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.

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).

2009年12月4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.

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

2009年1月14日 · Update myTable set MyColumn = NULL This would set the entire column to null as the Question Title asks. To set a specific row on a specific column to null use: Update myTable set MyColumn = NULL where Field = Condition. This would set a …

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.

2011年12月28日 · Check the not null condition and empty string in SQL command is use 'is null / not null' and '!='. please try this sample pattern script: SELECT * FROM [Employee] WHERE EMail is not null -- not null check and Email != '' -- not empty check

The TRIM function in SQL is used to remove specified prefix or suffix from a string. The most common pattern being removed is white spaces. This function is called differently in different databases: MySQL: TRIM(), RTRIM(), LTRIM() Oracle: RTRIM(), LTRIM() SQL Server: TRIM(), RTRIM(), LTRIM() How to Check Empty/Null/Whitespace :-

2013年3月15日 · 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

2013年1月4日 · However, I need it to just return a NULL for that column if there is no match and still return the value from Table1. I have changed up the JOIN with everything that I can think of, but to no avail. Table2.Category can contain multiple other values, so doing a OR IS NULL type of deal won't work.