oracle sql not null

Tags: image false strong another rule for anti-avoidance technologyFirst, SQL SERVER is a three-valued logic that predicate evaluates to True,false,unknown The standard predicates are those that follow this rule. If slary>0 returns a result that evaluates to true the row rejects false and the unknown result But not all predicate processing is like this if it appears in a check constraint that evaluates to False to deny false means to accept true and u

Original: null value problem in SQL ServerSQL uses three-valued predicate logic, so the result returned by a logical expression can be true, false, or unknown, and returning true in the three-value logic is not exactly the same as not returning false.SQL handling of query filtering conditions: Accept Ture deny false and unknownSQL handling of CHECK constraints: Accept FALSE deny TRUE and UNKnown

SQL NOT NULL constraint syntax and NOT NULL instance If we create a table CREATE TABLE AA(id_p int not NULL,LName varchar () not NULL,FName varchar (25),Ass varchar (25),C varchar (205)) The NOT NULL constraint enforces that th

The table structure is created like the following code Copy Code code as follows: CREATE TABLE TEST_TB ( TestID int NOT null identity (1,1) primary key, Caption nvarchar (MB) null ); Go Solution 1: The first idea for this question may be: Is it OK to add a unique key to the caption field? OK, let's follow this thread and create a unique index first. Copy Code code as

I. Differences between NULL in SQL Server and DBNULL in. NET and NULL in programming languages1: NULL in SQL ServerThe NULL value in SQL Server IS expressed as "

Tags: that is greater than stronggrouplov in insert get address When we want to query all result sets in SQL for which a column value is NULL, the query condition should write like thisSELECT * FROM table where field is nullInstead, use the SELECT * from table where field = NULL to not find the correct result. Then why is this? To understand why, you need to

NullNoGreater than/less than/equal to/not equal to any value (including null itself), and only:Null is null SQL> set serveroutput on

Solution 1: for this problem, the first thought may be: Can I add a unique key to the caption field? Well, let's proceed with this idea and create a unique index first. Nbsp; Code: createuniquenonclusteredindexun_test_tbontest_tb (caption) go index has been created. Let's test the effect nbsp; Code: I solution 1: For this question, the first thought may be: Can I add a unique key to the caption field? Well, let's proceed with this idea and create a unique index first. The Code is as follows: C

Solution 1:The first idea for this question may be: Is it OK to add a unique key to the caption field? OK, let's follow this thread and create a unique index first.The code is as follows:Create unique nonclustered index UN_TEST_TBOn TEST_TB (caption)Go Index creation Okay, let's test the effect.The code is as follows:Insert into TEST_TB (caption)VALUES (NULL)GoInsert into TEST_TB (caption)VALUES (NULL)Go

Error behavior: Microsoft OLE DB Provider for SQL Server error ' 80040e2f ' cannot insert value NULL into column ' id ', table ' Web.dbo.dingdan '; column does not allow null values. INSERT failed. /untitled-2.asp, line 115 Reason Analysis: SQL database, the ID column identification specification is not set to Ye

Sometimes the following error occurs when you create a SQL Server job with an SQL statement: MSG 515, Level 16, State 2, procedure sp_add_job, line 137th Cannot insert value NULL into column ' owner_sid ', table ' msdb.dbo.sysjobs '; column does not allow null values. INSERT failed. Statement has been

Tags: tab har ble col char ref SQL Server target sizeTransferred from: http://www.maomao365.com/?p=6965Summary:Here are two ways to share a null value in a field with a specified value, as follows:Lab environment: SQL Server R2 Cases:Create TableTest (keyIdint Identity, infovarchar( -))GoInsert intoTest (Info)Values('a'),('b'),(

determine whether it is the length of zero is the field is empty! So the code changes to this: Select * from where = NULL and datalength (Resultremarks) = 0 And there was nothing, and this time we looked at the data. It is found that the null value ZAI the database has a special meaning, which is different from the field containing 0, an empty string, or simply containing a space. So to determine whethe

Procedure Querylacklonorlattdcell (I_region_name varchar2, i_state varchar2) isbegin Select Region_name, state From gc3_td_site_history where 1 = 1 and region_name = decode (i_region_name, NULL, Region_name, i_ Region_name) and InStr (decode (i_state, NULL, State, i_state), state) > 0;end;If I_region_name is null, all region_name are queried

bigint No Calendarquartername nvarchar (30) No CalendarYear bigint No CalendarYearName nvarchar (30) No Fiscalmonthname nvarchar (30) No Fiscalmonthofyear bigint No Fiscalquarter bigint No Fiscalquartername nvarchar (30) No

SQL uses three-valued predicate logic, so the result returned by a logical expression can be true, false, or unknown, and returning true in the three-value logic is not exactly the same as not returning false.SQL handling of query filtering conditions: Accept Ture deny false and unknownSQL handling of CHECK constraints: Accept FALSE deny TRUE and UNKnown the subtlety of unknown is when it is reversed results are still unknown ,

UNIQUE constraint in the "id_p" column when the "Persons" table is created:Mysql:CREATE TABLE Persons (id_p int not null,lastname varchar (255) not null,firstname varchar (255), Address varchar (255), City VA Rchar (255), UNIQUE (Id_P) )SQL Server/oracle/ms Access:UNIQUE, LastName varchar (255) not

Tags: os SP data BS Database SQL nbsp Table method1.DataTable DT; Assuming the field is name, DT has saved the datadt.rows[0]["name"] = = System.DBNull.Value; Determines whether the name field of the first row of data is empty2.DataTable DT; Assuming the field is name, DT has saved the datadt.rows[0]["Name"]. ToString () = = ""; Determines whether the name field of the first row of data is empty3.DataTable DT; Assuming the field is name, DT has saved

(1, 'jia ', NULL, 1000, NULL ); SQL> select * from emp where empno = 1; EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO ------------------------------------------------------------------------- 1, JIA 1000 We can see that the new row is inserted. Except for the null values of job and comm, The mgr, hiredate, and deptno

as null values. SQL >insert into EMP (EMPNO,ENAME,JOB,SAL,COMM) VALUES (1, ' JIA ', null,1000,null); SQL >select * from EMP where empno=1; EMPNO ename JOB MGR hiredate SAL COMM DEPTNO-------------------------------------------------------1 JIA 1000 ----You can see the newl