How check DataReader is NULL?

How check DataReader is NULL?

stirng query = “SELECT ColumnA FROM MyTable WHERE ColumnB = ‘some condition'”; //… initialize connection and command and reader classes //then do: if(reader. Read()) //if there are any value(s) { if(reader. GetValue(0) != DbNull.

How do you retrieve NULL values from a database?

How to Test for NULL Values?

  1. SELECT column_names. FROM table_name. WHERE column_name IS NULL;
  2. SELECT column_names. FROM table_name. WHERE column_name IS NOT NULL;
  3. Example. SELECT CustomerName, ContactName, Address. FROM Customers. WHERE Address IS NULL;
  4. Example. SELECT CustomerName, ContactName, Address. FROM Customers.

How do you deal with NULL values in DBMS?

How to Count SQL NULL values in a column?

  1. SELECT SUM(CASE WHEN Title is null THEN 1 ELSE 0 END)
  2. AS [Number Of Null Values]
  3. , COUNT(Title) AS [Number Of Non-Null Values]

Should NULL values be allowed in a database?

Using NULL values in your database is a permanent choice. Once you choose to allow them, you need to allow NULLs in all SQL database tables. Relational databases include NULLs by default, but they all let you reject NULLs should you decide to require developers to enter a value.

How do I know if my Datareader has rows?

Remarks. The HasRows property returns information about the current result set. If the DataTableReader contains multiple result sets, you can examine the value of the HasRows property immediately after you call the NextResult method in order to determine whether the new result set contains rows.

How do I check if a Datareader has a column?

string ColumnValue; if (dr[“ColumnName”] != null) ColumnValue = dr[“ColumnName”]. ToString(); if (dr.

IS null null in SQL?

The expression “NULL = NULL” evaluates to NULL, but is actually invalid in SQL; yet ORDER BY treats NULLs as equal (whatever they precede or follow “regular” values is left to DBMS vendor). The expression “x IS NOT NULL” is not equal to “NOT(x IS NULL)”, as is the case in 2VL.

How do I count null as zero in SQL?

The only way to get zero counts is to use an OUTER join against a list of the distinct values you want to see zero counts for. SQL generally has a problem returning the values that aren’t in a table.

What is NULL value in DBMS?

A null value in a relational database is used when the value in a column is unknown or missing. A null is neither an empty string (for character or datetime data types) nor a zero value (for numeric data types). SqlTypes has its own IsNull property and a Null value that can be assigned to an instance of that data type.


IS NULL replace SQL Server?

We can replace NULL values with a specific value using the SQL Server ISNULL Function. The syntax for the SQL ISNULL function is as follow. The SQL Server ISNULL function returns the replacement value if the first parameter expression evaluates to NULL.

What is a NULL value in a database?

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