Select null date in db2

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This is the case regardless of whether the column is set to null or not. DB2 for Linux, Unix, and Windows has a compression option that allows columns set to null to save space. Using this option causes DB2 to eliminate the unused space from a row where columns are set to null. This option is not available on the mainframe, though. Every column defined to a DB2 table must be designated as either allowing or disallowing nulls. Null is the default if nothing is specified after the column name.

Remember, null is a lack of a value, so the column does not equal anything. When inserting data, if the user fails to make an entry in a column that allows nulls, DB2 supplies the NULL as a default unless another default value exists.

Whenever possible, avoid nulls in columns that must participate in arithmetic logic for example, DECIMAL money values , and especially when functions will be used. To clarify with an example, if the COMM column is nullable, the result of the following query:. DB2 checks to ensure that only valid dates, times, and timestamps are placed in columns defined as such.

If the column can be unknown, it must be defined to be nullable because the default for these columns is the current date, current time, and current timestamp unless explicitly defined otherwise using the DEFAULT clause.

Null, therefore, is the only viable option for the recording of missing dates, times, and timestamps unless you pick a specific valid date that is not used by your applications to indicate unknown. For every other column, determine whether nullability can be of benefit before allowing nulls. Examine these rules closely. This inconsistent handling of nulls is an anomaly that you must remember when using nulls. The following are several sample SQL queries and the effect nulls have on them.

This query returns the average salary for each type of job. All instances in which JOB is null will group at the bottom of the output. This query retrieves all occurrences in which the project start date is equal to the project end date. This information is clearly erroneous, as anyone who has ever worked on a software development project can attest.

The query does not return any rows in which either dates or both dates are null for two reasons: 1 two null columns are never equal for purposes of comparison, and 2 when either column of a comparison operator is null, the result is unknown. When creating tables, treat nullable columns the same as you would any other column. Some DBAs advise you to place nullable columns of the same data type after non-nullable columns.

This is supposed to assist in administering the null columns, but it does not really help — and it might hurt. Sequencing nullable columns in this manner provides no clear benefit and should be avoided. Nulls are clearly one of the most misunderstood features of DB2 — indeed, of most SQL database systems. Although nulls can be confusing, you cannot bury your head in the sand and ignore nulls if you choose to use DB2 as your DBMS.

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Popular Course in this category. Collectives on Stack Overflow. Learn more. Asked 8 years, 5 months ago. Active 3 months ago. Viewed 18k times. Am I doing something wrong? Improve this question. Arcadian Arcadian 4, 12 12 gold badges 61 61 silver badges bronze badges. What version of DB2 are you using?

As long as the date field is nullable, you can set a date field to null. The field might be defined as "Not Null" — Bruce Martin. Add a comment. Active Oldest Votes. You can of course set a date column to a NULL value. How do you do that?