1 Introduction to null valuesNULL is a unique data type in the database. If a column in a record is NULL, the value of this column is unknown and uncertain. Since it is unknown, there are several possibilities. Therefore, NULL is not a definite
In the database, a null value is used to indicate that the actual value is unknown or meaningless. In a table, if a column in a row has no value, it is called NULL ). A null value can be returned for any data type column as long as the non-NULL or
Oracle in the database, null values are used to indicate a situation where the actual value is unknown or meaningless. In a table, if a column in a row has no value, it is called a null value (NULL). Columns of any data type can have null values if
---DQL: Data query statementsThe---Select statement must contain at least two words, namely the Select and from words.---the SELECT clause to specify the field to query.---the table that the FROM clause uses to customize the data source. The--select
The introduction of 1null value NULL is a unique data type in the database. When a column in a record is NULL, the value of this column is unknown and uncertain. Since it is unknown, there are several possibilities. Therefore, NULL is not a definite
When the string is empty, it is judged by where null is used.
Example:
CREATE TABLE Test(Stuno Number (Ten) primary key,Stuname VARCHAR2 (50))INSERT into Test (Stuno) VALUES (10)INSERT into Test (stuno,stuname) VALUES (11, ')
SELECT * FROM test
Some people have summarized the concept of Null value in the database, which is more refined. The excerpt is as follows:
Null is a unique data type in the database. If a column in a record is Null, the value of this column is unknown and uncertain.
The difference between Null and NULL String ''in Oracle: Q: What is Null? A: When we do not know the specific data, it is also unknown. We can use NULL. We call it NULL. in ORACLE, the column length containing NULL values is zero. ORACLE allows
Comparison of concurrency control (LOCK) between DB2 and Oracle
Comparison of concurrency control (LOCK) between DB2 and Oracle
1 Introduction
The minimal recovery and transaction units in relational databases (DB2, Oracle, Sybase, Informix, and
Oracle string comparison --- null in ORACLE, the NULL String is treated as NULL, and the comparison result of any value and NULL is null. In this way, an exception occurs when comparing two strings. See the following example: DECLARE I VARCHAR2 (10):
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