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How do you handle NULL values in joins?
Since it’s not possible to join on NULL values in SQL Server like you might expect, we need to be creative to achieve the results we want. One option is to make our AccountType column NOT NULL and set some other default value. Another option is to create a new column that will act as a surrogate key to join on instead.
What function would you use to remove NULL values when using a left join?
You can use ISNULL(MAX(T2. LOGIN_TIME), ‘Default Value’) to replace the NULL . But first you should consider that LOGIN_TIME varchar(255) with values such as 17.07. 17 that holds dates should be DATE data type.
Do joins work on NULL values?
As we have seen from the above examples joining NULL values does not work. Even though you have two NULL values SQL Server does not treat these as the same value. Internally a value of NULL is an unknown value and therefore SQL Server does not equate an unknown value being equal to another unknown value.
How will you include null values in a row?
There are three ways to assign a NULL value to a column on insertion:
- Ignore the column.
- Assign a NULL value to the column. This is standard SQL practice.
- Use indicator variables.
When to use a left join?
Use a left join when you want all the results from Table A, but if Table B has data relevant to some of Table A’s records, then you also want to use that data in the same query. Use a full join when you want all the results from both Tables.
How does left_join really work?
The LEFT JOIN clause allows you to query data from multiple tables. It returns all rows from the left table and the matching rows from the right table. If no matching rows found in the right table, NULL are used. The following illustrates how to join two tables T1 and T2 using the LEFT JOIN clause:
Do left outer joins and left join the same?
In SQL server, the keyword outer is optional when you apply left outer join. Thus, it does not make any difference if you either write ‘LEFT OUTER JOIN’ or ‘LEFT JOIN’ as both are going to give you the same result. A LEFT JOIN B is an equivalent syntax to A LEFT OUTER JOIN B. Below is the list of equivalent syntaxes in the SQL server:
What is left join /right join?
A left join refers to keeping all of the records from the 1st table irrespective of result, and the insertion of NULL values when the second table values do not match. A right join, on the other hand, refers to keeping all of the records coming from the 2nd table irrespective of what the result is,…