comparing null values in sql

thing we should think about is to just give the sort numbers that need to be in front, and the other is null;Mysql> select * from Bjy_order;+----+------+--------------+|ID |City | Order_number |+----+------+--------------+|1 |Beijing | NULL ||2 |Shanghai | 1 ||3 |guangzhou | NULL ||4 |Hebei | NULL ||5 |Tianjin | 2 ||6

constraint that applies only to this column, isunique must be true. False: In the base table, this column can contain duplicate values. The default value of this column is false.Iskey true: This column is a column that uniquely identifies a group of columns in a row set. A group of columns whose iskey is set to true must uniquely identify a row in the row set. This column is not required to be the smallest column set. This set of columns can be gener

Show create TABLE table name-Displays the SQL statement that created the table.Adds a new column to an existing table.ALTER TABLE name add column name int null--this line adds an int type to the default nullable column.Null means: An undefined value.How do I compare the value of a column to null?Can be null,is not

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

Environment: At the beginning, Oracle10g came into contact with the pascal language, so sometimes it is not very fond of the C language syntax. There is a lazy way of writing in C Language (also exists in java) Environment: Oracle 10g was initially exposed to the pascal language, so sometimes it is not very fond of the C language syntax. There is a lazy way of writing in C Language (also exists in java) Environment: Oracle 10g In the first place, we came into contact with the pascal Languag

above null value index, non-null value is not indexed, so that the index will be very small, efficient query. But when writing SQL, you need to be aware that the predicate condition must be consistent with the function. Create INDEX ind_01 on t01 (decode (col01,null,1,null)

Oracle uses orderby to sort null values. When order by is used in Oracle for query and sorting, if there is a null value in the sorting field, the sorting result may not reach the expected result. For example: [SQL] view plain copy Select * from test order by age desc; Sort by age field in descending order. The re

an error! What's the reason? The Version_list field is currently NULL and the INSERT statement above attempts to do this: table (NULL), which is to convert the null object into a table. It's counterintuitive, Oracle can't do it! So how to solve it? The Version_list field is NULL because we did not initialize it at

Processing of inserting int null values in mysql bitsCN.com The best and most commonly used method is: If the int type null value is not allowed to be null, the default value is 0. this will not result in the case that the null value can be inserted 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 "

First I say what is Oracle's function, once a Daniel, let me talk about the familiar Oracle function, I was confused, thought "What Oracle function Ah, is not those SQL statements," then I actually uttered a select answer, he almost angry, Repeatedly stressed: "I said is the Oracle function", later he said, function can be understood as with parentheses (), then I slowly sensible after, often Baidu Oracle function, every time there is an interview or

Oracle uses orderby to sort null values When order by is used in Oracle for query and sorting, if there is a null value in the sorting field, the sorting result may not reach the expected result. For example: Select * from test order by age desc; Sort by age field in descending order. The result is as follows: Change the

How to import additional fields in Oracle as null values Q: We have migrated our Oracle database to a new environment. Some customer tables exist in two databases at the same time, but those tables in the new environment have some additional fields. Can you help me use the import/export tool? In this way, I can either import a new null value or export it as a

How does php determine whether multiple post values are empty? this post is finally edited by gz109 from 2013-07-, for example, a form, multiple options, how can I use php to determine whether the value is null or the correct value? lt; form nbsp; action = "add. php " nbsp; method =" p php how can I determine whether multiple post values are empty? This post wa

How does php determine whether multiple post values are empty? this post is finally edited by gz109 from 2013-07-, for example, a form, multiple options, how can I use php to determine whether the value is null or the correct value? lt; form nbsp; actionadd. php nbsp; methodpost gt; lt; input nbsp; how does typ php determine whether multiple post values are

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

Is not null and! in Oracle SQL! = NULL: is not null and! = NULL. We often encounter database conditions! = NULL, but the returned result is a NULL set. In fact, the difference is not fu

Prompt for running the project today"Constraints cannot be enabled. One or more rows contain values that violate non-null, unique, or foreign key constraints ." . I found some reason online: http://www.cnblogs.com/muzihai1988/archive/2011/05/04/2036502.html Cause analysis:The query results of a strongly typed able and SQL statement do not match. In shor

The best way to deal with the insertion of int null values in mysql is to: www.2cto.com. in this way, the null value is not allowed to be inserted as 0. Although it is necessary to judge when it is used up, there will be no problems. Other methods are from the network. If you have not verified the installation, go to my. search for

MyBatis you want to insert a null value, you need to specify JdbctypeMyBatis Insert NULL returns an empty value exception, but PL/SQL does not prompt for errors, mainly because MyBatis cannot be converted There is also the MYBATIS3 error setting null parameter when inserting data to Oracle. Most of the JDBC drivers