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* MySQL SQL syntax: {{kbd | key = SELECT * FROM table WHERE column IS NULL;}}<ref>[http://dev.mysql.com/doc/refman/5.0/en/working-with-null.html MySQL :: MySQL 5.0 Reference Manual :: 3.3.4.6 Working with NULL Values]</ref> | * MySQL SQL syntax: {{kbd | key = SELECT * FROM table WHERE column IS NULL;}}<ref>[http://dev.mysql.com/doc/refman/5.0/en/working-with-null.html MySQL :: MySQL 5.0 Reference Manual :: 3.3.4.6 Working with NULL Values]</ref> | ||
* R: is.null(): [https://stat.ethz.ch/R-manual/R-devel/library/base/html/NULL.html R: The Null Object] | * R: is.null(): [https://stat.ethz.ch/R-manual/R-devel/library/base/html/NULL.html R: The Null Object] | ||
* Excel<ref>[https://errerrors.blogspot.com/2018/09/check-if-cell-value-is-null-in-excel.html 如何判斷 Excel 儲存格的欄位值是 NULL]</ref> | |||
Find whether a variable is NOT NULL | Find whether a variable is NOT NULL | ||