sql - Not equal <> != operator on NULL - Stack Overflow
2014年10月9日 · In SQL, anything you evaluate / compute with NULL results into UNKNOWN This is why SELECT * FROM MyTable WHERE MyColumn != NULL or SELECT * FROM MyTable WHERE MyColumn <> NULL gives you 0 results. To provide a check for NULL values, isNull function is provided.
Why does NULL = NULL evaluate to false in SQL server
2009年12月3日 · The SQL language suffers the problem of backwards compatibility. NULL found its way into SQL and we are stuck with it. Arguably, the implementation of NULL in SQL is flawed (SQL Server's implementation makes things even more complicated due to its ANSI_NULLS option). I recommend avoiding the use of NULLable columns in base tables.
SQL is null and = null - Stack Overflow
2012年3月6日 · In SQL, a comparison between a null value and any other value (including another null) using a comparison operator (eg =, !=, <, etc) will result in a null, which is considered as false for the purposes of a where clause (strictly speaking, it's "not true", rather than "false", but the effect is the same).
sql - IN Clause with NULL or IS NULL - Stack Overflow
Null is formally defined as a value that is unavailable, unassigned, unknown or inapplicable (OCA Oracle Database 12c, SQL Fundamentals I Exam Guide, p87). So, you may not see records with columns containing null values when said columns are restricted using an "in" or "not in" clauses.
sql - Select rows where column is null - Stack Overflow
2011年5月18日 · SELECT * FROM customers WHERE first_name IS NULL On MS SQL Server, the ISNULL() function returns the first argument if it's not NULL, otherwise it returns the second. You can effectively use this to make sure a query always yields a value instead of NULL, e.g.: SELECT ISNULL(column1, 'No value found') FROM mytable WHERE column2 = 23
What's the difference between " = null" and " IS NULL"?
The SQL-92 standard requires that an equals (=) or not equal to (<>) comparison against a null value evaluates to FALSE. When SET ANSI_NULLS is ON, a SELECT statement using WHERE column_name = NULL returns zero rows even if there are null values in column_name.
SQL: What does NULL as ColumnName imply - Stack Overflow
In the statement result we have a column that has all NULL values. We can refer to that column using alias. In your case the query selects all records from table, and each result record has additional column containing only NULL values.
T-SQL CASE Clause: How to specify WHEN NULL - Stack Overflow
Consider the following statements (which is BTW illegal in SQL Server T-SQL but is valid in My-SQL, however this is what ANSI defines for null, and can be verified even in SQL Server by using case statements etc.) SELECT NULL = NULL -- Results in NULL. SELECT NULL <> NULL -- Results in NULL
NULL usage in WHERE IN SQL statement - Stack Overflow
2012年4月19日 · To compare null values you should use is null operator. Null has an specific treatment. Sample: select case when null in (null) then 1 else 0 end returns 0 Remember Codd rule 3: Rule 3: Systematic treatment of null values: The DBMS must allow each field to remain null (or empty). Specifically, it must support a representation of "missing ...
SQL Query - how do filter by null or not null - Stack Overflow
2016年1月5日 · Example(NULL) select * from user_registration where registered_time IS NULL will return the rows with registered_time value is NULL. Example(NOT NULL) select * from user_registration where registered_time IS NOT NULL will return the rows with registered_time value is NOT NULL Note: The keyword null, not null and is are not case sensitive.