe to the SqlConnection.InfoMessage event, as described here.

     However, in most cases it is more suitable / pragmatic to SELECT (perhaps via OUTPUT

     -clause in the case of INSERT/DELETE operations) something that informs the UI - perhaps the rows, perhaps the @@ROWCOUNT, perhaps the SCOPE_IDENTITY(). PRINT is usually a bad option for anything other than tool scripts.

     Check all answers on Stack Overflow

     5/5

   Show moreShow less

2. www.prepbytes.com › blog › dbmsConstraints in DBMS: Types and Examples

   www.prepbytes.com › blog › dbms

   • Cached

   Nov 14, 2022 · The purpose of constraints is to enforce data quality and prevent data inconsistencies, thereby enhancing the overall data integrity and reliability of the database. Constraints define boundaries for data values, relationships between entities, uniqueness requirements, and more.

3. www.w3schools.com › sql › sql_constraintsSQL Constraints - W3Schools

   www.w3schools.com › sql › sql_constraints

   • Cached

   SQL constraints are used to specify rules for the data in a table. Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted. Constraints can be column level or table level.

   Syntax

   CREATE TABLEtable_name

   (

   column_name1 data_type(size)constraint_name,

   column_name2 data_type(size)constraint_name,

   column_name3 data_type(size)constraint_name,...

4. People also ask

   What are SQL constraints?

   • Frequently used SQL constraints include: NOT NULL – The column value cannot be empty (i.e. cannot contain a null value). UNIQUE – The column cannot contain duplicate values (i.e. all values in the column must be different). PRIMARY KEY – Each column value must uniquely identify that row in the table.

   What Is a SQL Constraint? | LearnSQL.com

   learnsql.com/blog/what-is-sql-constraint/

   See all results for this question

   What are DBMS constraints?

   • Constraints define rules and conditions that govern the data within a database, ensuring accuracy, consistency, and adherence to business rules. Understanding the various types of constraints in DBMS is essential for database administrators, developers, and data professionals to design robust databases and enforce data integrity.

   Constraints in DBMS: Types and Examples

   www.prepbytes.com/blog/dbms/constraints-in-dbms-and-types/

   See all results for this question

   What is a database constraint?

   • Constraints serve as a set of predefined rules that govern the behavior and relationships of the data in a database, helping to maintain its accuracy and reliability. The purpose of constraints is to enforce data quality and prevent data inconsistencies, thereby enhancing the overall data integrity and reliability of the database.

   Constraints in DBMS: Types and Examples

   www.prepbytes.com/blog/dbms/constraints-in-dbms-and-types/

   See all results for this question

   What is a NOT NULL constraint in SQL?

   • These rules control the data that can be stored in a column. For example, if a column has NOT NULL constraint, it means the column cannot store NULL values. The constraints used in SQL are: Note: These constraints are also called integrity constraints. The NOT NULL constraint in a column means that the column cannot store NULL values.

   SQL Constraints (With Examples) - Programiz

   www.programiz.com/sql/constraints

   See all results for this question

5. learnsql.com › blog › what-is-sql-constraintWhat Is a SQL Constraint? | LearnSQL.com

   learnsql.com › blog › what-is-sql-constraint

   • Cached

   Nov 19, 2020 · A SQL constraint is a rule for ensuring the correctness of data in a table. Frequently used SQL constraints include: NOT NULL – The column value cannot be empty (i.e. cannot contain a null value). UNIQUE – The column cannot contain duplicate values (i.e. all values in the column must be different).

6. www.geeksforgeeks.org › sql-constraintsSQL | Constraints - GeeksforGeeks

   www.geeksforgeeks.org › sql-constraints

   • Cached

   • Video Duration: 17 min

   • NOT NULL. If we specify a field in a table to be NOT NULL. Then the field will never accept null value. That is, you will be not allowed to insert a new row in the table without specifying any value to this field.
   • UNIQUE. This constraint helps to uniquely identify each row in the table. i.e. for a particular column, all the rows should have unique values. We can have more than one UNIQUE columns in a table.
   • PRIMARY KEY. Primary Key is a field which uniquely identifies each row in the table. If a field in a table as primary key, then the field will not be able to contain NULL values as well as all the rows should have unique values for this field.
   • FOREIGN KEY. Foreign Key is a field in a table which uniquely identifies each row of a another table. That is, this field points to primary key of another table.

7. www.vertabelo.com › blog › database-constraintsDatabase Constraints: What They Are and How to Define Them in ...

   www.vertabelo.com › blog › database-constraints

   • Cached

   • Primary Key Constraint. Definition and Example. The PRIMARY KEY constraint is defined on one or more columns in a table. It indicates that this column (or set of columns) must uniquely identify each row of the table.
   • Foreign Key Constraint. Definition and Example. The FOREIGN KEY constraint is defined on one or more columns in a table as a reference to the PRIMARY KEY column(s) of another table.
   • Not Null Constraint. Definition and Example. The NOT NULL constraint – as its name indicates – prevents the column that implements it from storing null values.
   • Unique Constraint. Definition and Example. The UNIQUE constraint prohibits the column that implements it from storing duplicate values. One UNIQUE constraint can also contain multiple columns; in such a case, the combination of these columns must be unique.

8. www.databasestar.com › sql-constraintsSQL Constraints: The Complete Guide - Database Star

   www.databasestar.com › sql-constraints

   • Cached

   Oct 11, 2022 · A constraint is a rule that you define on a table that restricts the values in that table. They can be added to a table or a view when you create it, or after it’s created. You do this by specifying a few keywords and some information about the columns and rules you want to set.

9. www.programiz.com › sql › constraintsSQL Constraints (With Examples) - Programiz

   www.programiz.com › sql › constraints

   • Cached

   In a database table, we can add rules to a column known as constraints. These rules control the data that can be stored in a column. For example, if a column has NOT NULL constraint, it means the column cannot store NULL values. The constraints used in SQL are: Note: These constraints are also called integrity constraints. NOT NULL Constraint.